Informacija

Kako bi infekcija komaraca sterilizirajućom bakterijom imala ikakvog učinka?

Kako bi infekcija komaraca sterilizirajućom bakterijom imala ikakvog učinka?



We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

Prema ovom članku iz New York Posta, SAD je upravo odobrio masovno puštanje mužjaka komaraca zaraženih bakterijom koja ih sterilizira. Ideja je, prema članku i nekim zaključcima, da se pare s ženkama komaraca i impregniraju ih neodrživim jajima, uzrokujući nestanak generacije komaraca. Sjajno, zar ne?

Pa ne. Muški komarci, prema onome što mogu sakupiti, obično žive manje od tjedan dana u svojoj odrasloj fazi, pare se možda jednom, dok će ženke živjeti nekoliko tjedana pareći se, hraneći se, polažući jaja i ponavljajući se dok ne umru. Čak i ako se i mužjaci i ženke uspiju pariti samo jednom, za svaku ženku koju ne želite proizvesti održivo mladunče, trebate osloboditi jednog zaraženog mužjaka. Uz vrlo konzervativnu procjenu od 10 bilijuna komaraca u Sjedinjenim Državama, jednu generaciju godišnje i trenutno odvajanje mužjaka od ženki komaraca u laboratoriju ručno prema članku, morali biste ručno zaraziti 10 bilijuna mužjaka komaraca godišnje, barem nekoliko godina, kako biste napravili ozbiljnu ozljedu u populaciji komaraca.

Kako netko misli da je ovo praktična ideja?


Isključivač mikrobiote za razumijevanje interakcija komaraca i bakterija

Bakterije koje zahtijevaju posebnu prehranu mogu prolazno kolonizirati ličinke komaraca i omogućiti proizvodnju komaraca bez klica, proširujući mogućnosti proučavanja uloge mikroorganizama u razvoju komaraca i prijenosu patogena.

Suradnici

Autor

Mathilde Gendrin

Mlađi voditelj grupe, Institut Pasteur de la Guyane

Autor doprinosa

Ottavia Romoli

Post-doc, Institut Pasteur de la Guyane

Udio

Kopirajte vezu

Komarci se često opisuju kao najsmrtonosnije životinje na zemlji jer prenose brojne zarazne bolesti. Aedes aegypti osobito je glavni prijenosnik nekoliko virusa koji predstavljaju važno opterećenje za ljudsko zdravlje, uključujući viruse denga i Zika. Kad komarac ugrize nekoga da proguta njegovu krv, on također može steći takve viruse ako je osoba zaražena. Velika većina ovih virusnih čestica ubija se u crijevima komaraca, osobito zbog imunološkog sustava. Mali dio, međutim, izbjegava ovu barijeru, razmnožava se u tijelu komaraca i na kraju se može prenijeti na zdrave ljude tijekom sljedećih krvnih obroka.

U posljednjih petnaest godina postalo je jasno da mikrobi koji naseljavaju komarce igraju temeljnu ulogu u definiranju sudbine patogena u crijevima komaraca. Ova zajednica mikroorganizama ili mikrobiota mogla bi olakšati ili blokirati razvoj patogena u tijelu komaraca (i stoga njegovu vjerojatnost prenošenja). Na primjer, bakterija Enterobacter Esp_Z pokazao je svojstva protiv malarije inhibicijom antioksidativnog odgovora parazita malarije (1), dok Serratia marcescens proizvodi enzim koji probavlja sloj sluzi u crijevima komaraca, čineći ga propusnijim za infekciju virusom denga (2). No, mikrobiota općenito utječe na nekoliko aspekata biologije komaraca, imajući dodatni učinak na njezinu reprodukciju, ponašanje, preživljavanje, a time i na opći uspjeh populacije komaraca.

Životinjski modeli bez klica, lišeni bilo kakve mikrobiote, postali su temelj za proučavanje interakcija domaćin-mikrobiota. Uspostavljanje komaraca bez klica posebno je izazovno jer je za njihov normalan razvoj potrebna živa mikrobiota (3). Ako su jaja komarca mikrobiološki sterilizirana, izležene ličinke neće moći rasti u odsutnosti bakterija ako im se osigura sterilna uobičajena prehrana (slika 1a). Za proučavanje mikrobiote komaraca, pojedinci lišeni mikrobiote mogli su se dobiti samo lijekovima antibioticima, koji nisu potpuno učinkoviti, ili specifičnom sterilnom prehranom koja proizvodi zaostale jedinke (4).

Slika 1. Kad se jajašca komaraca mikrobiološki steriliziraju, izležene larve bez klica blokiraju se u njihovom razvoju (a). Koristili smo genetski modificirane bakterije koje zahtijevaju neke bitne hranjive tvari za rast (b). Kad se te bakterije i njihovi hranjivi sastojci isporuče ličinkama, razvoj komaraca je spašen. Čim se te hranjive tvari uklone iz okoline za uzgoj, zaustavlja se rast bakterija i dobivaju se komarci bez klica. Kolonizacija bakterija može se zaustaviti u različitim fazama razvoja komaraca, omogućujući proizvodnju ličinki ili odraslih osoba (c).

U našem dokumentu Nature Communications koji vodi dr. Ottavia Romoli, opisujemo metodu koja se temelji na prolaznoj kolonizaciji bakterija kako bi se dobilo bez klica Ae. aegypti bez ikakvog razvojnog deficita. Ova je metoda prethodno postavljena na miševima (5), a temelji se na upotrebi genetski modificiranih bakterija (Escherichia coli) za rast su potrebne dvije hranjive tvari specifične za bakterije. Kada se te bakterije opskrbe ličinkama komaraca zajedno s tim bitnim molekulama, razvoj larvi je spašen (slika 1b). Kada se bitne hranjive tvari uklone iz okoliša za uzgoj ličinki, rast bakterija je blokiran i komarci se oslobađaju od klica. Pomoću ove metode isključivanje mikrobiote komaraca moguće je u bilo koje vrijeme tijekom stadija larve i odrasle osobe (slika 1c).

Kad smo pritisnuli prekidač na kraju razvoja, otkrili smo da ova genetski modificirana bakterija podržava razvoj komaraca, kao i kontrolu nad divljim tipom, te proizvodi odrasle osobe bez ikakvih posebnih oštećenja plodnosti ili životnog vijeka. Također smo isključili mikrobiotu usred razvoja ličinki kako bismo istražili zašto je tako važno za larve. Utvrdili smo da bakterije doprinose razvoju komaraca davanjem vitamina, osobito folne kiseline, te povećanjem skladištenja energije lipida i proteina.

Vjerujemo da će ova metoda omogućiti daljnje istraživanje fascinantne uloge mikrobiote na komarce, te interakcije između mikrobiote i različitih patogena koje komarac može prenijeti.

(1) Cirimotich, C.M. et al. Prirodna vatrostalnost posredovana mikrobima Plazmodij infekcija u Anopheles gambiae. Znanost 332(6031):855-8 (2011).

(2) Wu, P. et al. Komenzalna bakterija u crijevima potiče propusnost komaraca za arboviruse. Stanični domaćin i pojačivač mikroba 25, 101-112 (2019).

(3) Coon K.L. et al. Komarci su domaćini zajednica bakterija koje su bitne za razvoj, ali se uvelike razlikuju među lokalnim staništima. Molekularna ekologija 25, 5806-5826 (2016).

(4) Correa, M.A. et al. Generacija aseničara Aedes aegypti pokazati da žive bakterije nisu potrebne za razvoj komaraca. Nature Communications 9, 4464 (2018).

(5) Hapfelmeier, S. et al. Reverzibilna mikrobna kolonizacija miševa bez klica otkriva dinamiku imunoloških odgovora IgA. Znanost 328, 1705–1709 (2010).


