Equine Infectious Anemia (EIA) and
the Coggin's Test in Horses
Robert N. Oglesby, DVM
Equine Infectious Anemia is a viral disease of horses for
which there is no cure, nor is there a vaccine to prevent this disease. Equine
infectious anemia is a disease of horses characterized by three clinically
distinct forms. That range from a rapidly worsening febrile disease that results
in death to a unapparently ill chronic carrier form. First described over 150
years ago in Europe, the disease has been seen in the United States for more
than 75 years. In 1970 an agar-gel immunodiffusion (AGID) test, the Coggins
test, capable of detecting inapparent virus carriers. This test, along with
improved knowledge about EIAV transmission, has made effective control of the
infection among horse populations a reality. This article discusses how horses
get this disease, clinical signs, testing for EIA and its reliability, and the
handling of infected horses.
understanding the importance of the Coggins Test
by Mark A.
EIA (Coggins) blood test is required on horses before most organized events,
and for transporting a horse from one state to another. Nearly everyone has
dealt with it, but many owners don't know exactly what it is.
The test is a
check for equine infectious anemia, a contagious disease that affects horses
worldwide. It is also known as "swamp fever" because of the higher incidence
on the Gulf Coast of the United States, where increased humidity and
temperature are favorable for transmission of the disease.
There is no
treatment known to cure or eliminate the virus. Additionally, studies to
develop an effective vaccine have been disappointing. EIA is caused by a
virus that was first identified in 1904. Although this disease has affected
horses for a long time, researchers have recently grown more interested
because the EIA virus is closely related to the human immunodeficiency virus
transmitted primarily by bloodsucking insects. The horsefly is the most
common. The large size and painful bites of these flies make it unlikely that
a horse would permit them to complete a blood meal uninterrupted; by tail
swishing or twitching, they send the biting fly on its way. This is the
problem, however, because the virus is transmitted to other horses when the
horsefly starts his meal on an infected horse and completes it on an
EIA has three
common clinical forms.
In the acute
or early form, the horse will be depressed, uncoordinated and feverish. Horses
are rarely anemic during this stage. This phase may last several days and is
the stage during which the horse is most likely to transmit the disease to
phase is characterized by weight loss, recurring fevers and general weakness.
Anemia is likely to be present, and mares can abort during this stage.
survive the first two stages, they enter the final or chronic stage, where
they often appear normal. An owner may report that a horse is a poor keeper,
and the animal may be mildly anemic. Infected mares can transmit the disease
to their foals.
infected with the EIA virus will be a carrier of the disease for life.
Although horses in the chronic stage appear normal, they become ill again if
subjected to stress, such as shipping or severe weather. Carriers pose a
health threat to the equine community. Since the early 1960's, several
outbreaks of EIA have occurred at either race tracks or large breeding farms,
resulting in the deaths of many horses.
test, developed in the 1960's by Dr. Leroy Coggins, is based on the detection
of antibodies in the horse's blood. Once a horse is infected with EIA the
antibodies will be present in the blood for life. THE USDA does not have an
eradication program for EIA--however, a national approved laboratory system
has been established to perform the Coggins test.
Even if you
don't show your horse, it should have an annual Coggins test. Horses that are
shown or transported regularly may require more frequent testing.
require that horses entering or being transported across their lines have a
negative Coggins Test no more than six months old. Interstate transport of
horses with a positive Coggins test is prohibited. Likewise, many horse shows
and other events require a negative Coggins for your horse.
If a horse
tests positive, strict quarantine measures are imposed. These include
confinement in a screened stall and a 200-yard buffer from all other horses.
Often, owners elect to euthanize their horses rather than subjecting them to
such strict isolation.
the relatively low incidence of EIA in the United States, most horse owners
and veterinarians have decided that additional regulations are not necessary.
Last year, 76,000 horses were tested in Kentucky, with 20 horses testing
Coggins-positive. In Virginia, 40,000 were tested, with eight positives.
Nevertheless, if you plan to buy a horse or board a horse, require either a
recent negative Coggins from the owner, or isolate the horse until the test is
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