West Nile virus has been found in three different mosquito pools in Boone County, according to the Missouri Department of Health and Senior Services. The mosquito-borne disease has yet to appear in birds or humans in the area. One human case of West Nile has been confirmed in St. Charles.
Boone County is one of three Missouri counties with West Nile-positive mosquitoes, according to the national Centers for Disease Control and Prevention. As of Tuesday, St. Louis County had 72 infected pools and St. Charles County had two.
Nationwide, 265 human cases of West Nile have been reported — 161 in Arizona alone. Six have died.
West Nile arrived in Missouri in late May, two weeks earlier than last year and a month earlier than two years ago. A crow was found May 24 in Osceola in west-central Missouri. The following day, a grackle was found in the St. Louis suburb of O’Fallon. Tests at MU’s Veterinary Diagnostic Laboratory confirmed on June 2 that both were infected with West Nile, said Howard Pue, state public health veterinarian.
In 2002, the first known year for West Nile to strike humans, 168 people were infected and seven died. Last year, 64 were infected and eight died.
Dr. Gayle Johnson of the Veterinary Diagnostic Laboratory said it is difficult to tell what caused the drop-off in infections, but part of it can be attributed to increased public awareness.
Because approximately 80 percent of people who are infected will not show any symptoms, Johnson and Pue said it is likely greater numbers of people are infected with the disease than are reported.
Up to 20 percent of people infected will show mild symptoms including fever, headache, nausea, vomiting and sometimes swollen lymph glands or a skin rash, according to the CDC.
About one in 150 people infected with West Nile will develop severe illness. People over the age of 50 are more likely to develop serious symptoms.
Pue said the state health department is working with agencies across the state to contain the virus by keeping tabs on the mosquito population, testing live and dead birds and looking for West Nile in horses and humans.
“It’s a two-fold punch involving surveillance and getting the word out,” Pue said.
Gerry Worley, environmental health manager for the Columbia/Boone County Health Department, said his department is working in concert with the state to control the mosquito population and get information to the public.
Worley said the main component of mosquito population control is using larvacide in areas of stagnant water. Larvacide targets mosquitoes before they can fly. He said spraying for adult mosquitoes is usually a last resort because of the cost.