Pozadina

'Mikrobiom' je skup mikroorganizama unutar ili na tijelu. Kod komaraca mikrobiom, koji se sastoji od bakterija, virusa, protozoa i gljiva, duboko mijenja fenotipe domaćina. Na stjecanje i sastav mikrobioma utječe nekoliko abiotičkih i biotičkih čimbenika, uključujući genetiku domaćina i mikrobe [1,2,3,4] i okoliš [5,6,7]. Stoga se mikrobiomi komaraca mogu značajno razlikovati među pojedincima, životnim fazama, vrstama i na geografskom prostoru [8, 9], a ta varijacija vjerojatno doprinosi razlikama u fenotipovima domaćina [10]. Slično, vodoravni i okomiti put prijenosa koji mikrobi iskorištavaju da koloniziraju svog domaćina znače da komarci uzgojeni u laboratorijskim uvjetima imaju znatno drugačiji mikrobiom u odnosu na svoje kolege na terenu [11,12,13]. Stoga je provođenje studija s mikrobiomom relevantnim za područje bilo izazovno. Unutar komaraca mikrobi mogu invadirati i kolonizirati različita tkiva, možda unutarstaničnim putem [14], a čini se da reproduktivni organi [15, 16] i žlijezde slinovnice [17] imaju najveću raznolikost mikroba. Mikrobiota u srednjim crijevima ili žlijezdama slinovnicama ima potencijal izravne interakcije s patogenima, dok mikrobi koji borave u drugim tkivima mogu neizravno utjecati na kompetentnost vektora. Mikrobi koji se nalaze u crijevima ili drugim tkivima [18, 19] također mogu imati značaj za druge osobine povijesti života koje utječu na vektorsku sposobnost.

Vektorski kapacitet opisuje sposobnost populacije vektora za prijenos patogena na domaćina i predstavljen je jednadžbom vektorskog kapaciteta (slika 1). To je izradio Garret-Jones 1964. godine i predstavlja broj sekundarnih slučajeva vektorske infekcije po jedinici vremena s obzirom na uvođenje zarazne jedinke u naivnu populaciju [20, 21]. Prijenos patogena modeliran je jednadžbom vektorskog kapaciteta, koja je vektorski orijentirana prilagodba osnovnog reproduktivnog broja (R0) jednadžba [22]. Komponente jednadžbe vektorskog kapaciteta su sljedeće: brzina grizenja vektora (a), gustoća vektora (m), vjerojatnost dnevnog preživljavanja vektora (p), kompetentnost vektora (b) i vanjsko razdoblje inkubacije patogena (N). Zaražena osoba ugrize se ma vektora svaki dan. Od ovih ma zalogaja, samo udio b je zarazan na vektor, dajući ukupno mab vektori zaraženi primarnim slučajem. Udio vektora koji su preživjeli vanjsko razdoblje inkubacije je str N , tako map N vektori postaju zarazni. Svaki od ovih zaraznih vektora tada preživi u prosjeku 1/−ln (p), a za to vrijeme ugrize ljude brzinom od a ugriza dnevno, što ukupno čini a/−ln (p) ugrizi. Dakle, postoje map N zarazni vektori koji proizlaze iz primarnog stvaranja slučaja a/−ln (p) infektivni ugrizi na osjetljivim domaćinima, što rezultira sljedećim vektorskim kapacitetom: ma 2 bp N /−ln (p). Stoga će svaka komponenta jednadžbe imati određeni utjecaj na sposobnost komaraca da prenose patogene. Kao takvo, ciljanje bilo koje od ovih komponenti moglo bi rezultirati smanjenjem prijenosa patogena.

Jednadžba vektorskog kapaciteta (VC) i učinci mikrobioma na vektorski kapacitet komaraca. Mikrobiom komaraca može modulirati pet komponenti vektorskog kapaciteta. Ove komponente su gustoća vektora (m), brzina ugriza vektora (a), kompetentnost vektora (b), vanjsko razdoblje inkubacije patogena (N) i vjerojatnost dnevnog preživljavanja vektora (p). Mikrobiom može utjecati na vjerojatnost dnevnog preživljavanja vektora modulirajući sposobnost komaraca, u interakciji s drugim mikroorganizmima i utječući na otpornost na insekticide. Također može utjecati na gustoću vektora kroz učinke na rast, razvoj i reproduktivni učinak domaćina te moduliranjem njihove otpornosti na abiotički stres

Nekim komponentama jednadžbe vektorskog kapaciteta tradicionalno se posvećuje veća pozornost od drugih nastojanjima u borbi protiv komaraca. Vjerojatnost dnevnog preživljavanja i gustoće ciljani su adulticidima i larvicidima, čime je postignuto značajno smanjenje zaraznih bolesti, no pojava rezistencije na insekticide i različiti neciljni učinci ugrožavaju ove strategije [23]. Vektorska kompetencija bila je glavni fokus dizajna novih metoda upravljanja vektorima, poput izdavanja Wolbachia-zaraženi komarci radi zamjene populacije, što je pokazalo neviđen uspjeh u suzbijanju denge [24]. Međutim, malo se pozornosti pridavalo drugim aspektima biologije komaraca koji mogu imati jednak ili potencijalno veći učinak na prijenos patogena [25,26,27,28]. U tom smislu, velika raznolikost mikroba povezanih s crijevima komaraca mogla bi ponuditi nove alate za ciljanje različitih komponenti vektorskog kapaciteta [29, 30]. Međutim, kako bi se mikrobiom iskoristio za kontrolu vektora, neophodno je razumjeti kako takvi mikrobi moduliraju vektorsku biologiju. U ovom pregledu prikupljamo i razmatramo dokaze o utjecaju koji mikrobiom povezan s crijevima komaraca ima na određene komponente jednadžbe vektorskog kapaciteta. Također raspravljamo o drugim vektorskim sustavima i vodimo se onim što možemo zaključiti iz drugih modela insekata. Na kraju, crpimo iz bitnog Wolbachia baze znanja kada nedostaju dokazi o tome kako mikrobi povezani s crijevima utječu na svojstva relevantna za vektorski kapacitet komaraca.


Utjecaj ekologije uzgajališta na bakterijsku mikrobiotu komaraca

Podrijetlo mikroba koji naseljavaju komarce i uloga okoliša u akviziciji mikroba pitanja su o kojima se dugo raspravljalo [16]. Ovaj aspekt je bitan za definiranje dinamike mikrobnih zajednica u holobionu komaraca. Većina dosadašnjih istraživanja o akviziciji mikroba kod komaraca bila je usredotočena uglavnom na bakterijsku komponentu.

Nedavna istraživanja potvrdila su da se značajan dio bakterija koje naseljavaju komarce stječe tijekom faze vodenog života, putem staništa vodenih larvi. Sastav mikroba i značajke okoliša na mjestima gniježđenja mogu djelomično objasniti različite obrasce kolonizacije bakterija u nezrelim i odraslim fazama komaraca (slika 1). Ovi učinci vjerojatno naglašavaju međuvrsne varijacije u mikrobioti zbog tropizma staništa različitih vrsta komaraca. Duguma i sur. [17] pokazali su neke obrasce povezanosti između sadržaja hranjivih tvari i mikrobnog sastava u staništima ličinki i bakterijskih zajednica povezanih s Culex nigripalpus odrasle osobe. Dok su komarci koji potječu sa staništa bogatih hranjivim tvarima bili povezani s pripadnicima reda Clostridiales, oni iz staništa s niskim sadržajem hranjivih tvari bili su povezani s članovima reda Burkholderiales. Specifičan profil zajednice, ovisno o čimbenicima okoliša, također je povezan s sastavom bakterija u Anopheles gambiae [18]. Zanimljivo je da je pokazano da je razlika u bakterijskoj raznolikosti ličinki različitih vrsta komaraca koje dijele isto mjesto gniježđenja manja od razlike ličinki sličnih vrsta koje žive na različitim mjestima sakupljanja [19]. U Anopheles coluzzii i An. gambiae, neke bakterijske zajednice dijele se između ličinki četvrte godine, vode staništa larvi i odraslih [20]. Druga međuvrsna usporedba pokazala je da su bakterijske zajednice prisutne u vodenim staništima larvi i u crijevima ličinki međusobno slične i da se razlikuju od bakterijskih zajednica odraslih crijeva [21]. Slično, samo su Firmicutes i Actinobacteria phyla uobičajeno pronađeni u obje vrste Ae. aegypti ličinke i vodene ekosustave, s većom raznovrsnošću bakterija u vodi nego u ličinkama [22]. To sugerira da iako je bakterijska zajednica dobivena iz vode, crijeva insekata su selektivnije stanište za bakterije. Ta se selektivnost može objasniti fizikalno -kemijskim uvjetima prisutnim u crijevima (npr. Alkalni pH, redoks potencijal, razina kisika ispod 5%itd.), Kao i drugim čimbenicima poput imunološkog odgovora, peristaltike ili prisutnosti litičkih enzima ili mikrobnih interakcija . Štoviše, nalazi drugih studija ukazuju na to da neke bakterije koje se prenose ličinkama perzistiraju kod odraslih osoba (slika 1). Zanimljivo je da je Thorsellia rod je otkriven u nezrelim (ranim i kasnim stadijima larve i kukuljicama) iu odraslim fazama Culex tarsalis [23]. U Ae. albopictus, neke bakterije iz obitelji Micrococcaceae, Pseudomonadaceae i Staphylococcaceae zajedničke su ličinkama, odraslim mužjacima, kao i ženkama hranjenim šećerom i krvlju [24].

