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Equine
Viral Arteritis (EVA) is a contagious disease of horses, mules, zebras,
and other equids. As the name indicates, it is caused by a virus.
It
is often a mild disease characterized by fever, depression, and swelling
(edema) in the lower limbs and lower chest and abdomen. In healthy
horses, EVA is usually not too much of a problem, although it can vary
from an infection with no signs of illness to severe disease that
includes a great deal of edema, respiratory problems, and even some
central nervous system signs such as ataxia (incoordination). The
primary concern, however, is the reproductive problems that are
associated with the disease.
These
reproductive problems include abortions and a possible period of
subfertility in the stallion. Consistent with many diseases, clinical
signs of the disease are more severe in the very young and the very old.
Although death is rare, it had been reported in young foals as a result
of severe pneumonia or a combination of pneumonia and intestinal
inflammation.
The
equine industry in the United States has traditionally attached little
significance to the disease. However, since an epidemic of the disease
in Kentucky in 1984, EVA has had a significant impact on international
trade of horses and equine semen. The United States currently does not
have an import control policy for EVA, but all other major
horse-breeding countries have policies that deny entry of carrier
stallions and EVA-infective semen. According to the USDA, efforts to
gain a greater level of control over the dissemination of EVA within the
country’s equine population have been hampered by a lack of awareness
of the disease and its potential consequences in the horse industry.
In
1998, Alabama participated in a study conducted by the UDSA that, among
other things, questioned randomly selected horse owners about their
knowledge of EVA. Like most owners in other states that participated,
those in our state indicated that most had only heard of EVA with little
knowledge of the disease or had no knowledge about it at all. Another
finding in this National Animal Health Monitoring System study indicated
that on random blood sampling for EVA, there was a low seroprevalence,
meaning there was very little exposure to the virus in our country.
Because they have never been exposed to the virus, the vast majority of
our nation’s horse population could be considered completely
susceptible to natural infection.
The
virus can be found in many countries of the world with Japan and Ireland
being exceptions. Outbreaks of the disease are not very common, but are
usually associated with the movement of horses or shipping of semen.
Outbreaks that have occurred may be widespread, but the majority of the
horses infected may never show signs of illness.
Aerosol
is the primary mode of transmission, although it can be transmitted
venerally, from dam to offspring, or indirectly through the environment,
on feed or other materials. Aerosols from acutely infected horses are
responsible for the widespread dissemination of the virus at racetracks
and other places horses are congregated. Mares, geldings, and young
colts that become infected usually clear the virus from their body after
a period of time. After the incubation period of 3-14 days, the actual
time that signs of disease may be present is 2-9 days. Stallions,
however, often develop into carrier states in which the virus may exist
for years in the otherwise healthy animal. Carrier stallions may
constantly shed the virus in their semen for years. Therefore, when
susceptible mares are bred by these stallions either naturally or by
artificial insemination, they often become infected with EVA.
In
late June of this year, the New Mexico Department of Agriculture and
their State Veterinarian announced an outbreak of EVA in their state.
According to the New Mexico State Veterinarian, one ranch was
quarantined and others voluntarily restricted movement in order to stop
the dissemination of the disease. They are still in the process of
investigating where the virus may have come from and how it may have
infected the horses involved. There are no specific numbers of horses
infected or other information available. The important point to remember
is that New Mexico animal health officials have taken actions to stop
the spread of the virus.
What
happened in New Mexico is a reminder that we as horse owners should
remain vigilant against the spread of disease, whatever it may be. It is
important to always practice good biosecurity measures, such as
separating horses that are introduced or reintroduced into your herd
after being commingled with other horses. While this may not be
practical, it is ideal. Beyond that, it is important to notify your
veterinarian when signs of illness do occur. Your veterinarian should be
able to determine whether there is a need to submit samples or test for
diseases that could be move of a problem than the original appearance
might indicate. |
