It's believed someone in the Hudson Valley donated blood without knowing they were infected with the West Nile Virus.

During the last week, a West Nile Virus presumptive viremic donor from Ulster County was reported to the CDC, according to the New York State Department of Health's weekly report. The New York State Department of Health works with local health departments to track mosquitos and releases a weekly surveillance report.

Presumptive viremic blood donors are people who had no symptoms at the time of donating blood through a blood collection agency, but whose blood tested positive when screened for the presence of West Nile Virus, the CDC reports.  Some donors develop symptoms after their donation.

It's not clear where or the exact date when someone from Ulster County donated blood infected with the West Nile Virus.

The Hudson Valley is seeing human cases of the West Nile Virus at alarming rates this summer. Last week, one person from Dutchess County and another from Ulster County tested positive for the virus. This year, human cases of the West Nile Virus was reported in Orange, Ulster, Rockland and Westchester counties.

A bite from an infected mosquito can spread West Nile Virus, an infection that can cause serious illness, and even death. One in five infected people develops a fever and other symptoms. One out of 150 infected people develops a serious, sometimes fatal illness, according to the CDC.

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