Vennovi dijagrami koji prikazuju preklapanje sastava bakterija između vrsta komaraca, razvojnih faza i staništa. a Broj specifičnih i uobičajenih svojti bakterijskih svojti između ličinki komaraca, staništa i odraslih jedinki Aedes japonicus, Aedes triseriatus i Anopheles gambiae [20, 21]. b Broj svojti bakterija specifičnih i zajedničkih za ličinke Anopheles gambiae, Culex pipiens, Culex nigripalpus, Aedes aegypti i Aedes japonicus [17, 18, 20, 22, 23, 27]. c Broj svojti bakterija svojstven i uobičajen za odrasle osobe Anopheles gambiae, Anopheles stephensi, Culex nigripalpus, Aedes albopictus i Aedes aegypti [17, 18, 20, 21, 23, 24, 27, 29,30,31,32,33, 35,36,37, 39]. Dodatna tablica prikazuje detaljnije identifikaciju bakterijskih vrsta/rodova u vrstama komaraca [vidi Dodatnu datoteku 1]

Općenito, ovi rezultati impliciraju da postoji kontinuitet bakterija od vodenog okoliša do nezrelih stadija i odraslih komaraca, što pokazuje preklapanje u sastavu bakterija između vode, ličinki i odraslih osoba [20, 25] (slika 1). Suprotno dosadašnjim pretpostavkama [26], bakterijski klirens tijekom metamorfoze komaraca s kukuljica na odrasle osobe ne bi bio potpun, što jasno sugerira da će podskup takve bakterijske mikrobiote stečene u okoliš biti dio sastavnih dijelova stanica holobionta.


Kakav bi bio učinak uklanjanja komaraca iz ekosustava?

CDC je rekao da je do sada u SAD-u bilo više od 100 primjera Zike, što me podsjetilo da postoji tvrtka Oxitec koja se bavi marketingom genetski modificiranih komaraca koji bi eliminirali populaciju komaraca uzgojem u područjima sklonim bolestima koje prenose komarci.

Je li netko upoznat s ishodima/rezultatima dosadašnjih napora na mjestima gdje su testirani? Jesu li populacije komaraca eliminirane? Jesu li se relevantne stope infekcije smanjile? Je li bilo drugih vidljivih oštećenja okolnog ekosustava?

Općenito, koliko su komarci važni za svoje ekosustave? Razlikuje li se značajno od mjesta do mjesta tako da je na ovo pitanje nemoguće odgovoriti ili postoje općenito stvari koje možemo reći o očekivanim učincima uporabe Oxitec 's komaraca (ili nekom drugom obliku širokog uklanjanja komaraca) na okolne prostore ekosustava?

Nažalost, nije doista jasno kakav bi učinak bio, i vjerujem da trenutno prevladava mišljenje da bi bilo bolje pogriješiti na strani opreza kontrolirajući njihov broj, a ne potpuno ih iskorijeniti. Zika virus se širi putem vrste komaraca Aedes aegypti i Aedes albopictus. Postoji preko 3000 različitih vrsta komaraca, koji se obično ne hrane ljudima, obično preferiraju konje, goveda ili druge velike sisavce. Neki se čak hrane i člankonošcima i drugim beskralježnjacima. Budući da se Zika i drugi flavivirusi prenose samo putem Aedes komarci, možda biste mogli iskorijeniti nekoliko ovih vrsta bez većeg utjecaja. Druge bolesti, poput malarije, prenose drugi rodovi komaraca. Da biste uklonili komarce kao vektor prijenosa bolesti, morali biste izvaditi brojne rodove, i to kada biste mogli naići na problem koji potencijalno narušava ekosustave. Članak s vijestima koji svi vole citirati po ovom pitanju jednostavno je to - članak s vijestima i ne treba ga shvatiti kao evanđelje kada zaključi da se komarci mogu sigurno iskorijeniti.

Komarce jedu uglavnom drugi insekti i ribe, ali također doprinose prehrani nekih ptica i sisavaca. Potpunim uklanjanjem komaraca uklanjate izvor hrane (u različitom stupnju) za mnoge životinje. Studije poput ove pokazale su smanjenje broja ptica koje se rađaju nedugo nakon što je područje poprskano kako bi se smanjila populacija komaraca. To je utjecajno jer ne zahtijeva potpuni gubitak populacije da bi se stvorila neravnoteža u prehrambenom lancu. To bi vjerojatno također rezultiralo povećanjem broja drugih krilatih štetočina koje bi inače kontrolirala zdrava populacija ptica. Ovakve smetnje mogle bi imati potencijalno nepredviđene i dalekosežne učinke na druge vrste.

Osim toga, samo ženke komaraca zapravo ujedaju ljude. Utvrđeno je da su muški komarci važni u oprašivanju nekih vrsta biljaka, što se također spominje u gornjem članku s vijestima. Njihovo uklanjanje moglo bi potencijalno biti štetno za ekosustav, ali bi također moglo utjecati na proizvodnju tropskih usjeva, što ima negativan gospodarski utjecaj.

Također nije potrebno potpuno iskorijeniti komarce kako bi se značajno smanjilo njihovo globalno zdravstveno opterećenje. Ova studija pokazuje da je vjerojatno nepotrebno pokušavati upravljati svim vodenim staništima kako bi se smanjilo opće opterećenje bolestima, nego samo liječiti odabrane. Štoviše, razvijaju se nova cjepiva protiv malarije i drugih bolesti koje prenose komarci. Kandidat za cjepivo RTS, S/AS01, iz GlaxoSmithKline Biologicals pokazao je 39% učinkovitost u ispitivanju faze 3, daleko bolje od brojnih drugih kandidata. Jedini način da odete odavde je gore.

Kao što ste spomenuli, komarci se također mogu genetski modificirati kako bi bili sterilni i smanjili ukupnu populaciju uzgojem, ili čak bili otporni na određene bolesti, poput malarije. Ovaj i drugi pristupi, poput prskanja površina insekticidima, zasigurno su mnogo sigurniji i pouzdaniji pristupi poboljšanju javnog zdravlja od potpunog iskorjenjivanja komaraca, a već se pokazalo da djeluju na smanjenje ukupnog zdravstvenog opterećenja. Jedna od metoda pomoću koje bi se genetska modifikacija komaraca mogla postići je tehnologija genskog pogona, što bi, naravno, zahtijevalo opsežna ispitivanja prije uvođenja, jer nosi vlastiti rizik da ih druge vrste nekako pokupe i dalje šire. Genetski pogoni nesumnjivo su kontroverzni 1, 2 i moguće je da možda nikada neće biti dovoljno sigurni za upotrebu na ovaj način. Sustav Oxitec se još uvijek razvija, ali su korištene i druge negenetske metode sterilizacije insekata za uspješno iskorjenjivanje ili smanjenje određene populacije muha.

Nažalost, ne znamo točno što bi iskorjenjivanje komaraca učinilo ekosustavu. Barem po mom mišljenju, a znam da postoje i ekolozi koji slično vjeruju, bilo bi bolje da se poslužimo drugim metodama kontrole, jer se od nas mora griješiti sa oprezom i biti odgovorni prema okolišu u kojem živimo.


Prevencija

U slučaju komaraca, gram prevencije zaista vrijedi pola kilograma lijeka. No, budući da su komarci češći u toplijim sezonama kada želite provesti vrijeme na otvorenom, morate poduzeti neke mjere opreza:

  • Razmislite o vremenu. Komarci su najaktivniji - i najvjerojatnije će ugristi - tijekom izlaska i zalaska sunca. Ako je moguće, izbjegavajte izlaske u to vrijeme.
  • Koristite repelente. Na tržištu postoji nekoliko vrsta sredstava protiv komaraca - uključujući prirodne mogućnosti - ali DEET se pokazao najučinkovitijim u držanju komaraca i drugih insekata koji grizu.
  • Nosite odgovarajuću odjeću. Dugi rukavi i prskanje odjeće repelentom mogu biti vrlo učinkovita zaštita, ali imajte na umu da je permetrin repelent za odjeću koji se nikada ne smije nanositi izravno na kožu.
  • Riješite se stajaće vode. Komarci se razmnožavaju u stajaćoj vodi, pa će uklanjanje kanti, lokvi ili neobrađenih bazena pomoći smanjiti komarce u vašem području.
  • Instalirajte ili popravite prozorske zaslone. Mrežasti zasloni omogućuju ulazak zraka, ali štite bube.
  • Očistite potencijalna uzgojna područja. Komarci koji se izlegu u susjedovom dvorištu vjerojatno će vas ugristi kao i njih. Projekt čišćenja naselja u rano proljeće može pomoći u uklanjanju stajaće vode i uzgajališta komaraca.

