Officials at the Missouri Department of Health and Senior Services report no West Nile virus so far this spring.
This is the time of year when mosquitoes breed in the Show-Me state.
Last year, West Nile virus soared nationwide, with more than 1,100 cases reported.
The elderly and children are at the highest risk of the disease carried by mosquitoes.
The insects breed in standing water.
Boone County Environmental Public Health Supervisor Kala Wekenborg said, "Any mosquito larvae that could have been placed in those pools would be flushed out because we are receiving more rain on a pretty frequent basis. As the drier parts of the summer come upon us, the risk for West Nile would become more heightened because water would standing."
About 80% of people infected with West Nile virus won't show any symptoms, but 20% may develop a fever, headache, body ache, vomiting, swollen lymph glands or a skin rash.
Health officials said bug repellent containing the chemical DEET is the best way to prevent West Nile virus.