Health officials are making the public aware after a batch of mosquitoes tested positive for West Nile virus for the first time this year in McHenry County.
A mosquito “pool,” also known as a batch of mosquitoes, was sampled on July 13 in Fox River Grove and later tested positive for West Nile virus.
The McHenry County Department of Health said this mosquito pool is the first confirmed indicator of West Nile virus presence in McHenry County in 2021.
The health department, which conducts West Nile virus surveillance from May through October, has tested 260 mosquito batches this year and all have been negative until the latest batch in Fox River Grove.
“It is not unusual during this time and the risk of [West Nile virus] typically remains until the first hard frost,” the health department said in a statement.
According to the Illinois Department of Public Health (IDPH), there have been 81 mosquito batches positive for West Nile virus this year. The virus has not been detected in birds or humans so far in 2021.
Officials said that infected birds can become carriers of West Nile virus through the bite of an infected mosquito and then pass the virus onto mosquitoes that feed on them.
West Nile virus is transmitted to humans predominantly through the bite of Culex mosquitoes, which is the primary vector for West Nile virus transmission in Illinois.
Illness from West Nile virus is usually mild and includes fever, headache and body aches but serious illnesses, such as encephalitis, meningitis and death, are possible.
Persons 60 and older have the highest risk of serious illness. There is no vaccine available for West Nile virus.
Officials say the best way to prevent West Nile virus is to reduce the number of mosquito breeding sites around homes and to take personal precautions.
It is recommended to empty standing water from containers around the house like tires, neglected swimming pools, birdbaths, clogged gutters and buckets.
It is also recommended to make sure doors and windows have tight-fitting screens and use insect repellents containing 20% or more of DEET.