Sterilizacijski skeleti

Komarci su jedan od najvećih neprijatelja čovječanstva, za koje se procjenjuje da šire infekcije na gotovo 700 milijuna ljudi godišnje i uzrokuju više od milijun smrtnih slučajeva.

Ugledni profesor UC Santa Barbara, Craig Montell, napravio je iskorak u jednoj tehnici za kontrolu populacije Aedes aegypti, komaraca koji prenosi dengu, žutu groznicu, Ziku i druge viruse. Studija, objavljena u Zbornik Nacionalne akademije znanosti, dokumentira prvu upotrebu uređivanja gena CRISPER/Cas9 za ciljanje specifičnog gena vezanog za plodnost kod mužjaka komaraca. Istraživači su tada mogli zaključiti kako ova mutacija može potisnuti plodnost ženki komaraca.

Montell i njegovi koautori radili su na poboljšanju prakse suzbijanja vektora koja se naziva tehnika sterilnih insekata (SIT). Kako bi upravljali populacijom, znanstvenici uzgajaju mnogo sterilnih muških insekata. Zatim oslobađaju ove mužjake u broju koji nadmašuje njihove divlje kolege. Ideja je da se ženke koje se pare sa sterilnim mužjacima prije nego nađu plodnu same postanu neplodne, čime se smanjuje veličina sljedeće generacije. Ponavljanje ove tehnike nekoliko puta može srušiti populaciju. Štoviše, budući da je svaka generacija manja od prethodne, oslobađanje sličnog broja sterilnih mužjaka s vremenom ima jači učinak.

SIT se pokazao učinkovitim u suzbijanju brojnih poljoprivrednih štetočina, uključujući medonošca (mediteranska voćna muha), velikog štetnika u Kaliforniji. Također je pokušano s komarcima A. aegypti, koji potječu iz Afrike, ali su od tada postali invazivni u mnogim dijelovima svijeta, uglavnom zbog klimatskih promjena i globalnih putovanja.

U prošlosti su znanstvenici koristili kemikalije ili zračenje za sterilizaciju mužjaka A. aegypti. "Postoji dovoljno gena koji utječu na plodnost pa će samo nasumičan pristup miniranja velikog broja gena uzrokovati da muškarci budu neplodni", rekao je Montell, profesor molekularne, stanične i razvojne biologije iz Duggana. Međutim, kemikalije ili zračenje utjecali su na zdravlje životinja do te mjere da su bili manje uspješni u parenju sa ženkama, što potkopava učinkovitost tehnike sterilnih insekata.

Montell je zaključio da mora postojati ciljaniji pristup s manje kolateralne štete. On i njegove kolege, uključujući i prve autore Jieyan Chen i Junjie Luo, krenuli su u mutiranje gena u komaraca koji je posebno uzrokovao mušku sterilnost, a da pritom nije utjecao na zdravlje kukaca. Najbolji kandidat kojeg su pronašli je mutacija b2-tubulina (B2t) srodnog gena B2t u voćnih mušica uzrokovana je muškom sterilitetom.

Koristeći CRISPER/Cas9, istraživači su izbacili B2t u mužjaka A. aegypti. Utvrdili su da mutirani mužjaci ne proizvode spermu, ali za razliku od prethodnih napora, sterilni klinovi su inače bili potpuno zdravi. Bilo je nekih rasprava o tome je li spermija - iako neispravna spermatozoida sterilnih mužjaka - potrebna da bi ženke komaraca postala neplodna ili je sve što je potrebno za prijenos sjemene tekućine.

U jednom su eksperimentu istraživači uveli 15 mutiranih mužjaka u skupinu od 15 ženki na 24 sata. Zatim su zamijenili B2t mužjake za 15 mužjaka divljeg tipa i ostavili ih tamo. "U osnovi su sve ženke ostale sterilne", rekao je Montell. Ovo je potvrdilo da B2t mužjaci mogu potisnuti žensku plodnost bez stvaranja sperme.

Zatim je tim krenuo utvrditi kako je vrijeme utjecalo na učinak. Izlagali su ženke mutiranim mužjacima različito dugo. Znanstvenici su primijetili malu razliku nakon 30 minuta, ali je plodnost žena nakon toga brzo pala. Montell je primijetio da su se ženke kopulirale u prosjeku dva puta čak i tijekom prvih 10 minuta. To mu je pokazalo da se ženke moraju pariti s mnogim sterilnim mužjacima prije nego što i same postanu neplodne.

Kombiniranjem ženki s B2t mužjacima četiri sata smanjuje se plodnost ženki na 20% normalne razine. Nakon osam sati brojke su se počele izjednačavati oko 10%.

Uvidom u vremenska ispitivanja tim je pokušao približiti SIT u prirodnijim uvjetima. Dodali su različite omjere B2t i mužjaka divljeg tipa u isto vrijeme populaciji od 15 ženki tijekom jednog tjedna, te zabilježili plodnost žena. Omjer od oko 5 ili 6 sterilnih mužjaka prema jednom mužjaku divljeg tipa smanjio je plodnost ženki za pola. Omjer 15 prema 1 potisnuo je plodnost na oko 20%, gdje se poravnao.

Populacije Aedes aegypti lako bi se mogle vratiti nakon pada plodnosti od 80%, primijetio je Montell. Uspjeh SIT-a dolazi iz naknadnih, uzastopnih oslobađanja sterilnih mužjaka, pri čemu će svako oslobađanje biti učinkovitije od prethodnog jer sterilni mužjaci čine sve veći udio populacije.

Montell planira nastaviti s istraživanjem ponašanja parenja komaraca i plodnosti. Smišljaju način održavanja zaliha mužjaka B2t pa su sterilni samo u divljini, a ne u laboratoriju. Osim toga, karakteriziraju muško parenje kako bi otkrili nove načine za suzbijanje populacija komaraca.

"Postali smo jako zainteresirani za proučavanje mnogih aspekata ponašanja u Aedes aegypti jer ti komarci utječu na zdravlje toliko mnogo ljudi", rekao je Montell, koji je u prošlosti proveo mnoga istraživanja koristeći voćne mušice. "Svake godine dolazi do pandemije bolesti koje prenose komarci."

"Kad je CRISPER/Cas9 izašao prije nekoliko godina, samo je ponudio nove mogućnosti da radite stvari koje prije niste mogli", nastavio je. "Dakle, učinilo nam se pravo vrijeme da počnemo raditi na Aedes aegypti."

Odricanje: AAAS i EurekAlert! ne snose odgovornost za točnost priopćenja objavljenih na EurekAlert! davanjem doprinosa ustanovama ili za korištenje bilo kojih informacija putem sustava EurekAlert.


Što bi se dogodilo da eliminiramo svjetske komarce?

Komarci: Možemo li ih se riješiti i što bi se dogodilo da to učinimo? izvorno se pojavio na Quori: mjesto stjecanja i razmjene znanja, osnažujući ljude da uče od drugih i bolje razumiju svijet.

Odgovor Matana Shelomija, Entomologija, Biologija, Evolucija, na Quori:

Čudno je čuti ljude tako željne uzrok izumiranje jednom umjesto da ga spriječite, zar ne? Ova mržnja nije samo zato što su komarci dosadni. Komarci su vjerojatno najsmrtonosnija životinja na svijetu za ljude, uključujući i druge ljude. Oni se šire, ili vektor, bolesti poput malarije, žute groznice, dengue, chikungunye, virusa Zapadnog Nila i virusa Zika, koje zajedno uzrokuju više smrti svake godine nego rat i ubojstva zajedno. Uklanjanjem ovih bolesti spasili bi se milijuni života, a uklonila bi se i mnogo patnje i invaliditeta. Bez komaraca ove bi bolesti prestale postojati ... ali zašto je to tako?

Moramo li ubiti svi komarci?

