Mosquitoes carrying Zika can hand down virus to offspring, study shows

Like a physical trait or a family heirloom, the Zika virus can be handed down by an infected female mosquito to some of her offspring, a new study shows.

The study, by scientists at the University of Texas Medical Branch in Galveston, confirms that so-called vertical transmission of the virus occurs in Aedes aegypti mosquitoes, the main species responsible for the spread of Zika.

But vertical transmission doesn’t always happen. In fact, the research suggests it only occurs at a rate of 1 in every 300 mosquitoes.

Still, given that mosquito populations are massive, that rate of transmission probably is frequent enough to allow the virus to persist in places where a period of adverse weather conditions — a stretch of dry or cold weather — kills off adult mosquitoes, said Dr. Robert Tesh, director of the World Reference Center for Emerging Viruses and Arboviruses, housed at the university.

“I don’t think it’s going to change the epidemiology of the disease,” said Tesh, who is the senior author of the paper, published in the American Journal of Tropical Medicine and Hygiene. “The only thing it means is that it’s possible that the virus could survive [in a location] say from one season to the next.”

Joseph Conlon, a retired Navy entomologist who is now technical adviser for the American Mosquito Control Association, agreed with Tesh’s read of the situation.

Conlon said in the United States, Zika’s spread is more likely to be driven by people returning home from Zika-affected cities and towns than by vertical transmission in mosquitoes.

“We’re going to have continual reintroduction of this virus in people. They’re the main problem. People coming in,” he said.

Many viruses related to Zika and spread by Aedes mosquitoes are transmitted from mother to offspring in this way.

To test whether the same kind of transmission occurred with Zika, Tesh’s team injected the virus into the gut of female mosquitoes. After the mosquitoes mated and laid their eggs, the eggs were hatched and tested for the presence of the virus.

The group studied both Aedes aegypti mosquitoes — in which vertical transmission was seen at a rate of one per 290 offspring — and Aedes albopictus mosquitoes. It’s not clear if the latter species plays a role in the transmission of Zika in a real world setting, though they can be infected with the virus in a lab.

Tesh’s team did not see vertical transmission with albopictus mosquitoes, but tested fewer of them. He suggested, based on the numbers, scientists cannot rule out that vertical transmission could happen in that species.

Conlon said the fact that vertical transmission occurs adds another layer of complexity to controlling these already hard-to-control mosquitoes.

He suggested a multipronged approach is needed, one that is grounded in changing the public’s attitudes toward mosquitoes.

“The fact is when we allow trash to accumulate and water to get into the trash to grow these Aedes aegypti mosquitoes, we’re part of the problem,” he said.

“We have to make it socially unacceptable, kind of like we did with smoking.”