Warning signs for West Nile virus are starting to flash on the West Coast, experts say.

West Nile virus is the most common cause of mosquito-borne disease in the continental US, with thousands of cases reported to the US Centers for Disease Control and Prevention every year, said Dr. Erin Staples, the medical epidemiologist in charge of the agency’s arboviral diseases branch.

The virus doesn’t cause symptoms in about 80% of people who contract it, but 1 in 5 can have fever with muscle aches, headache and rash, Staples said. A smaller proportion of people – about 1%, according to Dr. Vicki Kramer, chief of the California Department of Public Health’s Vector-Borne Disease Section – develop severe disease, an infection involving the central nervous system that can cause paralysis or death.

“Some individuals that recover have ongoing neurologic symptoms for years, so it can be very serious,” Kramer said. Older people and those with medical conditions like diabetes, high blood pressure or a weakened immune system are most at risk. There are no vaccines or treatments for the virus in people.

West Nile, named for the region in Uganda where it was identified in 1937, is typically spread in the US by a mosquito called Culex, found across the country, Staples said.

The mosquitoes, which can also transmit St. Louis encephalitis virus, “tend to like the dusk and dawn period,” she said, unlike the kinds of mosquitoes that transmit diseases like dengue, the Aedes aegypti and Aedes albopictus, which are more active during the day.

West Nile spreads as mosquitoes bite infected birds and then people, making both bird and mosquito populations important parts of public health surveillance for the disease.

ACCORDING TO CNN— “ A historically wet winter and, now, hotter summer are leading to “pretty big” warning signs for West Nile virus in the Western US, public health and mosquito control experts say, suggesting that residents should take care to avoid bites.

“The number of mosquitoes that have hatched off after the spring snowmelt is pretty tremendous in many of the states, whether it be Colorado or Utah or California,” said Daniel Markowski, technical adviser for the American Mosquito Control Association.Many districts are starting to see West Nile virus in mosquitoes, he said, meaning “you’re at the right temperature, the right mosquito population and the right time of year for localized outbreaks to occur.”

Copyright/News source: CNN

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