West Nile and Zika viruses are spread by mosquitoes. While the Health Department has no record of New Yorkers contracting either virus this year, West Nile was detected in Staten Island mosquitoes last week. View Full Caption Wikimedia Commons

NEW YORK CITY — Chemicals aimed at killing mosquitos will be dropped in four boroughs this weekend in an effort to prevent Zika and West Nile.

Low-flying helicopters are expected to drop larvicide pellets over three days in areas where West Nile has been detected in the past and in other marshy mosquito breeding areas, according to a Health Department spokesman.

The following neighborhoods, among other areas, will be treated Friday to Sunday between 6 a.m. and 7 p.m., according to the Health Department's website:

• Marine Park (Brooklyn)

• Kissena Park (Queens)

• Pelham Bay Park (The Bronx)

• South Beach (Staten Island)

The larvicide treatments are part of a $21 million strategy to fight the Zika virus in New York City over the next three years.

This is the third larvicide treatment session of the summer. The agency conducted two other drops in mid-May and early June.

The department made the anti-mosquito treatment announcement the same day the Office of Emergency Management staged a day of Zika prevention.

Officials visited 20 subway stations during rush hour on Wednesday to hand out pamphlets on Zika-prevention and to urge women who traveled to Zika-affected countries while pregnant to seek medical attention.

“Our main message today is that if you are pregnant or want to become pregnant, do not travel to a Zika-affected country,” said the city's Health Commissioner Dr. Mary T. Bassett.

“If there is one year to reconsider a vacation to a Zika-affected country, this is that year.”

There have been no transmissions of the Zika virus in New York City, but the West Nile Virus had been detected in mosquitoes on Staten Island last week, the agency announced on Monday.

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