Missourians should take steps to reduce their exposure to West Nile virus, which first appeared in the state last fall and is expected to return later this year, University of Missouri extension and state specialists said.
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The most effective control for West Nile virus is to eliminate mosquitoes’ breeding sites around the home, urban entomology specialist Richard Houseman said. “These sites include any standing water: lower pots, tin cans, dog bowls, clogged rain gutters, old tires.”
Houseman said the virus, which is transmitted by mosquitoes and affects birds, humans and horses, was reported as early as February in Florida. “We don’t expect to see cases in Missouri until later this year, but this is a good reminder to be prepared.”
The virus was first reported in the United States in 1999 and has spread farther west each year, said Chuck Massengill, veterinary epidemiologist with the Missouri Department of Agriculture. “It might go clear to the Rockies by the time this summer is over.”
West Nile was detected last year near St. Louis in eight crows, which along with blue jays and raptors are among the most susceptible bird species. No cases involving humans or horses were reported in Missouri.
This year, horse owners can protect their animals with a West Nile virus vaccine that is now generally available, Houseman said. “The vaccine is a two-dose series, and they should get both doses.”
The federal Centers for Disease Control said West Nile virus has been fatal to about 40 percent of the horses found to be infected. The virus multiplies in the horse’s blood system and infects the brain, interfering with the central nervous system and leading to West Nile encephalitis, or inflammation of the brain tissue, resulting in coma and death.
The vaccine is expensive, Massengill said. “The company that makes it is not able to keep up with the demand, so they’re trying to funnel the supply into areas that have had the greatest exposure.”
Robert Pierce, MU extension fish and wildlife specialist, said the mild Missouri winter this year could contribute to a more rapid spread of the virus. “We’ve had active mosquitoes earlier this year,” he said. “The virus might show up sooner this year because of the early spring.”
West Nile Virus has been reported in more than 100 bird species so far, Pierce said. “Birds are the species that contribute to the spread of the virus. They’re mobile: If a bird in Missouri is infected and flies to Kansas, and then a mosquito picks up a blood meal from that bird – it’s just that quick.”
“Likewise, infected mosquitoes can hitch a ride in vehicles and travel a long distance, said Alex Bermudez, MU associate professor of veterinary pathology.
He said that while almost all bird species might eventually be found to be somewhat susceptible, “my guess is that a lot of them will have an inapparent infection. They’ll get the virus, develop an immunity and never look back.”
What should people do if they find a dead crow, jay or raptor on their property? “From a public health stand standpoint, my recommendation is for them to report it to the Missouri Department of Health or their local public health officials,” Bermudez said. “The departments of public health are monitoring the problem across the state.”