EQUINE INFECTIOUS ANEMIA - USA (MONTANA)

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Date: 14 May 2010
Source: The Horse.com [edited]



Because 2 horses recently tested positive for equine infectious
anemia (EIA) in Montana, the Montana Department of Livestock's Animal
Health Division has scheduled a 17 May 2010 meeting in Gallatin
county to update local horse owners on the situation.

EIA, also called swamp fever, was reported in Gallatin county on 26
Apr 2010 after a horse tested positive following a routine Coggins test.

"The horse was going to be traveling out of state, which is how the
positive came up," said Tahnee Szymanski, DVM, a staff veterinarian
for the Department of Livestock. "As a result of the positive test, 2
more horses on the premises were tested, and we found one other positive."

50 nearby horses were also tested. As of 13 May 2010, about 45 of
those tests had come back, all negative, said Szymanski. She expected
the rest of the test results in the next day or so.

Because of the infectious nature of EIA, horses testing positive must
be euthanized or quarantined for life. The 2 positive horses were
quarantined for transport to an EIA-positive herd. Szymanski
explained that these herds are bled monthly for lab efficiency testing.

"In that way, these animals can contribute to our understanding of
the disease, and they do not have to be euthanized," she said.

EIA is spread by biting insects and through contaminated needles,
said Szymanski.

"We recommend annual testing and like to see horses that travel for
equine-related events tested twice a year," she said. "While Coggins
tests are routinely required for horses traveling out of state, some
boarding facilities and events now require negative Coggins tests as
well. Some farms also require a negative test to bring an animal in
for breeding."

The 17 May 2010 meeting will be held at 10 a.m. at the Gallatin
County Fairgrounds, Building 4.

--
Communicated by:
ProMED-mail

[EIA is a viral disease (EIAV) of members of the horse family.
Identified in France in 1843 and first tentatively diagnosed in the
United States in 1888, it has commanded a great deal of attention
over the years.

EIA is the 1st retrovirus-induced disease proven to be transmitted by
insects (Stein et al. 1942). And EIAV is the 1st persistent virus for
which "antigenic drift" was defined (Kono 1972). (Antigenic drift is
the virus's ability to change its form sufficiently so that it is no
longer vulnerable to existing antibodies.) Finally, EIA is the 1st
retrovirus-induced disease for which a diagnostic test was approved
(Coggins and Norcross 1972).

More recently, the EIAV has been recognized as a lentivirus, the type
that causes slowly progressive, often fatal diseases. It is a close
relative to the human immunodeficiency virus (HIV), which causes
acquired immunodeficiency syndrome (AIDS). In fact, EIAV was the 1st
virus shown to be related to the HIV through cross-reaction in tests
of blood serum (Montagnier et al. 1984). These 2 lentiviruses share
many structural and biochemical features, and EIAV is thought to
serve as a useful model for many aspects of HIV research, especially
for discovery of common mechanisms of immunologic control (Montelaro
and Issel 1990).

An effective test for antibodies specific to EIAV was described in
1970 by Leroy Coggins, D.V.M. for collaborators (Coggins and Patten
1970) and was rapidly adopted by authorities around the world. The
agar-gel immunoddiffusion (AGID) or Coggins test was shown to
correlate with horse inoculation test results for EIAV and,
therefore, could be used to identify EIAV carriers (Coggins et al.
1972). Because only members of the horse family were shown to be
infected, programs based on serologic testing were designed and
adopted to help control the spread of EIAV (Campbell 1971).

When horses are exposed to EIAV, they may develop severe, acute signs
of disease and die within 2 to 3 weeks. This acute response is rarely
seen in natural situations, where blood-feeding insects transmit low
doses of virus.

Nonetheless, this form of the disease is the most damaging and the
most difficult to diagnose because the signs appear rapidly, and
often only an elevated body temperature is noted. At this early stage
of the infection, the horse usually tests negative for antibodies to
EIAV, and blood samples must be collected at a subsequent date
(generally 10 to 14 days later) to confirm or exclude EIA as a
diagnosis. During this period, it is prudent to quarantine the horse
(or the farm) if EIA is strongly suspected on the basis of history or signs.

