The number of animals testing positive for West Nile virus has spiked over the past week. Gayle Johnson, MU associate professor of veterinary pathobiology, said that even though the mosquito season is waning, West Nile still poses a risk for both animals and humans.
“Mosquitoes are still out there and some are infected,” said Johnson, who works at MU’s Veterinary Medical Laboratory, where animals from across the state are tested for the virus.
The number of horses testing positive at the laboratory has jumped from 50 percent to
75 percent over the past week, Johnson said.
Mosquitoes carrying the virus were found in rural areas, Johnson said. No infected mosquitoes were found among those trapped by the lab in suburban Columbia, however.
As of Monday, three horses had tested positive in Boone County. About this time last year, there were eight, Johnson said. The decrease this year is because many horses were vaccinated after last year’s scare. Statewide, 78 horses have tested positive, compared with 208 last year. About a third of infected horses die.
No cases of human West Nile infections were reported this year in Boone County. In 2002, one person was infected. The Missouri Department of Health reported 15 cases in the state as of Monday.
Last year, Missouri had 168 cases overall. Nationally so far this year, 3,659 cases have been reported, and 67 people have died, a Tuesday report from the Centers for Disease Control and Prevention shows.
West Nile virus symptoms include slight fever, headache, body aches, skin rash and swollen lymph nodes. More severe infections can include inflammation of the brain or meningitis. Infected horses have trouble walking or show other signs of brain disease, Johnson said.
Birds are also affected by the virus. The number of dead birds testing positive is close to 100 percent, Johnson said. She said birds come from public health departments across the state and tests are done on highly susceptible species such as crows and blue jays.
Last year, West Nile infections in Missouri peaked in early October. Johnson said people should be vigilant, because there is no magic chart that can predict the degree of viral infection in mosquitoes over the next two months. The main times mosquitoes bite are dusk and dawn. Also, the risk is higher if people have standing water close to their homes.
Johnson — who said she has been teaching herself to think like a mosquito — said they don’t mind the coming of fall. “They are still happy to bite in cold weather,” she said.