GREENFIELD — Local mosquitoes have tested positive for West Nile virus.
Data from the Indiana State Department of Health show Hancock County has joined nearly 20 other Indiana counties in having batches of mosquitoes carrying the disease.
The virus is transmitted to humans through bites and can cause flu-like symptoms. Most people will show no symptoms if they become infected, but the illness is especially dangerous to young children and senior citizens, and health experts said local residents should take precautions.
In central Indiana, Shelby, Hamilton, Marion and Morgan counties all have mosquitoes that have tested positive.
The same data show no human cases have been confirmed in the Hoosier state so far, but Bryan Price, senior vector-borne epidemiologist for the state health department, said officials said it’s only a matter of time before people are infected.
The presence of the virus in mosquitoes is not unusual. It was first found in the United States more than 15 years ago and has been in Hancock County for more than 10 years.
The virus exists in a cycle between birds and mosquitoes, Price said. Every spring, that cycle begins again and is found in people around the end of July and beginning of August, he said.
“West Nile virus has been in Indiana since 2002, and it’s not going anywhere. We’re stuck with it,” he said.
About 75 percent of people who are infected with West Nile show no symptoms, according the federal Centers for Disease Control and Prevention. About one in five people will develop symptoms, and most recover completely, though fatigue and weakness might last for weeks.
Fewer than 1 percent of people who are infected will develop encephalitis or meningitis — swelling of the brain or its surrounding tissues.
In humans, symptoms generally appear between three and 15 days after a bite. They include high fever, severe headache, neck stiffness, muscle weakness, paralysis, nausea, vomiting, sore joints and confusion.
Anyone living in an area where West Nile virus is present in mosquitoes can become ill from the disease, according to the CDC. Those who spend a lot of time outdoors are more susceptible because of greater exposure to mosquitoes.
In Hancock County, at least two batches of mosquitoes tested had positive results. Marion County has had at least seven batches test positive, and Hamilton County has had six, while Shelby County has had three.
There is no vaccine to prevent the disease, and there are no medications to treat it.
Greenfield Street Commissioner Tyler Rankins said city crews have fogged the entire city once in an effort to prevent mosquitoes. Crews are about halfway through a second go-round.
Mosquitoes breed in pools of water. Unfortunately, the summer has been extremely rainy — the greater Indianapolis area has received nearly 22 inches of rain since June 1, Rankins said.
“The mosquitoes have been so bad, we can’t really get a handle on them,” he said.
There’s no way to prevent the spread of the virus among the mosquito population, Price said.
Fogging helps, but there’s no way to kill every mosquito, he said.
Residents can protect themselves and their families from the disease by avoiding the outdoors around dawn and dusk when mosquitoes are most active, Price said.
Removing standing water from properties will help residents protect their families. Small pools, ponds, dog dishes and birdbaths with standing water create the perfect breeding ground for mosquitoes, he said.
Using insect repellant with DEET also is helpful in preventing bites.
A person experiencing symptoms consistent with West Nile virus should visit a doctor for further care, according to the CDC.