Common stilt is the main transmitter of zika, not Aedes

Among the actions to combat the virus Zika, which became a national concern in Brazil since last year, the main one is to suppress the mosquito Aedes aegypti, considered until then, its main vector. However, recent studies show that another mosquito, very well known by Brazilians, may be the biggest transmitter of the virus: Culex, popularly known as stilt or muriçoca, and present throughout the country.


Constância Ayres (Fiocruz/PE), Stevens Rehen (IDOR/UFRJ), Rodrigo Stabeli (Fiocruz), who coordinated
the discussion about ways to combat the mosquito that transmits zika, and Paolo Zanotto (USP)
The evidences were presented by the researcher Constância Ayres, from the Department of Entomology of the Oswaldo Cruz Foundation (Fiocruz) of Pernambuco, during the 68th Annual Meeting of the Brazilian Society for the Advancement of Science (SBPC), held in early July in the Southern Bahia Federal University (UFSB), in Porto Seguro. According to Constância, some studies had shown low efficiency in the transmission of the virus by the Aedes in places like Rio de Janeiro and, when various species were analyzed, it was found that the Culex species showed an infection rate ten times greater than the Aedes aegypti's.


"If several species of Aedes are involved in the transmission environment in the field, why, in the urban environment, only one species is the vector of the virus?", asked the researcher. She reported that, until now, all studies were based on the Aedes aegypti, not considering the possibility of other vectors also transmit the virus. "After all, yellow fever, dengue and chikungunya are primarily transmitted by Aedes, then why zika would not?" Constância added that the Aedes aegypti is very rare in French Polynesia, a region that experienced zika outbreak that brought the virus to Brazil in 2013. "Some islands that had zika outbreak have no Aedes aegypti, but have a lot of Culex."

In Brazil, the stilt is the mosquito most present - around 20 times more abundant than Aedes. It was known that it transmitted arbovirus, which are genetically close to zika virus. "So why it would not also be its vector? We began to investigate and made artificial infection in the laboratory, and we are now studying the mosquito's immune response to infection." "When the mosquito feeds," said Constância, "the blood goes directly into the intestine, where there is the first barrier to infection. Then there is the escape barrier in the gut and then it must infect the salivary gland to, then, escape and go out through saliva and be finally transmitted." Therefore, there are four barriers by which the virus must pass.

So her team made the comparison between the gut and salivary gland infection and transmission rates and noted that they were very similar. They collected saliva, extracted RNA and found that the virus was indeed present. "So, in laboratory, it's the same viral load that the Aedes, the two are vectors, but the Culex is twenty times more abundant in the urban environment, so who is the greatest vector? I am convinced that is not the Aedes aegypti."

Epidemic control

The implication of having other vectors is that it drastically changes the forms of control because the two mosquitoes are different. Culex bites overnight, Aedes during the day; Aedes lays eggs in clear and stagnant water, Culex prefers extremely polluted water, requiring, therefore, investment in sanitation, which is a historical problem in Brazil. This is not, however, a goner. it is possible to map 100% of breeding in a particular area because the Culex put all its eggs in the same place, unlike the Aedes, which distributes them. "The chance of Culex control success is greater than that of Aedes. The proof is that today we can not control dengue."

Constância added that if only the Aedes were the transmitter of zika, this would be a democratic disease such as dengue, which reaches to all people, and would not be concentrated in the suburbs, reaching the poorest. She stressed that the vector control has to be done intensively, throughout the year, regardless of epidemic. "Zika is a social problem, we can not blame the mosquito."  

Minibrains and microcephaly

Stevens Rehen, research director of the D'Or Institute for Research and Education (IDOR), professor at the Federal University of Rio de Janeiro (UFRJ) and young member of Brazilian Academy of Sciences from 2008 to 2012, presented at the Annual Meeting of the SBPC his work that, using minibrains, proved the relationship between zika and microcephaly in babies born from infected mothers. The minibrains are structures developed in the laboratory using the cell reprogramming technique, that reproduce the human brain.

In 25 days of uninterrupted work, Rehen and his team observed that after infecting these structures with zika virus, there was a 40% reduction in the growth of these organoids, simulating the cerebral cortex of a fetus with a month of pregnancy, in the period 11 days. The work, developed entirely in Brazil, was published in Science magazine. "We did the same with dengue, which also infected cells, but did not affect neurogenesis," said the scientist.

Other work developed by Stevens Rehen and colleagues revealed the reduction of progenitor cells when using the isolated virus, confirming the cell death associated with this process. Another study, led by the researcher Amilcar Tanuri, showed a reduction in infection using chloroquine, which can therefore be a drug used against the virus, including to pregnant women. Both studies were shared as preprint (scientific articles that have not been published or passed through peer review, but are disclosed in the scientific community to have a quick movement).

The virus changes over time

Paolo Zanotto, professor at the Institute of Biomedical Sciences in University of São Paulo (ICB-USP), talked about the assumptions for the zika virus, which until recently did not generate major concerns, had become a severe case of health public. According to Zanotto, virus mobility was large. It was first isolated in Uganda in 1947 and moved to Malaysia around 1960. Then followed to Micronesia and until then there was no problem associated with human-to-human outbreak, but only what European called "red fever". "There was activity of the virus, but not what was observed here in the Brazilian Northeast last year."

The most important moment was 2007, when the outbreak happened in Micronesia and the virus spread throughout Central Africa, a band from South America, Mexico and Asia. Then came the congenital syndrome by zika. "One explanation for a virus that did not do anything and suddenly becomes an eyesore can be the demographic effect," Zanotto said. While French Polynesia had about 280,000 people, in Brazil, the virus found millions of susceptible individuals. "From there, you can begin to see a small sample of these thousands of cases that would be microcephaly, which did not happen in Polynesia."


(Clarice Cudischevitch for NABC)




webTexto é um sistema online da Calepino