Ne, jer nisu svi loši. Komarci su muha u obitelji Culicidae, a ima ih preko 3500 vrsta! Ženke polažu jaja obično u mirnu vodu, bilo što, od plitkog jezerca do saksije, kupališta ili lokve. Ličinke žive u vodi, jedu mikrobe i male čestice ili alge. Kukulje se u vodi, a odrasli komarac na kraju izađe s vodene površine i odleti.

Što jedu odrasli komarci? Većina su vegetarijanci. Piju cvjetni nektar, biljni sok i voćne sokove, a nikada ne piju krv. Ubijanje ovih vrsta nije potrebno: zapravo je kontraproduktivno. Više od 90 vrsta jednog takvog bezopasnog roda, Toksorhinhiti, također poznati kao "slonovski komarac" zbog svoje velike veličine, saveznici su našeg uzroka: njihove ličinke jedu druge ličinke komaraca! Budući da su od pomoći, trebali bismo se pobrinuti da sve strategije koje koristimo za ubijanje loših komaraca ostave ove nježne divove na miru.

Od komaraca koji sišu krv, samo se nekoliko (200 -tinjak) hrani ljudima. Drugi se hrane samo pticama ili gušterima ili manjim sisavcima, a mnogi od onih koji grizu ljude radije bi se hranili nečim drugim. Od onih koji se mogu hraniti ljudima, ne nose svi ljudske bolesti, pa čak ni kod vrsta koje to čine, nisu svi sojevi učinkoviti prijenosnici. Također, različite vrste nose određene bolesti. Na primjer, Plazmodij, protozojski parazit koji uzrokuje malariju, gotovo isključivo šire komarci iz roda Anofeles. Od oko 460 vrsta Anofeles komarac, samo stotinjak njih zapravo može nositi pet -tinjak vrsta Plazmodij koji inficiraju ljude [od preko 200 vrsta Plazmodij koji inficiraju druge životinje]. Od ovih stotina, samo tri ili četiri desetine su dovoljno dobri vektori koji predstavljaju opasnost za ljude, a samo nekolicina njih zapravo preferira ljude kao izvor krvi, a samo pet nosi Plasmodium falciparum, jedina vrsta malarije odgovorna za najgore simptome i većinu smrtnih slučajeva. Od ovih, najgore je Anopheles gambiae, although this is technically a species complex of at least seven different species… but that's another story. In summary, if you want to destroy malaria, there are only a few species that matter the most, and focusing on An. gambiae is the priority. Killing this one species [complex] alone would save millions.

A few other genera carry other disease agents, namely arboviruses (short for arthropod-borne viruses). Many species in the genus Aedes, but especially Aedes aegypti i Ae. albopictus, vector arboviruses such as dengue virus, yellow fever virus, Zika virus, chikungunya virus, West Nile Virus, La Crosse virus, and some animal viruses such as Western equine encephalomyelitis virus. Many of these viruses are also spread by species in the genus Culex, which also spreads bird malaria, and the genus Culiseta, which rarely bites humans, and Ochlerotatus [there is controversy over this genus name that I won't get into here]. Rod Haemagogus spreads yellow fever and some rarer viruses called Mayaro and Ilheus viruses. Rod Mansonsia can spread some arboviruses, but are more important for spreading roundworms that cause filiariasis in Asia and the Pacific. The other genera also have roundworm-vectoring species, responsible for the spread of heartworm in dogs and other animals and lymphatic filiariasis and elephantitis in humans.

Why are some species better vectors than others? The answer is because mosquitoes don’t just carry diseases: they get sick from them. When the mosquito swallows infected blood, its own midgut gets infected. The pathogens replicate in the midgut and burst out into the body cavity, where they eventually infect the salivary glands. The whole process takes up to two weeks depending on the disease. When mosquitoes bite their next victim, the pathogen is injected with the saliva. This is one reason why HIV, the virus that causes AIDS, is not vectored by mosquitoes: it cannot infect the mosquito midgut and just gets digested away. Different mosquito species may be immune to certain pathogens, have resistant midguts or resistant salivary glands, or may simply die of natural causes before the pathogen can complete its replication cycle and reach the salivary glands. Infected mosquitoes do sometimes have shorter life spans, so evolution keeps the diseases in check: they cannot kill the mosquito before they've finished incubating and have been injected into a new host.

In summary, we don't need to kill all the mosquitoes. Just the vector species.

What do mosquitoes do for the world?

Do mosquitoes serve a purpose other than spreading disease? More importantly, do the vector species have a role that makes them worth keeping around?

Let’s start with the larvae. Living in the water and eating detritus, they do keep the water somewhat clean, but so do lots of other organisms that aren't disease vectors. So mosquito larvae don’t eat anything important… except for the Toksorhinhiti larvae that eat other mosquito larvae, and we’ve already agreed that we’ll be sparing this genus from genocide.

What eats the larvae? Other aquatic larvae do, such as dragonfly and damselfly nymphs, as well as some turtles and large tadpoles and fish. The most famous predators of mosquito larvae are Gambusia affinis i Gambusia holbrooki, better known as mosquitofish. Native to the USA, they are commonly introduced to ponds and pools as a mosquito control, with some governments giving them out for free, with the assumption that they will eat the mosquito larvae rather than anything else. This worked wonders in some parts of the world, especially near the Russian city of Sochi, formerly a malaria hotspot a statue of the fish was erected there in gratitude in 2010.

However, the assumption is incorrect, and the common name a misnomer. G. holbrooki actually prefers plankton, algae, and detritus [the same foods as larval mosquitoes], and mostly switches to invertebrates like mosquito larvae when it really has no choice. G. affinis is a better predator, capable of eating half to one-and-a-half times their own body weight in mosquitoes every day. However, they cannot live on mosquitoes alone, but actually suffer malnourishment and stunted growth, and must eat other foods too like plankton and other insects. Despite their name, they only eat mosquitoes as a small part of their normal diet. Worse, they are extremely aggressive towards other fish, which themselves are often just as effective at eating mosquitoes. In Australia, mosquitofish deliberately introduced in the 1920’s and 30’s bullied or outcompeted native fish and frogs and reduced their numbers to such an extent that mosquito numbers actually went gore, because there were fewer predators overall. That the fish and frogs and native insects being killed or eaten by the mosquitofish were themselves important species now threatened by extinction meant introducing the mosquitofish would have been a bad idea even if they did fight mosquitoes. Sochi was spared this disaster because they didn’t have many native fauna to be threatened by the mosquitofish to begin with. The possibility exists that introducing another fish, like a catfish or even goldfish, would have worked there just as well. Jasno, Gambusia is not a reliable ally in the global mosquito extinction campaign, but on the other hand we need not worry about losing fish if the mosquito larvae die off, since no fish [or other animal] depends on them exclusively.

What about adult mosquitoes? They’re food for an even greater diversity of creatures, from fish and frogs to salamanders and lizards to venus fly traps and birds and bats, not to mention other insects… but ne, by the way, the "mosquito-hawk." That's a name given to crane flies, which not only don't eat mosquitoes but also don't eat anything at all: the adults have short lifespans and don't bother feeding. The insects that do eat adult mosquitoes include dragonflies and damselflies, with the benefit that their aquatic nymphs also eat the aquatic mosquito larvae and pupae. They are the mosquitoes’ lifelong nemesis.

Could these natural predators be used to eradicate mosquitoes, and would eradicating mosquitoes harm these predators? No and no. Again, the mosquito is not the only animal eaten by any of these creatures. A great example is the Purple Martin (Progne subis), a rather handsome, insectivorous, American bird commonly promoted as a viable biocontrol against mosquitoes, but possibly overhyped. Multiple studies have looked at its feeding habits, and found that mosquitoes are not a big part of its diet, that their feeding ranges and times do not overlap with when and where vector mosquitoes are active, and that Purple Martin releases have not had big effects on local mosquito populations [though some contradictory studies exist]. Also, like Gambusia, the Purple Martin can make the situation worse because it eats other predatory insects like dragonflies, as well as other insects across the harmful/helpful spectrum from beetles to bees. Dragonflies themselves will also happily eat honeybees and butterflies in addition to mosquitoes, gnats, midges, and flies. The same applies for bats, where mosquitoes may make up less than 1% of their diet. Can you blame these predators? Mosquitoes are tiny, barely a mouthful, while a fat beetle or chubby moth is much more nutritious snack.

