Killing every mosquito in town might not guarantee stopping the Zika virus.
Researchers say it appears female Aedes aegypti mosquitoes can pass along Zika to their eggs and offspring.
They published their findings today in the American Journal of Tropical Medicine and Hygiene.
The research could alter the way health officials attempt to control the spread of the virus as well as raise concerns over a reemergence of Zika in areas where a cold winter may eliminate a population of adult mosquitoes.
"The implications for viral control are clear," said study co-author Dr. Robert Tesh, a professor at the University of Texas Medical Branch, in a press release. "It makes control harder. Spraying affects adults, but it does not usually kill the immature forms — the eggs and larvae. Spraying will reduce transmission, but it may not eliminate the virus."
Low ratio, high incidence
In their study, the researchers injected laboratory-raised mosquitoes with the Zika virus.
The following week, the mosquitoes laid eggs. The scientists collected and incubated those eggs.
After the infant mosquitoes hatched, and then reached adulthood, researchers discovered traces of the Zika virus in one out of every 290 mosquitoes.
"The ratio may sound low," Tesh said, "but when you consider the number of [mosquitoes] in a tropical urban community, it is likely high enough to allow some virus to persist, even when infected adult mosquitoes are killed."
The same species of mosquito is known to spread dengue and yellow fever to their offspring. Other types of mosquitoes spread diseases such as West Nile and St. Louis encephalitis to their eggs.
Dr. Lee Norman, the chief medical officer at the University of Kansas Hospital, agreed that the low ratio doesn’t necessarily mean the Zika virus wouldn’t emerge strongly in a second generation of mosquitoes.
“It casts things in a little different light,” he told Healthline. “The fact it can happen biologically is worrisome enough.”
Implications of the discovery
Scientists say this latest discovery has several implications on efforts to control the spread of the Zika virus.
The first is the spraying of neighborhoods to kill adult mosquitoes. Eradication may now have to be extended to finding the mosquitoes’ nests of eggs.
The second is on the emergence of a new generation of mosquitoes.
Mosquitoes only live a few months, so in tropical areas a cold winter can rid an area of almost all of its adult mosquitoes.
This “wintering over” effect was considered to be helpful in controlling the Zika virus.
However, Norman said the prospect of new mosquitoes with the virus hatching in the spring changes that.
“It brings up the possibility of always having an availability of Zika the next year,” he said.
Norman said that even with a small number of infected young mosquitoes, there can be a “tipping point” where they transmit the disease to enough humans to spread the disease further in the mosquito population and then cause an outbreak
He added the discovery highlights the need for more funding for Zika research.
He said the pattern with most diseases is money, and focus doesn’t happen until a virus infects a substantial number of humans. That was the case with Ebola.
Norman hopes Congress will soon approve more funding for Zika research, including the search for a vaccine.
“It’s been frustrating to the medical and scientific communities,” Norman said. “We need to accelerate the research on Zika.”
Blood testing recommended
The spread of Zika in Puerto Rico, Florida, and other communities in the United States prompted action Friday from the Food and Drug Administration (FDA).
FDA officials announced they are recommending testing for the Zika virus in all donated blood and blood components in the United States.
The Zika virus causes mild flu-like symptoms in most people who are infected, according to the Centers for Disease Control and Prevention (CDC).
However, pregnant women who become infected can pass along serious brain diseases such as microcephaly to their unborn children.
The CDC reports there are nearly 1,400 cases of pregnant women with lab evidence of Zika infection in the United States and its territories.
In all, more than 11,000 Zika cases have been reported in the U.S. and its territories.