Mosquitoes Test Positive for Eastern Equine and West Nile Virus

The New York State Department of Health has informed Suffolk County health officials that two more mosquito samples have tested positive for the Eastern equine encephalitis virus. The samples, both Culiseta melanura, were collected on Aug. 22 from Manorville.

A mosquito sample collected in Manorville on Aug. 16 also tested positive for the virus.

On Aug. 25, Dr. James Tomarken, the Suffolk County health commissioner, declared an "imminent threat to public health" after receiving approval to do so from the from the New York State commissioner of health. The designation allows the county to address the mosquito issue in an area that would not be accessible without it. The county treated areas of Manorville on Wednesday.

Also, county officials reported that 12 more mosquito samples have tested positive for West Nile virus. The samples, all Culex pipiens-restuans, were collected on Aug. 22 and 24 from Port Jefferson Station, Setauket, Stony Brook, Melville, Bay Shore, Nesconset, Huntington Station, Northport, Greenlawn, South Huntington, and Huntington. To date this year, the county has confirmed that 104 mosquito samples and 10 birds have been positive for West Nile virus. No humans or horses have tested positive in the county this year.

West Nile virus may cause a range of symptoms, from mild to severe, including fever, headache, vomiting, muscle aches, joint pain, and fatigue. There is no specific treatment for West Nile virus. Patients are treated with supportive therapy as needed.

Eastern equine encephalitis is a rare but deadly illness for humans. The disease is also a concern for horses, though a vaccine is available and recommended for horses. Both Eastern equine and West Nile virus are transmitted by the bite of an infected mosquito.

Eastern equine encephalitis is less common in humans because the primary mosquito vector, Culiseta melanura, does not typically feed on humans, Dr. Tomarken said in a statement issued on Thursday. "However," he said, "the virus may be transmitted to humans and horses by bridge vectors, which are other kinds of mosquitoes that have contracted the virus by feeding on infected birds."

Approximately 5 to 10 human cases of Eastern equine encephalitis are reported annually in the United States. New York State has reported 12 cases since 1952. This year to date, there have been no human cases of the virus in Suffolk County. Prior to this year, the last reported positive mosquito for Eastern equine encephalitis in Suffolk County was in 2008.

In severe cases of the Eastern equine encephalitis, a person may experience encephalitis, or swelling of the brain, that may result in death. The mortality rate of those that develop the virus is about 33 percent. There is no human vaccine for it and patients are treated with supportive care.

In 2016, the federal Department of Agriculture reported 118 cases of Eastern equine encephalitis in horses from 15 states, including two from upstate New York. Suffolk County reported three cases of the virus in horses in 2003.