Ian Keyser
11/26/12
VB SC 303
Prevention Strategy Paper
Equine Infectious Anemia
The equine industry is involved in many sectors of the economy including agriculture,
business, sport, entertainment, recreation, and medicine. This industry therefore plays an integral
role in the United States’ economy. Today, there are over 9 million horses in the U.S. and over
4.5 million Americans involved in the equine industry.i In fact, if spectators were taken into
account the number of Americans involved in the equine industry would rise by tens of millions
of people.ii Therefore, it should be of no surprise that horses are responsible for a gross economic
effect of over 100 billion dollars.iii With such an enormous economic impact, it is imperative that
the health and wellbeing of the equine species is ensured. Of the numerous diseases threatening
equine health, equine infectious anemia (EIA) is of growing concern. Equine infectious anemia
is highly infectious disease that has the potential to spread rapidly throughout the equine species
and cause devastating losses to the equine industry. In order to prevent outbreaks and in an effort
to eradicate this disease, a proper prevention and eradication program should be enacted. In the
following pages, the epidemiology of EIA is described and an effective program outlined. With
an enhanced knowledge of equine infectious anemia and diligent prevention efforts, this disease
can be effectively managed with the eventual goal of being eradicated from the United States.
“Equine infectious anemia is an infectious viral disease of equidae characterized by a
variety of symptoms related to anemia that accompany either an acute, subacute or chronic
illness that may terminate in death.”iv This disease does not infect humans and is limited to only
the equidae family. EIA has been reported around the globe including almost the entirety of the
South American continent, parts of Asia, much of Europe, and Australia.v All North American
mainland states as well as the majority of the Canadian provinces have reported at least one case
of EIA.vi Approximately 600,000 to 900,000 horses are tested annually in the United States with
the prevalence of disease reported as being less than .5%.vii These results were obtained through
serological testing via the Coggins AGID test and immunoenzymatic tests (ELISA) which are
the two most commonly used and accepted tests for EIA.viii
Equine infectious anemia is a retrovirus disease that belongs to the same family of viruses
as HIV, the lentiviruses. EIA has a variable incubation period that can last anywhere from a few
days to greater than 40 days.ix Once infection takes hold, the virus becomes viremic during
fevers and spreads throughout the equid’s body. Replication of equine infectious anemia occurs
within the host’s own tissue macrophages, which allows the disease to replicate without the
hindrance of the humoral immunity.x High immune build up leads to damage to
glomerulonephritis and vascular damage within the host.xi The anemia by which this virus gets
its name is caused by immune mediated hemolysis and thrombocytopenia.xii The virus further
causes damage by reducing erythropoiesis and reducing plasma iron turnover within the bone
marrow.xiii The virus will then sequester in the serum, liver, spleen, lympthnodes, bone marrow,
lung and kidney of its host.xiv In addition, the virus has been found in milk, feces, semen, and
saliva of infected horses however its survivability outside of the body is greatly reduced. xv
Ultimately, the form of disease the virus produces is a result of the size of infective dose, the
strain of the EIA virus, the antibody levels in the donor horse, as well as the physical stress of the
infected horse at the time of exposure.xvi It must be noted however that once infection has been
established, regardless of clinical disease signs or the severity of the infection the virus will
persist for life within the infected equid.
Acute forms of this disease are marked by the rapid onset of a fever of over 104 degrees
Fahrenheit and a rapid deterioration of physical condition. Muscle weakness of varying degrees
is usually present including staggering gait and tremors. In addition, jaundice of muscosas and
edemas of the lower body are also often present.xvii Tachycardia, arrhythmia and other heart
irregularities are also common. As one might suspect, a key sign of the acute form of this disease
is a severe anemia associated with low hemoglobin values as well as low red blood cell counts.
This acute form produces a mortality rate of around 30% which is associated with the severe
anemia.xviii Those animals that do recover from this form are plagued with consistent attacks of
fever and fluctuate between acute, subacute, and chronic forms of this disease for the remainder
of their lives. The subacute signs are very similar to that of the acute signs with the exception
being that they are less severe and result in lower mortality rates.
