Mosquito Species in California Could Transmit Zika Virus, Study Finds

July 12, 2018

A species of mosquito that has infected people with the Zika virus in at least two states has also been detected in California, according to a recently published study.

According to the study, published in June 2018 in the journal PLoS Neglected Tropical Diseases, researchers at the University of California in Davis infected three species of mosquitoes — Californian Aedes aegypti, Culex tarsalis, and Culex quinquefasciatus — with Zika strains from 2015 outbreaks in Puerto Rico and Brazil, and a 1966 outbreak in Malaysia.

The mosquitoes developed Zika by biting an infected mouse, and the researchers then tracked each mosquito to see if it could transmit the virus.

While no virus was found in the two Culex species, 80 to 90 percent of the Aedes mosquitos had Zika RNA, or genetic material, in their saliva.

Lark Coffey, PhD, an assistant professor in the departments of pathology, microbiology, and immunology at the School of Veterinary Medicine at UC Davis, and the co-lead researcher on the study, says the team had the data on the mosquitoes a year ago and alerted the California Department of Public Health.

“It wasn’t surprising; after all, these mosquitoes capable of transmitting Zika have been found in Texas and Florida,” says Dr. Coffey. She adds that all states need to be vigilant.

“We have to continue aggressive surveillance of both the environment and humans, so we can act quickly in case of an outbreak,” says Charles Bailey, MD, an infectious disease specialist with St. Joseph Hospital in Orange, California.

"Understanding the mosquito species that can transmit Zika is important for estimating regional outbreak potential and for informing local mosquito control strategies, such as spraying communities at risk with insecticide,” says Coffey.

About the Zika Virus

The effects of the Zika virus range from mild flu-like symptoms to serious neurologic conditions in adults and birth defects in babies. It is most commonly spread when people are bitten by a mosquito carrying the virus. The two known species that can spread the virus are Aedes aegypti and Aedes albopictus.

The disease can also be spread through sexual contact with a person who has the virus.

Most cases of Zika diagnosed in the United States have been brought in by travelers who contracted the virus in other countries, generally South and Central America.

U.S. Cases in Recent Years

According to the Centers for Disease Control and Prevention (CDC), there were 5,168 Zika cases reported in the United States in 2016. Nearly 4,900 cases were in travelers returning from affected areas, 224 cases were presumed to be from local transmission by mosquito, and 47 cases were acquired through sexual contact, contact in a research lab, or other unknown person-to-person contact.

In 2017, the number of U.S. cases dropped to 452, of which 437 were travelers returning from affected areas, seven were from local mosquitoes in Florida and Texas, and eight were through sexual or laboratory transmission.

“The number of recent cases has dropped dramatically, though that absolutely doesn’t mean an outbreak can’t occur again,” says Coffey. So far in 2018, only 28 cases have been reported in the United States, all in travelers who contracted the virus in other countries.

Preventing Mosquito Bites Is Key

Dr. Bailey agrees that the drop in the number of cases shouldn’t stop people from being vigilant about preventing mosquito bites.

“It’s not just Zika. Mosquitoes can spread other serious illnesses,” says Bailey. Other mosquito-borne diseases include West Nile virus, Chikungunya virus, and dengue.

To help avoid mosquito bites, the CDC recommends:

“A study like this reminds government officials and private foundations of the need to continue funding research to help find vaccines and treatments as well as allocate funds for people who become disabled by the virus,” Bailey says.

Several vaccines to prevent the Zika virus are currently in clinical trials, though a vaccine for wide use is at least a couple of years away, he adds.

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