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.
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.