What if these alternative food sources did not exist? Is there any part of the world where mosquitoes are a dominant insect? Yes: the arctic. While most insects prefer warm weather, and the tropics have the greatest insect diversity overall, the arctic tundra actually has the biggest mosquito problems in the world, because the land there is a perfect incubator for mosquitoes. The soil is near frozen all winter, but in the summer it thaws, making entire fields one gigantic breeding ground for mosquitoes. Mosquito swarms reach biblical proportions in these regions, forming thick, dark clouds of insects. Scientists believe the mosquitoes su a critical part of the diet of birds in these regions… but others disagree, claiming native midges (related flies from the family Chironomidae) are actually a bigger part of the native birds’ diets and would fill the gap left by mosquitoes. Thus the birds of the arctic are the most likely and perhaps only creatures that mogao lose a major food source without mosquitoes. Fortunately, the dominant mosquito species in the arctic are Aedes impiger i Aedes nigripes, neither of which vectors human diseases. So if our goal is to fight vector species, we could leave the arctic alone.

What about pollination? Are any plants mosquito-pollinated? Yes, many, but most of these are pollinated by other insects as well, such as goldenrod. A few plants do exist that are preferentially mosquito pollinated, meaning other insects can pollinate them but mosquitoes are the most common and most efficient. All are orchids, namely cold-temperature ones. Primjer je Platanthera obtusata, the blunt-leaved orchid found across the Arctic, pollinated by mostly female Aedes mosquitoes as well as a few moths. It attracts mosquitoes by giving off a faint scent, detectable by mosquitoes but not our own noses, that is very similar to human body odor. The related Platanthera flava is also pollinated by Aedes primarily and small moths secondarily. Ostalo Platanthera species are pollinated by mosquitoes secondarily and other insects primarily, or are mostly self-pollinating and rarely require insect help, and a few other orchid species have similar cases. Loss of some of these orchids is thus a risk of loss of mosquitoes. However, none of the orchids are important to the ecosystem itself, nor are they important to humans: the world will live on without them. That’s not to say the rather large problem of orchid extinctions isn’t serious, but the problem of insect-vectored disease is arguably worse.

What are the risks of eradicating mosquitoes?

As you noticed, there are no keystone species in mosquitoes. No ecosystem depends on any mosquito to the point that it would collapse if they were to disappear. An exception svibanj be the Arctic, but the species there are non-vectors and thus can be left alone.

Granted, we are making assumptions here. We certainly do not know all the myriad ways all mosquitoes interact with all life forms in their environment, and there may be something we are overlooking. Non-target extinction isn’t the only problem: there’s also the possibility that the gap (technically an ecological niche) left behind by mosquitoes will be filled by something even more annoying, though likely non-vectoring. The worst scenario is one vector mosquito species will replace another, and the most likely scenario is mosquitoes will be replaced by midges. They also have aquatic larvae and the females of some also blood-feed, some on humans. The combination of fewer mosquito competitors and possibly fewer predators of mosquitoes could mean an explosion of midge populations. On the other hand, the predators now reliant on mosquitoes may eat more midges instead, causing the populations to reach a stable equilibrium after a while. Are midges dangerous? Those in the family Chironomidae do not bite, but those in the family Ceratopogonidae do, and not only can their bites be itchy for as long as week, a few do vector human and animal diseases [though not human malaria or yellow fever as far as we know].

Another surprising way mosquitoes can affect the ecosystem comes, again, from the arctic. Mosquitoes control the migrations of woodland caribou (Rangifer tarandus caribou). Their massive herds in Canada are always on the move to find food, but in the summer they travel a lot more, covering greater distances and moving to higher ground, sometimes avoiding the best feeding sites, because they are trying to avoid the gigantic swarms of mosquitoes that plague the Arctic regions in the summer! All the time spent running and not eating means they build up less fat that they would need for the cold winters, which can often mean death. Killing off these mosquitoes would change the historic caribou historical migration routes, with unpredictable consequences. On the other hand, caribou populations today are a fraction of what they once were, down to several thousands from several hundreds of thousands due primarily to human habitat destruction, so more caribou would be a good thing. The caribou are clearly are bothered by mosquitoes, losing up to a liter of blood a week during the worst outbreaks, so if asked I’m sure they’d vote for eliminating mosquitoes, and given their population size and herd mentalities they’d likely come out to vote in large numbers.

Truly worst-case scenarios are unlikely, considering that we’ve eradicated many malaria mosquitoes from parts of Europe and North America without trouble, but they are still possible, so any extinction or extirpation [a local extinction from a smaller area, not the entire planet] has unforeseen risks. The question is: are the risks of može biti altering an ecosystem worth human life, and how much? We are not arguing over whether or not to save the panda, but to eliminate the greatest killers humanity has ever known. Given that arboviruses and malaria currently su killing or affecting millions, to not eradicate the vector mosquitoes responsible could only be justified if the expected environmental effects would be similarly damaging. We cannot poison an entire rainforest to fight yellow fever, because millions of people depend on that rainforest for food, medicine, wood, employment, clean water, and clean air: the cure would be worse than the disease [literally] and affect more people. On the other hand, say we eliminate Aedes aegypti and a salamander species and an orchid are eliminated along with it: that is a trade we can live with, and by “we” I mean the millions who will no longer die from yellow fever. The other extinctions will be a tragedy, yes, but the loss of yellow fever will be a triumph worthy of the Nobel Peace Prize. Compared to the losses of the dodo and the Tasmanian tiger, which came with no benefit to society and are thus completely unfortunate, the benefits of the loss of Ae. aegypti ili An. gambiae would outweigh even the most pessimistic estimates of costs.

How could we kill all the world's vector mosquitoes?

Because tampering with ecosystems is so tricky, it is important not to use methods that are too broad. It’s hard enough to predict the effects of killing one species: imagine having to factor in the loss of any species slučajno killed in the process… assuming we can even predict them all! So pesticides are out: they have non-target effects, and, besides, they won't work on a global scale. Aerial sprays won't hit the mosquitoes that like to bite indoors, and putting oils or insecticides in breeding sites won't catch the many, many tiny breeding sites in peoples' properties: everything from a tree hollow to a bit of rainwater sitting in a discarded plastic bag is a potential mosquito breeding site. That's why public participation is important in mosquito control: everyone must do their part to clear the breeding sites in their backyards. Alas, if even one is missed, the mosquitoes will return.

No, if we are going to eradicate mosquitoes worldwide, we need a method that is species specific, unstoppable, and inescapable. Something guaranteed, by way of design, to affect samo the target organism, and to be impossible to adapt to or evolve resistance against. We need autocide, where the species is unwittingly responsible for its own death. Is such a thing even possible?

It is, and it has been done. The New World screw-worm fly (Cochliomyia hominivorax), also known as the screw-worm, is a parasitic fly whose maggots infest the healthy tissue of warm-blooded mammals. This includes humans, but the bigger problem is cattle, where the worms cause death within ten days. In the 1950’s, losses in the USA due to screw-worm were over US$200million a year. Something needed to be done, but pesticides were not working. Scientists studied the screw-worm intensively, including a $250000 study partly on the sex-lives of screw worms that was widely decried by US senators as wasteful spending of taxpayer funding. They would later eat their words with an American-grown steak and a glass of milk. It turns out that female screw-worms are monogamous, only mating once in their lifetime. Scientists Edward Knipling and Raymond Bushland reasoned that if a female screw-worm mates with a sterile male, her eggs will never hatch, and since males mate repeatedly, one sterile male can not-impregnate multiple females. Thus, if one floods an ecosystem with a large enough number of sterile males [which have no effect on cattle, because males don't drink blood or lay eggs], they will out-mate the healthy males and the number of fertile matings is reduced, instantly reducing the size of the next generation. This process is repeated constantly until eventually every female mates with a sterile male, at which point the population is wiped out… forever.

Ovaj sterile insect technique (SIT) was tested with screw-worms in the 1950’s using X-rays [later gamma rays and other techniques] to sterilize flies mass-reared on ground meat in the lab, irradiating them at the pupal stage just enough to sterilize males without making them too weak to compete with normal males. Long story short, it worked. By releasing large numbers of sterile male flies over several weeks at a time, SIT successfully eliminated the screw-worm from the USA, then Mexico, working southwards until all of North and Central America was cleared of the flies. When screw-worm was accidentally imported to Libya in 1988, sterile males were eventually brought in on December 1990 and eradicated the screw-worm in less than a year. Sterile screw-worm males are still released in Panama periodically, forming a biological wall against any females from the South. The results saved the US cattle industry alone over $20billion and counting, winning its authors the 1992 World Food Prize and being declared “the greatest entomological achievement of (the 20th) century.”

