Aedes Ae­gypti Not The Only Mos­quito Spread­ing Zika

The Star (St. Lucia) - - HEALTH - ZIKA -

Brazil­ian sci­en­tists have found the Zika virus in the Culex quin­que­fas­cia­tus mos­quito, which is far more com­mon and wide­spread than the species pre­vi­ously iden­ti­fied as the vec­tor for the virus.

The find­ings of re­search by the South Amer­i­can coun­try’s top pub­lic health in­sti­tute, the Oswaldo Cruz Foun­da­tion (Fiocruz), sug­gest that Brazil may need to change its Zika re­sponse strat­egy, and comes as a blow to a na­tion in the grip of an out­break less than two weeks be­fore tens of thou­sands of vis­i­tors ar­rive for the Olympics.

The virus was dis­cov­ered in Culex in the north-east­ern city of Re­cife, re­garded as “ground zero” for the rash of mi­cro­cephaly cases caused by the virus. Culex is 20 times more com­mon there than Aedes ae­gypti, which un­til now has been iden­ti­fied as the main vec­tor.

Con­stan­cia Ayres, the en­to­mol­o­gist who con­ducted the re­search and who in­sisted that it was risky to fo­cus ex­clu­sively on Aedes ae­gypti as the coun­try strug­gled to re­spond to the Zika out­break, de­scribed the de­vel­op­ment as “very bad news for Brazil.”

Re­spond­ing to the an­nounce­ment, Brazil’s Min­istry of Health said that it re­mains con­vinced that Aedes ae­gypti is the most im­por­tant vec­tor. A min­istry spokesper­son added that ul­ti­mately the find­ings change noth­ing be­cause the pub­lic-health re­sponse is the same re­gard­less of the mos­quito species.

Dr Ayres and other en­to­mol­o­gists strongly dis­agree, how­ever. Culex has some sig­nif­i­cantly dif­fer­ent be­hav­iours to Aedes ae­gypti, and those habits ne­ces­si­tate very dif­fer­ent re­sponse strate­gies, she said.

For a start, Ae­gypti bites dur­ing the day, while Culex is noc­tur­nal, mak­ing bed nets, which few Brazil­ians cur­rently use, the best form of pro­tec­tion.

Ae­gypti, fur­ther­more, breeds in clean wa­ter, while Culex favours pol­luted wa­ter, like the sewage canals that snake through Re­cife.

“The only ex­pla­na­tion for how fast Zika is go­ing through Latin Amer­ica is that it’s trans­mit­ted by more than Ae­gypti – and that means you do a dif­fer­ent re­sponse, and you sam­ple for mos­qui­toes dif­fer­ently,” Fiona Hunter, a pro­fes­sor of en­to­mol­ogy at Brock Univer­sity who is work­ing on Zika trans­mis­sion in the Caribbean, told the Globe and Mail.

Doubts were also ex­pressed back in March, when sev­eral Brazil­ian and in­ter­na­tional en­to­mol­o­gists ex­pressed pub­lic con­cern over Brazil’s Zika re­sponse plan and its fo­cus on Aedes ae­gypti, say­ing it was dan­ger­ous to be fo­cus­ing all re­sources on that vec­tor with­out more ev­i­dence, es­pe­cially given that this strain of Zika was be­hav­ing in markedly dif­fer­ent ways from what had been seen be­fore else­where.

Now, in what could turn out to be a fu­tile move, the Min­istry of Health is in­vest­ing in test­ing ge­net­i­cally mod­i­fied mos­qui­toes as a Zika-con­trol strat­egy – but the species mod­i­fied is Aedes ae­gypti.

Dr Ayres said that more re­search is nec­es­sary to es­tab­lish which of the two species is the pri­mary vec­tor in Brazil in or­der to an­swer ques­tions such as whether one fo­cuses more on hu­mans than on an­i­mals, which species bites more of­ten, which trans­mits more virus in a bite and which lives longer.

Mean­while, Brazil’s Min­istry of Health re­ports 1,709 cases of con­firmed con­gen­i­tal Zika, with 102 deaths and still­births caused by the virus. More than 3,000 other cases are still un­der in­ves­ti­ga­tion.

In a wel­come lull, rates of new Zika in­fec­tion have fallen with the on­set of the Brazil­ian win­ter and less of the warm, damp weather that boosts mos­quito breed­ing.

The Culex Quin­que­fas­cia­tus mos­quito is 20 times more com­mon than Aedes ae­gypti in the north-east­ern city of Re­cife in Brazil.

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