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NJDA Alerts Veterinarians to Symptoms of West Nile Virus
For Immediate Release: September 28, 1999 Contact:

Hope Gruzlovic


The NJ Dept. of Health and Senior Services issued an advisory on Saturday, September 25th, regarding the identification of a West Nile-like virus [WNV] from several bird specimens originating from the New York City area. Prior to the identification of this virus, recent cases in humans and birds in New York have been attributed to the closely-related St. Louis encephalitis virus. To date, there have been no cases of any encephalitis virus detected in NJ, but this memo provides information which will be helpful when dealing with suspect cases and concerned horse owners. WNV is an arbovirus and is closely related to the equine encephalitis viruses: eastern, western and Venezuelan. Most importantly, the vaccines administered to horses to protect them from the equine encephalitis viruses will not protect them against WNV. Among animals, horses are known to exhibit clinical signs of infection, although birds and other mammals can be infected. The significant die-off of birds in and around NY, predominantly crows, is suspected to be the result of this newly introduced virus to a naive population. The Division of Animal Health recommends that you include WNV in your differential diagnosis in any horse exhibiting neurological signs until after the first frost. As with the other encephalitis viruses, report your suspicions to the Division of Animal Health immediately [609-292- 3965]. Initial serum samples should be submitted followed by convalescent samples and submissions of brain tissue for virus isolation when indicated [samples sent on ice]. Questions regarding this process should be directed to the Division (phone (609) 984-2251; fax (609) 777-8395). Since no vaccine exists to protect horses from WNV, preventing exposure will be especially critical if the virus crosses into NJ. When possible, horses should be housed indoors during the mosquitos' feeding periods: dawn and dusk. In addition, sheets and insect repellents should be utilized. If newly-discovered dead birds are found, contact local health officials. Some birds may be needed for laboratory testing. Gloves should be worn when handling bird specimens. Horses, unlike birds, are a dead-end host and do not pose a direct hazard to humans, if infected. WNV has been previously isolated in several countries of the Mediterranean basin, Romania and France. The most recent epidemic of WNV occurred from August-October 1998 in France. All horses affected were stabled near wetlands. Like the other encephalitis viruses, WNV is transmitted by mosquitos. Clinical signs in the horses began with ataxia, degenerating to paralysis, including flaccid paralysis of the lower lip, coma and death. Fever was NOT routinely observed in the affected horses. 42% of the horses in this outbreak [6 of 14] died or were euthanized as a result of the disease while 57% of the surviving horses reportedly made a complete recovery.

The NJ Mosquito Commission has not identified any encephalitis viruses in mosquitos this year. As you are aware, the equine encephalitis virus vaccines are effective for 4-6 months. Boosters should be given at the suggestion of the local veterinarian, but will not protect against this newly identified virus.