The principles of SIT make sense for safely eliminating vector species, since there are no other effects on the environment other than those caused by the loss of the species itself, and it only works on a single species at a time: SIT against Aedes aegypti won’t have an impact on Aedes impiger, let alone other genera of mosquitoes, let alone other insects, let alone mammals or people. Many mosquito females are also monogamous, so SIT could work in theory. Plus, since only the vegetarian male insects are released, one can unleash billions of these mosquitoes in an area and there won’t be a single extra insect bite. SIT has been successfully used to eradicate tsetse fly (Glossina spp., the vector of African Sleeping Sickness) in parts of Africa, and several have tried it against mosquitoes… but many failed. Efforts to eliminate Anopheles quadrimaculatus in Florida, USA over nearly a year had no effect, because the sterile males simply could not compete with the normal ones and were not chosen by mates. This happened again for Culex tarsalis in California. The problem is the radiation can weaken mosquitoes and/or lower their lifespans, so they fail to attract females. Not all insects respond well to irradiation, which limits the subjects SIT can work with.

An alternative strategy is cytoplasmic incompatability, which sounds more complex than it is. Instead of radiation the mosquitoes are infected with a bacteria called Wolbachia that lives inside insect cells, including egg and sperm cells. Kada Wolbachia-infected sperm combine with uninfected eggs, the egg dies. Guaranteed. Culex quinquefasciatus was successfully eliminated from the city of Okpo in Burma in 1967 in 9-weeks with this method. However, this technique won’t work if the wild mosquitoes takođerare infected with Wolbachia: if both egg and sperm are infected with the same strain, or even if the egg is infected and the sperm not, the embryo lives and becomes a new male or female whose eggs will also be immune. It also doesn’t solve the problem that rearing at large densities in a facility is itself stressful: studies with Anopheles gambiae showed those reared at higher densities were less like to win mates than those reared at lower or natural densities. Large numbers of mosquitoes need to be produced cheaply, but if one cuts too many costs they won’t be effective competitors for wild males and will fail to mate.

There’s another problem: since we don’t want to release blood-sucking female mosquitoes, sterile or otherwise, we need a good way to eliminate females in the lab from the irradiated pool before they are released. Unfortunately, the sex ratio for mosquitoes is 50/50, so a way of separating males and females is needed. The ones used at first could not be more primitive: Male and female mosquito pupae are slightly different colors and sizes, so someone manually or a machine with a strainer had to sort them and ensure only males get sent to be irradiated and released. Unfortunately, this does not work for Anopheline mosquitoes, because the pupa sizes overlap. Even before this point, though, money has been lost. Both males and females require the same resources in lab, so inevitably no more than half the insects raised in an SIT program will ever be released, making everything twice as expensive as it should be. Since a huge number of sterile males is needed to have any effect, these high costs are a problem for a global extermination program.

Is there some way to ensure only males are produced, or a way to kill off unnecessary females earlier? Yes, using genetic sexing strains (GSS), an old technique in which a dominant selectable marker—a gene that makes its possessor able to survive an otherwise lethal challenge— is attached to the male sex chromosome. A successful example is the aptly named MACHO: a strain of An. albimanus with an insecticide-resistance gene attached to the male chromosome (mosquitoes mostly have an XY sex-determination system like humans do, where only males have a Y-chromosome). Treating a batch of MACHO eggs with insecticide will kill 99.9% of all females, allowing a million mosquitoes per day to be released when it was used to control mosquitoes in El Salvador in the late ‘70’s. In case you are wondering, the eradication almost worked, until the mosquito immigrated back in from another country. Whatever technique we choose, it would need to be global, and in any case GSS doesn’t solve the problem that irradiation can make many mosquitoes weak competitors.

The latest advance skips irradiation all together. To se zove RIDL, short for Release of Insects carrying Dominant Lethals, invented by entomologist Luke Alphey. In RIDL, the males are not irradiated, meaning they are just as healthy and competitive for mates as wild males, but also they will produce viable eggs. So instead they carry a lethal gene that causes their larval offspring to die before reaching blood-sucking adulthood. The current form of RIDL involves a gene called tTAV (tetracycline repressible activator variant), which makes a nontoxic protein that clogs up the insect’s cell machinery so no other genes are activated, causing death. The system only works in the mosquitoes’ own cells, and the protein is degraded when eaten, so there is zero effect to animals that eat the modified mosquitoes or their larvae: It is a completely nontoxic system. “But wait, how do these mosquitoes survive to adulthood in the lab?,” you ask. The answer is Tetracycline, a common antibiotic that is also the antidote to tTAV. In the rearing facility they are fed this antidote so they can live to adulthood, but in the wild they and their offspring have no hope. RIDL is currently being used to fight mosquitoes in the southern US and South America, where they have already caused massive declines in dengue mosquitoes, and are now being deployed to stop the Zika epidemic in Brazil.

A new technique, currently developed for the Mediterranean fruit fly but perhaps one day available for vector mosquitoes, is a female-specific RIDL. In this system, males carry a gene for a protein that, in absence of the antidote, only kills females. In this system, females mated with the modified males will produce perfectly viable eggs, but the female offspring die as larvae, and only the male offspring will survive into adulthood. These males still carry the modified gene, and go on to mate with the now smaller population of females, etc. In this scenario, one need only release the males once to start a chain reaction that works through the population, reducing it with every generation.

RIDL is an amazing strategy, with no harmful effects on the environment or on non-target organisms, and it even saves humans from having to work with radiation. Alas, it involves genetic modification, which means the mosquitoes are technically a GMO, which means the usual suspects are out in force trying to stop them, some spreading rather creative lies, and the media is often unable or uninterested in sorting fact and fiction. Most stories worry about the mosquitoes flying and biting local people. Some articles claim the mosquitoes vaccinate humans against diseases, which would be amazing if it was true, but it isn’t. Others claim the mosquitoes will mutate you if they bite you, which is equally ridiculous. Some are even claiming that microcephaly isn’t caused by Zika virus but by the released mosquitoes, calling it “loose gene syndrome." Never mind that such a condition does not exist and is biologically impossible the fact that these people are willing to deny the very real problem of Zika-induced microcephaly in order to scare people off GMOs and better sell their overpriced organic produce in stores is a truly nasty appropriation of real human suffering. Fortunately, you now know the one important fact that thoroughly contradicts almost every mistake and lie ever written about insect releases: male mosquitoes don’t bite people. They don't drink blood, but actually avoid humans, and since only male mosquitoes are ever released, the idea that a released insect can harm a human is pure fiction.

Will these techniques mean we can get rid of pesticides and insecticides forever? Not quite yet. Remember that SIT and RIDL require the released males to outnumber the native males. No matter how efficiently we can rear sterile or modified males, if the wild populations are too high then these techniques will never be practical. Instead, we would need pesticides to bring down the wild populations first, to a threshold at which SIT or RIDL will work. In addition, if we want to rid the entire planet of these species, the releases would need to cover their entire ranges, which could be a massive amount of space. Still, progress is good, and even if we don’t eliminate all the vector mosquitoes in the world, we have already made a massive dent in the death toll of mosquito-vectored disease worldwide.

But wait, there's more! There is one technique that can eliminate the pathogen without harming the vector or the environment in any way, i does not require releasing or raising insects. First, let me introduce you to Chagas disease, caused by the protozoan Trypanosoma cruzi which is vectored by kissing bugs in the subfamily Triatominae, the most serious vectors being Triatoma infestans i Rhodnius prolixus. They are called “kissing bugs” because they like to bite near the mouth to suck blood. They also have the filthy habit of defecating right after they eat, and when humans scratch the bite they scrape the parasite-infested poop into the wound, infecting themselves. Charming, and also deadly, as Chagas disease can cause symptoms such as an enlarged heart. SIT has been tried in these species, but the new technique is called paratransgenesis. Rather than genetically modify the insect to make a protein (transgenesis), one modifies a symbiotic microbe that lives inside the insect instead. U slučaju Rhodnius prolixus, all individuals have a symbiotic bacteria, Rhodococcus rhodnii, that makes vitamins for them that are otherwise absent in their blood-based diet. Genetically modifying bacteria is easy, so scientists created transgenic symbionts that produce proteins toxic to the Trypanosome. If you feed Rhodnius some modified Rhodococcus, the insect now became immune to Trypanosoma cruzi, unable to vector it anymore. The bacteria can be produced in large numbers easily, bypassing a problem with insect release. Best of all, the infected adult kissing bugs pass the bacteria on to their offspring: young triatomines often eat the feces of the adults, inoculating themselves with the Rhodococcus bacteria. [In case you are wondering, the bacteria can’t survive in our bloodstream, so they can neither harm us nor help us.] The system is quite promising, involving spreading Rhodnius poop infected with modified Rhodococcus svugdje, posvuda Trypanosoma is a problem, with the end result that only the parasite dies out, while the insect is left alive, and the ecosystem is not affected at all. Paratransgenesis could be applied elsewhere, and scientists are working on developing it for other species, such using a modified fungus to make Anopheline mosquitoes immune to malaria.

