WASHTENAW COUNTY, Mich. – Mosquitoes collected in Washtenaw County last week tested positive for two viruses.
Three samples tested positive for Jamestown Canyon Virus and one tested positive for West Nile Virus. There have been no human cases of either virus reported.
The collection sites are spread across Washtenaw County and include Ann Arbor, Independence Lake County Park in Whitmore Lake, Pinckney Recreation Area, and Ypsilanti.
“Unfortunately, mosquitoes can spread disease,” said 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 virus do not become ill. If they do become ill, they usually only experience mild symptoms. In rare cases, infections can become serious.
The health department is asking residents to use appropriate bug repellant, wear protective clothing and avoid areas with mosquito activity when possible.
Jamestown Canyon Virus (JVC)
There were 10 cases of JVC in Michigan between 2012 and 2021 that were reported to the CDC.
JCV sickened three Michigan residents in 2020. Most cases occur from late spring through mid-Fall. Illnesses can develop within a few days to two weeks after a bite from an infected mosquito. Most people do not become ill.
Symptoms include fever, headache and fatigue. In rare cases, JVC can cause severe disease in the brain and/or spinal cord including encephalitis and meningitis.
According to Michigan, there were 12 JVC-positive mosquito pools in 2022 and one human JCV case.
West Nile virus (WNV)
Most people who become infected with WNV do not develop any symptoms. When people do become ill symptoms include headache, body aches, joint pains, vomiting, diarrhea or rash. Most people with that type of WNV recover completely.
About 1 out of 150 people infected will develop a serious neurologic illness. Symptoms include, headache, high fever, neck stiffness, disorientation, coma, tremors, seizures or paralysis.
According to Michigan officials, there were 77 WNV-positive mosquito pools in 2022 and there were 12 human WNV cases.
Preventing mosquito bites
Michigan officials suggest taking the following steps to prevent mosquito bites:
- When used as directed, Environmental Protection Agency (EPA)-registered insect repellents with one of the active ingredients below are proven safe and effective, even for pregnant and breastfeeding women: DEET, Picaridin (known as KBR 3023 and icaridin outside the US), IR3535, Oil of lemon eucalyptus (OLE), Para-menthane-diol (PMD), and 2-undecanone.
- 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, unused kiddie pools, old tires or similar sites where mosquitoes lay eggs.
- You could also hire a mosquito control business. Mosquito control businesses are required to be licensed to apply pesticides in Michigan. A list of Michigan firms licensed to apply pesticides is available online.
Mosquitoes lay eggs in or near standing water
Mosquitoes need standing water to reproduce. That’s why you should empty, scrub or cover any items that hold water.
Standing water is often found in old tires, buckets, planters, toys, pools, birdbaths, flower pot saucers or trash containers.
Mosquitoes can complete their life cycle in about a week. The CDC recommends using an outdoor insect spray made to kill adult mosquitoes. Mosquitoes are often found in dark, humid areas.
Can’t remove standing water? Larvicides are an option
If you’re unable to remove the standing water where you live then you’ve got one other option: Larvicides.
Larvicides work by killing mosquito larvae and pupae before they grow into pesky adults. According to the CDC, if you use larvicides correctly they do not harm people, pets or the environment.
Larvicides come in liquids, tablets, bits, pellets, granules and briquettes. You use them by applying them where mosquitoes lay eggs (that means anywhere that holds standing water). That can include buckets and rain barrels, fountains, gutters or downspouts, non-chlorinated swimming pools, pool covers that collect water, tires and tree holes.
Use larvicides to treat standing water that will not be used for drinking and cannot be covered, dumped or removed.