Eastern Equine Encephalitis -- United States, 1989
As of August 31, 11 states have reported to CDC one fatal human
case and 65 equine cases of eastern equine encephalitis (EEE) in
1989
(Figures 1 and 2). The human case, confirmed serologically,
occurred in
an 11-year-old boy in Mississippi who died of encephalitis on
August 6.
Equine cases have been confirmed serologically (40 cases) or by
viral
isolation from brain (25 cases).
Despite the routine application of larvicides and adulticides by
state
and local agencies, pest and vector mosquitoes, including those
that
transmit EEE, have been abundant this year in several eastern
coastal
locations. For example, on Maryland's eastern shore, Aedes
sollicitans
mosquito collections in light traps have exceeded 50,000 per trap
per
night. In late July, an EEE epornitic (i.e., an outbreak in a bird
population) occurred in a pheasant flock on Maryland's eastern
shore,
leading to 20 deaths among approximately 1500 fowl. Four equine
cases
from the DelMarVa Peninsula and on Assateague and Chincoteague
islands
off the Maryland and Virginia coast have been confirmed, and other
clinically suspected cases have been reported from this area.
Emergency
widespread aerial applications of adulticides over Assateague
Island
and adjacent mainland recreational areas were conducted in the last
week of August.
Reported by: State and local health departments. Div of
Vector-Borne
Viral Diseases, Center for Infectious Diseases, CDC.
Editorial Note
Editorial Note: EEE occurs sporadically in the United States,
principally in coastal locations in mid-Atlantic and southeastern
states. In most years, fewer than five human cases have been
reported;
however, clinical disease is associated with a case-fatality rate
of
30%-70%, and most surviving patients have serious neurologic
sequelae
(1-3). EEE in horses is usually fatal.
EEE is transmitted in an enzootic cycle among birds and Culiseta
melanura mosquitoes, an ornithophilic species that seldom bites
people.
Various mosquito species with catholic feeding habits, including
Ae.
vexans, Ae. sollicitans, and Coquillittidia perturbans, are chiefly
responsible for transmitting infections to humans and horses
(1,2,4).
This year, following heavy spring and summer rains, several
northeastern states that continuously monitor vector mosquito
activity
have reported the highest numbers of enzootic and epizootic vector
mosquitoes ever recorded in their areas.
With onset of cooler weather the abundance of mosquitoes is
declining
in many areas of the eastern seaboard; EEE cases generally decline
in
late summer, although cases have occurred as late as mid-October
(5).
No specific preventive or therapeutic measures against EEE are
available. In areas with a potential risk for the disease,
protective
measures against mosquito exposure --including the use of
repellents,
appropriate dress, and avoiding outdoor activity in the evening
(the
peak period of biting activity)--are prudent.
Tsai TF, Monath TP. Viral diseases in North America transmitted
by
arthropods or from vertebrate reservoirs. In:
Feigin RD, Cherry JD, eds. Textbook of pediatric infectious
diseases.
Vol 2. 2nd ed. Philadelphia: WB Saunders, 1987:1417-56.
Przelomski MM, O'Rourke E, Grady GF, Berardi VP, Markley HG.
Eastern
equine encephalitis in Massachusetts: a report of 16 cases,
1970-1984.
Neurology 1988;38:736-9.
Goldfield M, Sussman O. The 1959 outbreak of eastern
encephalitis in
New Jersey: I. Intro duction and description of the outbreak. Am J
Epidemiol 1968;87:1-10.
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