You now have a clear idea of the many issues that go into whether or not a species should be eliminated, and whether or not that is even practical. If you have such a question for another insect, like fleas or roaches, maybe you can answer the question yourself! Ask yourself: Which species from the group are the real problem? What do they do in the world? Are males and females both a problem? Is SIT practical? Is there an alternative solution to the disease? If questions like these interest you, consider a career in medical entomology, epidemiology, genetics, or [of course] medicine, and maybe that Nobel Prize I mentioned will be yours.

What should we do in the meantime?

Global extermination of vector mosquitoes, whether or not it is doable and whether or not it is a good idea, is a long way off. Until then, the best strategies are to do local extirpations. If you have a pond, add goldfish, koi fish, or guppies—not necessarily mosquitofish—to eat the larvae. Insecticides are another, less ideal option, as they will kill beneficial insects too, but in emergencies they can be used as many are nontoxic to humans. That includes the ones being used in Brazil right now to fight Zika… and, no, they are not responsible for microcephaly. That claim has also been thoroughly disproven, despite what conspiracy theorists say.

For container breeding mosquitoes, remove the containers or drain them often. Keep an eye out for anything that can catch rainwater, from animal feeding bowls and flowerpots to old tires and plastic bags or tarps. The mosquitoes from these containers will bite you first, so you're doing yourself a favor in addition to the public health! Most importantly, protect yourself. Use insect repellents on your skin or clothes, and sleep under a bed net if you’re really deep in a disease endemic zone. Bed nets are most important for children, as they will suffer the hardest from diseases like malaria.

For more information on what you can do, find your local vector control or mosquito abatement district website or specialist and see what they recommend for your region.

For more on mosquito- and other insect-vectored diseases check the websites of the Center for Disease Control ( CDC - Malaria , Zika Virus | CDC ), or the US National Institute of Allergy and Infectious Diseases ( Malaria , Zika Virus ).


Rasprava

The mosquito gut microbiota plays a crucial role in the host physiology contributing to the maintenance of metabolism and immunity homeostasis, but it can also stimulate a basal immune activity impacting on mosquito’s vector capacity (Dong et al., 2009). In fact, the introduction of special bacterial isolates in mosquitoes are able to trigger their innate immune response, which correlates with a decrease in the transmission of the malaria parasite (Frolet et al., 2006).

Iako Asaia has already been described as able to stimulate the expression of some AMPs in mosquito while not being affected by phagocytosis (Capone et al., 2013), our results detailed the interactions between this bacteria and the mosquito immune system. We focused on some genes involved in Plazmodij surveillance: i) CEC1 i DEF1, belonging to AMPs gene families, are involved in the elimination of viruses, bacteria and Plazmodij (Bartholomay et al., 2004 Xi et al., 2008) ii) CTL4, encodes for C-type lectins that control the microbiota homeostasis (Hillyer, 2010 Pang et al., 2016) iii) TEP1, mainly involved in Plazmodij killing (Blandin et al., 2004 Dong et al., 2006). Posebno, CLT4 i TEP1 act against the malaria parasite as agonists and antagonists, respectively. TEP1 together LRIM1 mediate the killing of ookinetes in the midgut epithelium in contrast, CTL4 and the C-type lectin CTLMA2, protect the parasite inhibiting its melanization (Osta et al., 2004).

The supplementation of different concentrations of Asaia cells on newly emerged females showed distinctive effects in An. stephensi i An. gambiae. U An. stephensi, where the bacterium is among the dominant symbionts, Asaia quickly reached a persistent and consistent homeostasis in every experimental group. In Asa4 and Asa8 groups, the fluctuations of the bacterial load at day 1, until reaching the homeostasis at day 3, could be correlated to the up-regulation of the CTL4 gene, confirming its role in the regulation of the natural microbiota, in particular in relation to Gram-negative bacteria (Osta et al., 2004 Pang et al., 2016). Asaia density reached a constant plateau phase, remaining constant in both Asaia-challenged and control groups during later time points, possibly associated with the transcriptional induction of CEC1 i DEF1 geni.

U An. gambiae, Asaia showed to be differently regulated: likely its role as a secondary component of the natural microbiota of the African malaria vector could explain the difference in tolerance (Mancini et al., 2018). In fact, natural Asaia (sugar-fed control group) showed a gradual constant growth over time, while the infection with higher doses of cells underwent rapid fluctuations. This trend could be explained by the synergic action of the genes CEC1, TEP1, DEF1 i CTL4 in maintaining the microbiota balance. Concerning to the possible effect of bacterial challenges on Plazmodij infection, we have shown the ability of Asaia to activate the mosquito basal level immunity interfering with Plazmodij development in vivo. In fact, a significant reduction of malaria parasite load occurs five days after the infected blood meal, which coincides with stage when the parasite is present in midgut epithelium as premature oocysts (Wang and Jacobs-Lorena, 2013). Sposobnost Asaia to interfere with insect pathogens is corroborated by evidence in leafhopper as recently demonstrated by Gonella et al. (2019.). The significant up-regulation of TEP1 u Asaia-challenged An. stephensi, despite the bacterial concentrations, could be correlated to its decrease in vector competence and indicates an indirect and exploitable interplay between Asaia and the parasite. Indeed, the contribution of the microbiota of the different modulations of the mosquito immune response, seems to be correlated just to the strong presence of Asaia as demonstrated by the 16S Miseq analysis, showing it as the most abundant bacterium in mosquito administrated with Asaia enriched diets.

The reduction of the parasite load observed in An. stephensi was not conserved in An. gambiae where the lack of activation of TEP1 u Asaia-challenged samples could explain the lack of Plazmodij inhibition in An. gambiae.

Međutim, An. gambiae is not the natural vector of P. berghei, for which it is significantly more permissive than P. falciparum (Sinden et al., 2004). Štoviše, An. gambiae mosquitoes showed a different transcriptional response to infection with P. berghei i P. falciparum (Dong et al., 2006). At light of consideration, further investigations on a possible Asaia role in immune stimulation in the system An. gambiaeP. falciparum su potrebni.

Nevertheless, these findings, while providing evidences on the ability of Asaia to stimulate the basal level of mosquito immunity in two main malaria vectors, and to naturally reduce the development of malaria parasite oocysts in An. stephensi. These findings confirm and expand its potential in SC approaches, not only through paratransgenesis, but also as a promising effector for mosquito immune priming.


Zaključci

In the past 20 years, the pivotal role of the mosquito microbiota in shaping Plazmodij infection and transmission has gradually emerged. However, the tripartite interaction between the mosquito, its microbiota and the parasite is a complex relationship that still needs further investigation. In general, the microbiota was found to reduce Plazmodij infection and to impact several physiological aspects of the mosquito, notably affecting its lifespan. Surprisingly, these effects induced by the microbiota were consistent almost irrespective of the Anofeles i Plazmodij species, suggesting that this tripartite interaction is a stable system in which each component plays a role. Although our knowledge on the mosquito microbiota is continuously expanding, several aspects have not been completely elucidated yet and represent the current challenges of this field. In particular, the non-bacterial component of the mosquito microbiota has not been investigated as extensively as the bacterial one, although viruses and eukaryotes might be as relevant as prokaryotes in limiting Plazmodij infekcija. Moreover, it is not clear whether the microbiota of the reproductive track or salivary glands impacts parasite transmission or mosquito fitness. Finally, most of the functional studies conducted on the mosquito microbiota have been carried out on laboratory-reared insects, which are known to possess a different microbial community from that of field mosquitoes. Depending on the desired levels of control on experimental conditions and of relevance of microbiota composition, several experimental set ups may be used to improve the study of the mosquito microbiota.


Gledaj video: Jeftin trik: Najučinkovitije sredstvo protiv komaraca koje svi imamo u kući (Kolovoz 2022).