Virginia sees surge in West Nile virus

A female Culex quinquefasciatus mosquito on the skin of a human host. The mosquito's red-colored abdomen is filling with blood. C. quinquefasciatus is among the mosquitoes responsible for spreading the arboviral encephalitis, West Nile virus. (James Gathany/ Centers for Disease Control and Prevention)

So far this year there have been 38 cases of West Nile virus in Virginia, a new record for the state.

On average, Virginia reports only about nine cases per year, according to the Department of Health.

The cases have been spotted in 17 health districts across the state, with Fairfax seeing the most at 7 cases and Central Shenandoah one step behind with six cases. The rest of the districts have reported between one and three cases each.

“These cases serve as a reminder that mosquitoes that transmit WNV can be active as late as the end of October here in Virginia, and so we are advising the public to avoid mosquito bites until the first frost,” said State Health Commissioner Dr. Norman Oliver in a Department of Health news release.

The trend continues the significant uptick in sicknesses caused by mosquitoes, ticks and fleas that the Centers for Disease Control and Prevention reported earlier this year. Diseases transmitted by those insects tripled between 2004 and 2016.

One of the most basic explanations for the surge in West Nile could be rising summer temperatures. Mosquitoes love heat and are able to easily transmit the virus when exposed to consistently warmer temperatures.

The research group Climate Central released a report in early August stating that so-called mosquito disease danger days — when the average temperature is between 61 and 93 degrees — are rising.

Mosquito activity can be a bit more complicated than simply temperature, though. Rain, for instance, often washes away the homes of some of the most common West Nile-carrying mosquitoes, according to David Gaines, Virginia’s public health entomologist.

But warm springs, like the one Virginia had this year, can also give a boost to West Nile virus transmission, Gaines said.