New York State Health Commissioner Antonia C. Novello, M.D., M.P.H., Dr. P.H. announced July 17 that the State Health Department for the first time this year has identified preliminary evidence of West Nile virus in mosquitoes by using a rapid, highly sensitive DNA PCR molecular technique.

The finding of positive mosquitoes, given the previous discovery of infected birds in Rockland, Westchester and Suffolk counties, New York, and Bergen County, New Jersey, is not surprising. The pools of mosquitoes that tested positive were submitted by Westchester and Suffolk counties the second week of July, and included pools of Aedes japonicus and a mixed Culex pipiens/restuans complex.

In addition, four more American crows tested positive for West Nile virus. Two crows were from Staten Island and another two came from Clarkstown, Rockland County. This brings the number of birds testing positive for West Nile virus to 19 for the year (16 confirmed and three presumptive, including 14 American crows, three blue jays and two red tailed hawks.) Eleven of the birds are from Rockland, three are from Suffolk, three are from Westchester and two are from Staten Island. To date, the Health Department has tested specimens from more than 700 birds of different species, more than 14,500 pools of mosquitoes from different regions and more than 200 humans. There have been no positive human or equine cases so far.

This is the first time that the virus has been isolated from the Aedes japonicus mosquito. This Aedes japonicus mosquito originated in Asia (Japan, Korea) and is suspected to have arrived in the Northeast in the past few years in shipments of used tires. Since then, it has spread rapidly in Connecticut, New Jersey and New York. Its role in the transmission of the West Nile virus is unknown at this time