State Health Department Confirms West Nile Virus in Pair of Rockland County Crows

The crows, an adult male and adult female, were submitted from the same area in New City, in the Rockland County town of Clarkstown. The State Health Department's Wadsworth Laboratory confirmed the presence of virus in the bird specimens today, based on positive results of polymerase chain reaction (PCR), immunoflourescent antibody (IFA) and viral culture tests. A gross examination of the birds, called a necropsy, previously was conducted by the State Department of Environmental Conservation's Wildlife Pathology Unit.

Dr. Novello said New Yorkers should not be alarmed by the findings, but they should stay informed, and should take steps to decrease their risk of being bitten by mosquitoes.

"Our test results do not conclusively indicate that there are infected mosquitoes in the area, since we cannot know for certain where the birds acquired the infection, but we wanted to get the word out quickly that people should continue their efforts to protect themselves and their families," Dr. Novello said. "That means eliminating standing water around your home where mosquitoes breed, reporting dead bird sightings to your local health department and taking personal mosquito protection measures, as appropriate."

Personal mosquito protection measures include installing or repairing screens, avoiding likely mosquito habitats, especially between the hours of dusk and dawn when mosquitoes are active and feeding, choosing clothing that provides maximum protection against biting insects and considering the use of an insect repellent containing DEET.

West Nile virus can cause a range of symptoms, from mild to severe illness. In the most serious cases, infection can result in encephalitis, or swelling of the brain. Elderly individuals, or those with compromised immune systems, are most at risk.

During last year's West Nile virus outbreak, 62 people developed encephalitis and seven died. Cases of West Nile encephalitis were confirmed in New York City (including a visitor from Canada), Westchester County and Nassau County. Health officials stress that there have been no known cases of illness caused by West Nile virus among humans this year, and these two birds are the only ones that have been positive of more than 125 tested since January. One hawk that died in February was confirmed positive at a Connecticut laboratory.

Dead birds, especially crows, were present in large numbers in areas affected by last year's West Nile virus outbreak. Crows are particularly susceptible to the virus, and the vast majority of infected crows die. For that reason, they are considered to be an important early warning sign that infection could be present in a specific area.

Birds are not the source of West Nile virus, but rather, serve as its reservoir, after being bitten by an infected mosquito. The Northern House Mosquito, or Culex pipiens, is the species most closely associated with transmission of West Nile virus. Rockland County Health Department staff have collected mosquito specimens (called pools) from each town in the county. Those pools arrived at Wadsworth Laboratory yesterday to be tested for West Nile virus.

Starting this week, the State laboratory began testing mosquito pools from counties in or near the area affected by West Nile virus last year. Pools will be tested weekly through the transmission season. Other counties have been urged to perform "mosquito inventories," that is, to determine the species of mosquitoes present and their breeding sites. These measures, along with dead bird reporting and human case surveillance, are important components of the State's comprehensive West Nile virus response plan that was formulated in collaboration with counties, other State agencies and representatives of environmental advocate organizations.

Some counties, Rockland included, also plan to establish flocks of sentinel chickens to serve as early warning indicators for presence of the virus in a specific location.

Officials stress that the new findings demonstrate the importance of continuing the comprehensive activities outlined in the response plan, especially enhanced public education, surveillance and control. The plan promotes numerous non-pesticide methods of mosquito control, including residential/commercial and municipal control of mosquito larvae to remove or prevent standing water where mosquitoes breed. Use of larvicides to control mosquitoes in the aquatic stage before they become biting adults also is encouraged, since this type of control measure generally has the least effect on non-target species and the environment.

People with questions about West Nile virus, or reports of dead birds, are urged to contact their local health department. Additional information also is posted on the State Health department's web site (

6/9/00-67 OPA