—Lancaster Farming, Saturday, October 6, 1973
52
Why Vaccinate For VEE
With no confirmed cases of
Venezuelan equine encephalitis
(VEE) in this country since 1971
and none in Mexico since 1972,
horse owners may ask, why does
the U. S. Department of
Agriculture (USDA) continue
recommending vaccination of
horses for this disease?
Officials of USDA’s Animal and
Plant Health Inspection Service
(APHIS) point out that VEE-a
mosquito-borne virus disease
that is usually fatal to horses and
causes flu-like symptoms in
humans-can strike suddenly,
moving with giant strides when
weather and other conditions are
ripe. Migration of the virus oc
curs through travel of infected
animals or the virus-carrying
mosquito.
VEE was little known outside
of northern South America until
1969. In that year, an epidemic
leapfrogged over Panama into
Guatemala; and from there it
spread rapidly through Central
America and Mexico. By late
June 1971, it was in southern
Texas--having migrated over
2,500 miles in two years.
VEE in Texas was quickly
controlled and confined to 26
southern Texas counties, but not
before hundreds of horses died
and a number of people became
ill. Emergency measures,
coordinated by USDA, included
mass vaccination of horses,
aerial spraying to kill adult
mosquitoes, and quarantines to
limit horse movements.
By the end of 1971, over 2.8
million horses had been
cinated in 19 states--from
California to the Carolinas, and
up the eastern seaboard to New
Jersey
APHIS officials pointed out
that 1972 was a year of intensive
surveillance for VEE With other
agencies, colleges and univer
sities assisting, APHIS collected
over one million mosquitoes and
over 15,000 blood serum samples
from ammals-for laboratory
analysis to detect VEE virus
Although the U S had no VEE
in 1972, horses in Califoriua and
Arizona were threatened last
summer when a rash of out
breaks occurred in nearby areas
of western Mexico. Mexico
carried out a vigorous vac
cination program to eliminate the
outbreaks
According to recent statements
by Mexicans authorities, the last
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confirmed VEE case in Mexico
occurred Sept. 19, 1972. The last
confirmed case in this country
occurred Nov. 11, 1971 in Starr
County, Texas, near the U.S. -
Mexico border.
Also last year, over 1,000 cases
of suspected encephalitis in
horses were investigated
throughout the United States. All
findings were negative for VEE,
but 452 cases of western equine
encephalitis (WEE) and 32 cases
of eastern equine encephalitis
(EEE) were confirmed by the
APHIS diagnostic laboratory at
Ames, lowa.
The eastern and western types
of equine encephalitis have been
known in this country for many
years. As recently as the 1930’5,
epidemics of these diseases
caused severe losses of horses,
mules and other equine animals
in midwestern states, California,
and along the eastern seaboard.
Development of effective vac
cines for these diseases has
greatly reduced the severity of
EEE and WEE outbreaks.
So far this year, EEE cases
have been confirmed in many of
the eastern and southeastern
states, and WEE cases have been
confirmed in several western
states. But no VEE.
To detect any VEE virus
movement from previously in
fected areas in Mexico, mosquito
traps are being monitored along
the entire U. S.-Mexico border.
The area from Brownsville to
Laredo, Texas is being monitored
by the Entomology Department
of Texas A & M University. USDA
is handling the rest.
Mosquitoes are frozen and sent
to the Ames laboratory or to the
Texas A & M laboratory where
they are checked for all three
types of equine encephalitis, plus
other arbovirus diseases (those
transmitted by mosquitoes or
other blood-sucking insects). So
far, WEE virus has been detected
in trapped mosquitoes, but no
VEE virus has b§en found.
Dr. E.E. Saulmon, Deputy
APHIS Administrator for
Veterinary Services, believes
that checking mosquitoes is a
good detection method. “This can
provide an early warning of virus
activity,” he said, “and it’s less
expensive than sampling blood
serum from horses and other
animals as was done so ex
tensively last year,”
But APHIS officials say,
having a surveillance or warning
system doesn’t mean horse
owners can forget about vac
cination. USDA strongly
recommends vaccination to
protect horses from VEE. VEE
vaccine provides protection for at
least 18 months and possibly
longer.
APHIS officials also recom
mend that horse owners have
their animals vaccinated for
EEE and WEE, remembering
they need annual booster shots.
It’s important to note, however,
that vaccines for EEE and WEE
do not protect against VEE; and
likewise, VEE vaccine does not
protect against the other two.
Dr. Saulmon credits the vac
cination efforts of the Mexican
government in helping to protect
U.S. horses against VEE.
Mexican authorities conducted
vigorous vaccination campaigns
in 1970, 1971 and 1972. In the first
half of this year, their vac
cination teams inoculated more
than two million horses, mules
and burros. The VEE vaccine
used was produced in Mexico
from seed virus furnished by the
United States.
Clinical signs of the three types
of equine encephalitis-fever and
incoordination--are in
distinguishable in horses. This
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means that an accurate diagnosis
depends upon laboratory tests,
say APHIS 011101318" Also, all
three types affect humans as well
as horses. But there are some
significant differences between
VEE and the other types.
For instance, VEE virus
multiplies so rapidly in horses
that mosquitoes biting infected
horses at certain disease stages
are likely to pick up the virus and
pass it to susceptible (non
vaccinated) horses, or to
humans.
So horses play an important
role in the spread of VEE, but
they do not play a similar role in
the spread of EEE and WEE.
These diseases are usually
maintained by birds that carry
the viruses. Mosquitoes transmit
eastern or western viruses from
birds to horses or humans.
It’s a fact that EEE or WEE
may strike only one or two horses
in a large susceptible herd, while
VEE would be likely to sweep
through the entire herd. It’s also
a fact that vaccinating a horse for
VEE not only protects that horse
but eliminates a potential source
of disease spread.
Another thing that sets VEE
apart from the other tvnes of
encephalitis in horses is the
variety and prevalence of
mosquitoes capable of spreading
VEE. Over 30 species have this
capability, and they are found in
all regions of the country.
Significantly fewer species of
w
mosquitoes figure in the spread
of EEE and WEE.
The mosquito’s role in
spreading VEE*and the other
types of encephalitis is not
merely mechanical. The
mosquito is a biological vector,
meaning the virus actually
multiplies in the mosquito’s
system-in the salivary glands.
A few days after ingesting the
virus, the mosquito develops its
ability to transmit virus to the
animals on which it feeds. It can
transmit the virus with great
efficiency for the rest of its life-a
matter of weeks for some species
and months for others.
“Considering that less than
half of the nation’s horses
estimated at six to six and a half
million-are not yet vaccinated
for VEE, and knowing the ability
of VEE virus to migrate long
distances quickly,” Dr. Saulmon
said, “I strongly recommend that
all horses be vaccinated for VEE
as well as for the eastern and
western types of equine en
cephalitis,”
The phrase “catch as catch
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a style of wrestling.