TEXAS, United States, Friday September 9, 2016 – The latest bad news in the litany of Zika woes reveals that scientists have found that mosquitoes can pass the virus to their young in their eggs, meaning that the juveniles will be born carriers of the disease, making control of its spread even harder.
This new obstacle in the fight against Zika is nevertheless no surprise. Mosquitoes can infect their larvae with other viruses, too, including dengue.
“It makes control harder,” said Dr Robert Tesh of the University of Texas Medical Branch in Galveston.
“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.”
Under normal circumstances, it takes mosquitoes and people to spread a virus. The bugs bite infected people, incubate the virus, and then bite other people and spread it.
With vertical transmission – mosquitoes hatching with the virus primed to go – the virus spreads even if all the adult mosquitoes in an area have been wiped out.
For their research, Dr Tesh and colleagues infected Aedes aegypti and Aedes albopictus mosquitoes with Zika and then tested the eggs they laid.
The infected Aedes aegypti mosquitoes did pass the virus to their eggs, the researchers reported in the American Journal of Tropical Medicine and Hygiene.
The good news was that the transmission wasn’t most or even much of the time. It occurred about one in every 290 times.
Tesh reasoned that meant it was probably not a major way Zika stuck around.
“I think it just another survival mechanism for the virus to make it through the season,” he said.
More good news came with the finding that Aedes albopictus, the so-called Asian tiger mosquito that can carry Zika and has a much broader range than Aedes aegypti, did not transmit Zika to its eggs.
The World Health Organization (WHO) and the US Centers for Disease Control and Prevention (CDC) still maintain that the best way to fight Zika is to fight the Aedes mosquitoes that carry it.
But that’s easier said than done, with the mosquitoes laying their eggs in even the smallest containers and needing only a few drops of water to hatch.
According to Tesh and other experts, spraying insecticides to kill adult mosquitoes cannot wipe out Aedes, since the eggs are impervious to insecticides or other chemicals.
The eggs are very resilient, can survive being dried out, and stick well to the site where they were laid, moreover, so simply emptying containers regularly does not necessarily get rid of the mosquitoes.
“You have to scrub the inside of the container. That is the way to get rid of the eggs,” Tesh said.
Zika has spread relentlessly across Latin America and the Caribbean over the past year and has caused outbreaks in Florida with more expected.
It can cause grievous birth defects if contracted by a pregnant woman, and can cause the paralyzing condition Guillain-Barré syndrome in adults.
There’s no drug to treat it and no vaccine to prevent it.