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8/2/23 correction: Washtenaw County had one human case of Jamestown Canyon virus in 2022. This resident was likely exposed in Washtenaw County.
Spanish translation: ¡Lucha contra las picaduras! Prevenga las enfermedades transmitidas por mosquitos Detectados los virus Cañón de Jamestown y West Nile en mosquitos locales
July 21, 2023 – Washtenaw County Health Department reminds local residents to prevent mosquito bites. Mosquitoes collected in Washtenaw County last week have tested positive for Jamestown Canyon virus and West Nile virus. A total of four samples tested positive: three for Jamestown Canyon virus and one for West Nile virus. These collection sites are spread across the county (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.
“Unfortunately, mosquitoes can spread disease,” says Juan Luis Marquez, MD, MPH, medical director with Washtenaw County Health Department. “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 precautions. Use appropriate repellant, wear protective clothing, and avoid areas with mosquito activity, whenever possible.
“Our mosquito surveillance can help with early detection of infections,” says Kristen Schweighoefer, MPH, RS, environmental health director with the Washtenaw County Health 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. None of these were in Washtenaw County residents.
The JCV virus is spread to people through bites from infected mosquitoes. 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. 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 (MDHHS), 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. This testing program identified the positive results in Washtenaw.
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 3 to 15 days after the bite from an infected mosquito. About 1 in 4 people infected will experience mild illness with fever, 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 risk of getting West Nile encephalitis is higher in persons 50 years of age or older. More severe infection may be marked by convulsions, disorientation, headache, high fever, muscle weakness, stiff neck, or paralysis. In a few cases, mostly among the elderly, death may occur.
Avoiding mosquito bites is the best way to prevent mosquito-borne diseases.