The first Suffolk County mosquito sample to test positive for West Nile virus this year was reported Friday by county health officials.
The sample was collected June 18 in South Huntington, officials said.
No positive samples have been reported in Nassau, a spokeswoman said.
Some mosquito bites can transmit West Nile to humans, with mosquitoes picking up the virus by feeding on infected birds.
"The confirmation of West Nile virus in mosquito samples or birds indicates the presence of West Nile virus in the area," said Dr. James L. Tomarken, county health services commissioner.
"While there is no cause for alarm, we urge residents to cooperate with us in our efforts to reduce the exposure to the virus, which can be debilitating to humans."
In some cases, the virus causes serious neurological illnesses that can lead to health conditions or death.
According to the New York State Health Department website, Nassau had two reported human cases of West Nile and no deaths last year, as of October 28, 2014. In December, Suffolk County reported one case and no deaths.
Last year, 2,205 cases of human infection were reported in the United States, resulting in 97 deaths, according to the federal Centers for Disease Control and Prevention.
Residents are advised to eliminate stagnant water where mosquitoes breed in and around their homes; to minimize outdoor activities and cover their skin in the evening and night when mosquitoes are most active; and to use mosquito repellent outdoors.