Infection
Mosquitoes test positive for West Nile, Jamestown Canyon viruses in Washtenaw Co.
The Washtenaw County Health Department is reminding residents to prevent mosquito bites after testing found the insects can carry two types of viruses.
Mosquitoes collected in the county last week tested positive for Jamestown Canyon virus and West Nile virus, the county health department said in a news release.
A total of four samples tested positive: three for Jamestown Canyon virus and one for West Nile virus. The collection sites are spread across the county in Ann Arbor, Independence Lake County Park in Whitmore Lake, Pinckney Recreation Area and Ypsilanti. No human cases of either virus have been reported.
The best way to prevent infection is to avoid mosquito bites, said Dr. Juan Luis Marquez, the Washtenaw County Health Department medical director.
“Unfortunately, mosquitoes can spread disease,” Marquez said. “These results confirm the potential for human infections in our local area, and we should all take steps to prevent getting mosquito bites.”
Most people infected with either of Jamestown Canyon or West Nile do not become ill or experience only mild illness. In rare cases, infections can become serious. The health department does not recommend avoiding the outdoors but urges using preventative measures. Use appropriate repellant, wear protective clothing and avoid areas with mosquito activity whenever possible.
“Our mosquito surveillance can help with early detection of infections,” said Kristen Schweighoefer, environmental health director with the county’s Heath Department. “We’ll continue to monitor throughout the summer while mosquitoes are active.”
Jamestown Canyon Virus (JCV)
In 2021, six human cases of JCV were reported in Michigan and one in 2022. No cases were in Washtenaw County residents.
Most cases occur from late spring through mid-fall. Illness can develop within a few days to two weeks following a bite from an infected mosquito, the health department said in the release. While most people do not become ill, initial symptoms can include fever, headache, and fatigue. In rare cases, it can cause severe disease in the brain and/or spinal cord including encephalitis and meningitis.
While the JCV is found throughout much of the U.S., cases have been increasing in the Midwest. According to the Michigan Department of Health and Human Services, this likely reflects increased awareness and testing but may also be due to an increase in the presence of the virus in the environment. This is the third year that the MDHHS has offered virus testing of mosquito pools collected by local health departments and county mosquito control programs.
West Nile Virus (WNV)
In Michigan last year, 12 human cases of WNV were reported. Washtenaw County has not had a human case of WNV reported since 2018.
Most people infected with West Nile virus have no symptoms of illness, but some may become ill three to 15 days after the bite from an infected mosquito. About 1 in 4 people infected will experience mild illness with a fever, and headache and body aches, sometimes with a skin rash and swollen lymph glands.
Less than 1% of people who get bitten and become infected with West Nile virus will develop a severe illness like encephalitis or meningitis, the health department said. The risk of getting West Nile encephalitis is higher in people 50 years of age or older. More severe infections include convulsions, disorientation, headache, high fever, muscle weakness, stiff neck or paralysis. In a few cases, mostly among the elderly, it can be deadly.
Prevention
- Apply insect repellent that contains the active ingredient DEET or other EPA-approved products to exposed skin or clothing. Follow directions for use.
- Wear light-colored, long-sleeved shirts and long pants when outdoors. Apply insect repellent to clothing to help prevent bites.
- Maintain window and door screening to help keep mosquitoes outside.
- Empty water from mosquito breeding sites around the home, such as buckets, kiddie pools and other water-holding containers where mosquitoes can lay eggs.
