One more mosquito sample has tested positive for Eastern equine encephalitis, a rare but potentially deadly virus, Suffolk County health officials said Friday.

The most recent sample, collected Aug. 29, brings the number of positive samples to four this season, all from the Culiseta melanura species and all collected in the Manorville area.

The county conducted aerial spraying Aug. 30 in areas of Manorville and Calverton with an eye to controlling adult mosquitoes, after Suffolk Health Commissioner Dr. James Tomarken’s declared an “imminent threat to public health” on Aug. 25. That declaration triggered emergency state funding to fight the spread of the virus, allowing the county to take action to control mosquitoes in Manorville and the vicinity, officials said.

No samples in Nassau have tested positive for equine encephalitis so far. There have been no human cases reported in either county.

Spread by bites, the disease is also a concern for horses, but while there is a vaccine for those animals, none exists for humans.

The illness is less common in humans because the primary mosquito carrying the virus, Culiseta melanura, typically does not feed on people, health officials said.

Tomarken said other mosquitoes can carry the virus by feeding on infected birds.

Symptoms include headaches, high fever, chills and vomiting, and encephalitis can be deadly, causing a swelling of the brain in severe cases, officials said. About 33 percent of people who develop Eastern equine encephalitis die.

New York State has reported 12 human cases since 1952.

Suffolk health officials on Friday also said that six more mosquito samples have tested positive for West Nile virus, five Culex pipiens-restuans and one Culex salinarius, collected Aug. 29 and Aug. 31 in Setauket, Lindenhurst, Huntington, Northport and Copiague.

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That brings the total number of mosquito samples testing positive this year for West Nile virus to 110. No humans or horses have tested positive in Suffolk, officials said.

Nassau County has had 68 mosquito samples testing positive for West Nile, a health department spokeswoman said, with two human cases.

In one case the person was not hospitalized, and in the second the person was hospitalized and discharged, she said.

— With Ellen Yan