Chronic forms of this disease follow the acute or subacute episodes. Considered a lull
period of the disease, the chronic form may reproduce acute or subacute forms of this disease
during times of decreased immunity in the infected host. The clinical signs of this form of the
disease are less severe and include a general lack of stamina combined with periodic anemia
signs.xix Many infected equids may appear to have completely recovered from this disease and
may be asymptomatic. Despite a lack of clinical signs, the animal is still infected and the blood
from these animals can still transmit the infection. These asymptomatic horses can potentially
suffer relapses after many years of being symptom free. These reoccurrences of disease are often
associated with increased stress on older animals as well as the presence of other diseases which
depress the immune system. Upon necropsy, there may be petechial hemorrhages of the spleen
and kidneys, various thromboses as well as lesions of the spleen, liver and lymph nodes with an
emphasis on abdominal lympthnodes.xx
One of the major concerns with equine infectious anemia is the ease with which it can be
transmitted amidst the equine population. Resembling the human immunodeficiency virus, HIV,
EIA can be spread through bodily secretions, primarily the blood. This disease is an epizootic
disease in which hematophagous insects serve as an important mechanical vector. It is important
to note that the EIA virus does not seem to multiply within insects which would therefore only
serve as vectors and not reservoir hosts. Perhaps a bit ironic, it is the horse’s own defense
mechanisms that help spread EIA. Take a horse fly as an example. When the horse fly seeks to
feed it must land on the horse and insert its mouth into the horse’s skin in order to access the
blood. This invokes a pain response in the target organism. In response to this pain signal, the
horse flicks its tail at the fly. To avoid death, the fly stops feeding and flies away. It is at this
moment that transmission is a concern since the virus has been shown to be capable of surviving
as long as four hours within an insect’s mouth.xxi If the blood consumed does not satisfy the fly
it will seek to feed again. If there are any nearby horses then they may be chosen instead of the
original horse. There will be trace amounts of the initial horse’s blood still in the insect’s mouth
when it re-feeds and thus, transmission occurs. Once infected the horse becomes a host for the
virus and can, in turn, infect many other horses over a very short period of time. Amongst the
blood feeding insects, the stable fly and various horse flies are the most common vectors.xxii
Since this disease can be transmitted through the blood it is not inconceivable that transmission
could occur during exposure to injured hosts of the disease. Of special note, tack and bridles pose
a threat to spread EIA. In addition, iatrogenic transmission can occur from infected instruments,
needles etc. that are used on infected equidae. Since the virus has been found in the semen and
milk of diseased equids, the disease may be transmitted through sexual intercourse and during
nursing. Recent evidence also suggests that foals can be infected in utero and thus reproduction
in infected female animals can also transmit this disease prior to nursing.xxiii
The most effective diagnosis of equine infectious anemia can be performed through
serological tests. These tests are the best way to diagnosis EIA as the signs of this disease so
strongly resemble those of various other diseases. In fact, when diagnosing this disease
differential diagnosis should be performed against all other diseases that produce the clinical
signs of fever, edema, and anemia. A few of the diseases that should be tested for include:
babesiosis, leptospirosis, various parasites, and equine encephalitis. As stated earlier, the
Coggins AGID test and immunoenzymatic tests (ELISA) are commonly used serological tests.
These tests are both accurate but can give false negatives during early periods of infection due to
low titer or, rarely, during the acute form viremia when the virus can potentially destroy
antibodies in the blood.xxiv It may be a few days to a few weeks post exposure before enough
antibodies are present to test positive for EIA.xxv Polymerase chain reaction (PCR) can be used to
detect viral EIA DNA and is most often used to confirm the aforementioned serological test.
PCR is also specifically used in the testing of newborns from infected mothers as the antibodies
for EIA from an animal’s mother may be present within the new born up to six months post
partum.xxvi
In order to prevent the spread of equine infectious anemia it is imperative that a proper
prevention strategy be adopted. There are currently no vaccines that are approved for protection
against EIA. Therefore, the best way to control the spread of disease is to reduce exposure to the
virus as much as possible. This can be achieved in a number of ways. A regulatory program
requiring that all equidae that are to be transported to a new location be tested for EIA and the
results mandated to be negative for the disease if transfer is to occur. This includes any
international importation or exportation of animals as well as intrastate and interstate travel.
