A study by University of North Dakota researchers shows that the mosquito species Aedes vexans, which is native to North America, can transmit Zika virus. They caution, however, that the finding does not necessarily mean an outbreak of Zika in northern latitudes is close at hand or even likely. (Photo credit: Bob Peterson, Ph.D., Insects of the Greater Yellowstone Ecosystem)

By Josh Lancette

A new study from researchers at the University of North Dakota found that Aedes vexans, a mosquito species indigenous to North America, has the capability to transmit Zika. This is the first native North American mosquito species shown to be able to transmit the virus. The results are published today in the Journal of Medical Entomology.

Josh Lancette

To test the capability of the species to become infected with the virus, the researchers used mosquitoes collected from North Dakota and Minnesota and fed them blood containing Zika virus. Some (about 3 percent) developed infections. Then, infected mosquitoes were tested to see if they could transmit the virus. Surprisingly, Ae. vexans had a higher transmission rate than Aedes aegypti, which was tested alongside Ae. vexans in the study and is the primary vector of Zika.

“Because of its wide geographic distribution, often extreme abundance, and aggressive human biting activity, Ae. vexans could serve as a potential vector for Zika virus in northern latitudes where the conventional vectors, Ae. aegypti and Ae. albopictus, cannot survive,” write the researchers.

And indeed the mosquito does have a wide geographic distribution; it is often cited as the most abundant mosquito species in most of the United States as well as in Canada, France, Germany, Czech Republic, Slovakia, Hungary, Russia, Croatia, Iran, South Korea, and China.

However, while the mosquito might be capable of transmitting the virus, it doesn’t necessarily mean an outbreak of Zika in northern latitudes is close at hand or even likely.

“Just because a mosquito species is physiologically capable of transmitting a virus does not mean that that mosquito species is necessarily a dangerous vector,” says Jefferson Vaughan, Ph.D., professor of medical entomology and arthropod-transmitted diseases at University of North Dakota and one of the researchers. “There are other things at play. For instance, Zika virus is a primate virus, therefore a mosquito would have to feed twice on a human during its lifetime in order to become infected and then transmit Zika virus. Although the Ae. vexans mosquito bites people, studies indicate that it prefers to feed on larger animals such as livestock and deer. Thus, for Zika virus, the feeding behavior of Ae. vexans substantially lowers the risk of mosquito transmission from an infected to an uninfected person.”

Furthermore, the study was performed in a laboratory, which doesn’t always translate to what actually occurs in nature. To account for this factor, the researchers suggest more studies are needed.

“To help define the actual vector potential of Ae. vexans for Zika virus in North America, mosquito surveillance programs could include pools of field-collected Ae. vexans as part of their Zika virus testing, particularly in the southeast United States where Ae. vexans and Ae. aegypti co-occur and the threat of local virus amplification exists,” write the researchers. “This may reveal whether or not Ae. vexans mosquitoes are being naturally exposed to Zika virus.”

Vaughan continues the sentiment of calling for more research into the vector potential of Ae. vexans and other mosquitoes:

“This study underscores the point that when new arboviruses are introduced into the United States (such as happened with West Nile virus and Zika virus), one cannot predict in advance which mosquito species will turn out to be competent vectors for that virus,” he says. “Therefore it is vital that we maintain a cadre of trained entomologists throughout the country that are ready to conduct the necessary vector competence studies on local populations of mosquito species.”

Josh Lancette is manager of publications at the Entomological Society of America.