The clinical signs of the acute form of EIA are rather nonspecific,
and in mild cases, the initial fever may be short lived (often less
than 24 hours). As a result, horse owners and veterinarians may not
observe this initial response when a horse is infected with EIAV.
These infected horses often recover and continue to move freely in
the population. The 1st indication that a horse was exposed to and
infected with EIAV may well be a positive result on a routine annual test.

Fever - An infected horse's temperature may rise suddenly to about
105 F or, rarely, as high as 108 F. Then, it may drop back to normal
for an indeterminate period until the onset of another episode.

Petechial hemorrhages - Minute, blood colored spots appear on the
mucous membranes.

Depression - The horse appears more or less dejected (head hangs low)
and generally listless.

Weight loss - The horse may refuse feed or may eat an inordinate
amount but still continue an obvious decline from normal weight.

Dependent edema - The horse may develop swelling, evidence of fluid
collecting under the skin in the legs, under the chest and other
underbody surfaces.

Anemia - The horse's blood may have a marked drop in its red
corpuscle count and appear thin and watery. The animal may also have
an irregular heartbeat, and a jugular pulse may become evident.

The horse with chronic EIA is the classic "swamper," who has lost
condition, is lethargic and anorexic, has a low hematocrit, and
demonstrates a persistent decrease in the number of blood platelets
(thrombocytopenia), especially coincident with fever induced by EIAV
(Clabough et al. 1991).

EIA is considered a classic blood-borne infection. People have played
an important role in EIAV transmission over the years by using
blood-contaminated materials on different horses. Although this mode
of transmission was more prevalent before serologic tests to identify
EIAV carriers were available, it is wise for owners and veterinarians
to apply the same universal precautions that are used to reduce the
risk of spreading blood-borne disease agents in humans (U.S.
Department of Labor 1992).

The EIAV most frequently is transmitted between horses in close
proximity by large biting insects, such as horse flies and deer flies
(tabanids), which inflict painful bites (Issel and Foil 1984). The
bites from these tabanids stimulate defensive movement by the horse,
which often results in an interruption of the blood-feeding. When
interrupted, the fly is motivated to complete the feeding as soon as
possible. It then attacks the same or a 2nd host and feeds to
repletion. In this manner, any infective material from the blood of
the 1st host which is present on the mouthparts of the insect can be
mechanically transmitted to the 2nd host.

Controlling the spread of EIAV involves minimizing or eliminating
contact of horses with the secretions, excretions, and blood of
EIAV-infected horses. This has been accomplished in most areas of the
world by testing and segregating test-positive horses from those that
are test-negative. When this separation is done, it is imperative to
retest the test-negative band at 30- to 60-day intervals until new
cases fail to appear. Once the reservoirs of EIAV are identified,
separated, and maintained a safe distance from other horses, the
transmission of EIAV is broken. This sounds easy, but until all
horses are tested, one must assume that each horse is a potential
reservoir of EIAV and take precautions to commingle only horses whose
background is impeccable, i.e., they come from farms where only
test-negative horses are found and have never been exposed to
test-positive horses or other equids.

This comment has been extracted from:
.
- Mod.TG]

[see also:
Equine infectious anemia: resources available 20100415.1226
2007
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Equine infectious anemia - USA (NM ex TX) 20070831.2872
2006
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Equine infectious anemia - USA (VA) 20060803.2154
2002
---
Equine infectious anemia - USA (Georgia) 20020825.5148
Equine infectious anemia, law change - USA (Texas) 20020501.4062
2000
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Equine infectious anemia - USA (Montana) (02) 20000624.1040
Equine infectious anemia - USA (Montana) 20000619.0998
1999
---
Equine infectious anemia - USA (New York) 19991129.21032
Equine infectious anemia - USA (Utah) 19991127.2092
Equine infectious anemia - USA (Penn.) 19991104.1978
Equine infectious anemia - USA (Virginia) 19990921.1684]
...............................................tg/msp/dk

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