Pools of mosquitoes along the boundary of Richmond and Henrico County have tested positive for the West Nile virus, and health officials are warning residents throughout the region that they need to protect themselves.

Though the mosquitoes were found along the northern and western boundary between the county and city, “the general thinking is, if we test mosquitoes and they’re positive in those sites, the likelihood is we’ll have positive mosquitoes all over the region,” said Dr. Danny Avula, director of the Richmond City Health District.

West Nile isn’t new to the Richmond region or to Virginia in general. Last year, the state saw eight cases, and so far this year there has been one. Avula said there have not been any cases in the Richmond region so far this year.

He said the health department views the detection of the virus in local mosquitoes as a red flag.

“It says, ‘Hey, West Nile is here,’” he said. “It’s been a few years since we had our last serious documented case here in Richmond, but it’s something people need to be aware of.”

Between 2010 and 2016, there were zero to two cases of West Nile in the Richmond area annually.

“The good news is most people who get it have a pretty mild course,” Avula said. “You get a fever and a little headache and achiness.”

The Centers for Disease Control and Prevention’s website states that 8 out of 10 people infected with West Nile will not show symptoms. Most who do recover quickly, but weakness can persist for weeks or months. Fewer than 1 percent who are infected develop neurological illnesses like encephalitis or meningitis.

Fatalities can happen, but they are rare, said Melissa Viray, deputy director of the Richmond City Health District. She said only about 10 percent of those who develop serious illness die, and typically those are people whose immune systems are compromised by another health issue.

“That risk subset is really people who are over the age of 60 and typically have other underlying conditions like diabetes or kidney disease,” Avula said.

There is no specific treatment for West Nile, and symptoms typically appear two to 15 days after exposure.

Avula said the city and health district already have programs in place for mosquito control, many of which are being carried over from work last year to prevent local transmissions of the Zika virus.

Also a mosquitoborne virus, Zika is found largely in the Caribbean and Latin America. It causes only mild, flulike symptoms, but can be dangerous for pregnant women because it can cause birth defects. There have been local transmissions of the virus in Florida and Texas.

Since April, the Department of Public Utilities has been treating various locations throughout the city with larvicide to prevent mosquitoes from breeding.

“We just came off the year with Zika, where we went hard and heavy with mosquito messaging,” Avula said. “All the same things pertain here: Even though it’s a different species of mosquito, they breed in similar habitats — shallow water that builds in tires or flower pots or children’s toys.

“So we need to do the same thing — to eliminate those mosquito breeding habits, wear protective clothing and wear insect repellent.”

Zika is largely spread by Asian tiger mosquitoes, which bite throughout the day. West Nile is primarily carried by Culex mosquitoes, which usually bite from dusk to dawn — though they can still bite anytime, so Avula recommended residents use prevention techniques throughout the day.

In a public health notice, the health district encouraged city residents to eliminate stagnant water where mosquitoes might breed.

Additional protections include wearing insect repellent that contains DEET or another EPA-registered active ingredient, wearing light-colored long sleeves and pants, or staying indoors during those times.

Turning over objects that collect rainwater to eliminate areas where mosquitoes can breed is also a good way to lower possible exposure to mosquitoes, as is equipping open windows and doors with screens to keep them out of the home.

Dr. Gonzalo Bearman, chairman of the division of infectious diseases at VCU Health, called these tactics “common-sense interventions” that he encouraged everyone in the Richmond region to employ.

“There is no epidemic of West Nile Virus in Virginia right now, so the likelihood of getting infected with West Nile virus is low,” he said. “But that doesn’t mean the risk is not real.”

koconnor@timesdispatch.com

(804) 649-6813

Twitter: @katiedemeria

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