With 12 new mosquito samples testing positive for West Nile virus, the total for the year is now up to 18 in Suffolk County, health officials reported on Friday.

The new samples, all Culex pipiens-restuans, were collected July 20 and 21 in Farmingville, Selden, Port Jeff Station, Stony Brook, Huntington Station, Northport, Greenlawn, Commack, Shelter Island, and Holtsville.

Two birds, one in Yaphank and one in East Northport, have also tested positive for the virus, officials said in a news release.

Nassau County is reporting one positive mosquito sample, collected June 29 in Farmingdale, a health department 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, Suffolk 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.”

The virus may cause serious neurological illnesses that could lead to health conditions or death, health officials say.

Last year Suffolk County saw five human West Nile cases and no deaths, with Nassau reporting 9 human cases and no deaths.

Also last year 2,060, human cases of West Nile were reported in the United States, resulting in 119 deaths, based on information as of mid-January 2016, according to the Centers for Disease Control and Prevention.

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Health officials say residents can help make areas around their homes unfriendly to mosquitoes by:

•Regularly looking for and eliminating even the smallest amounts of standing water, which is where the insects reproduce. That could include in cans, buckets and other containers, as well as old tires, tarps, pool covers and children’s toys.

•Drilling drainage holes at the bottom of garbage cans, changing birdbath water at least weekly and making sure roof gutters are unclogged and draining properly.

•Adding fish to circulate water in any backyard ponds, and clearing pond edges of debris and vegetation.