Administration of either the ELISA or AGID serological tests should be used in this disease
screening process. These tests should be further applied to any animal of the equine family that is
exhibiting signs of EIA. Any suspect animal should be quarantined as a precautionary measure
against disease transmission. Upon positive test results, euthanasia of the infected animal is
highly recommended. If euthanasia is not desirable to the owner, certain quarantine measures
must be taken. The infected animal is to remain in its stall for the duration of its life for as long
as it lives. Screening of a proper size to prevent insects access to the infected equid should be
established surrounding the stall and kept in place at all times. Separate tack and bridle are to be
used and used for the EIA positive animal only. While screen mesh is used to prevent insect
transmission, it is also important to implement the entirety of the equine’s habitat with insect
control measures through any safe means possible. Applying proper insect control measures,
such as adequate sanitation and pesticide use, will help keep the primary vector for transmission
of this disease to a minimum and prevent transmissions from occurring on otherwise healthy
equine facilities. Among the most prevalent risks of accidental transmission is via improperly
disinfected instruments or equipment that is contaminated from use on an infected animal.
Veterinarians and all staff involved within the equine facility should implement proper hygiene
to prevent spread through infected organic material. It is important to note that the EIA virus is
highly susceptible to sunlight, boiling, and most common disinfectants.xxvii Therefore, equine
facilities with thorough sanitization programs can avoid the presence of this virus. Exceptions to
the transportation of EIA positive equids can be established if the infected animal is being
transported to its original home, to a slaughter facility, or to a research facility. Proper
precautions are to be implemented to prevent the spread of this disease and a permit declaring the
animal to be EIA positive should be present at all times. Permanent markings on the infected
equid should be established as well. These exceptions are approved with these federal regulations
only.xxviii Whenever a positive test result is received, a report should be filed and sent to a central
filing system within the government. This filing system would enable the United States to keep
track of the prevalence and significance of this disease. Once every year the incidents filed
should be reviewed and possible improvements should be discussed and made. Through the
application of the entirety of this prevention process, the same fundamentals of the hazard
analysis and critical control points program (HACCP) that is already implemented for a variety
of other diseases would be achieved. As HACCP has proven to be a successful means by which
to control the spread of diseases within the United States the program outlined in this paper
should prove to be effective.
Equine infectious anemia poses a significant threat to the equine industry. Through the
implementation of the aforementioned prevention plan, the EIA threat can be significantly
reduced and potentially eliminated as is its goal. In order for the aforementioned prevention plan
to be effective, there must be complete cooperation from all individuals involved with the equine
industry. Only through complete cooperation will biosecurity and biocontainment be acceptably
achieved within the United States and the threat of EIA reduced.
i
"National Economic Impact of the U.S. Horse Industry." Welcome to The American Horse Council. N.p., n.d. Web. 11 Dec. 2012.
ii
Ibid
Ibid
iv "Veterinary Division - Animal Health Programs." NCDA&CS. N.p., n.d. Web. 11 Dec. 2012.
iii
v
"Istituto Zooprofilattico "Giuseppe Caporale"" Istituto "G. Caporale" - Equine Infectious Anaemia_Description. N.p., n.d. Web.
11 Dec. 2012.
vi
"Veterinary Division - Animal Health Programs." NCDA&CS. N.p., n.d. Web. 11 Dec. 2012.
Ibid; Griel, Lester. “Regulatory Programs 2012.” Slides 25 and 26, VB SC 303, Pennsylvania State University, State College,
Pennsylvania.
viii "Istituto Zooprofilattico "Giuseppe Caporale"" Istituto "G. Caporale" - Equine Infectious Anaemia_Description. N.p., n.d. Web.
11 Dec. 2012.
ix "Merck Veterinary Manual." Merck Veterinary Manual. N.p., n.d. Web. 11 Dec. 2012.
vii
x
"Istituto Zooprofilattico "Giuseppe Caporale"" Istituto "G. Caporale" - Equine Infectious Anaemia_Description. N.p., n.d. Web.
11 Dec. 2012.
xi Ibid
xii Ibid
xiii Ibid
xiv "Equine Infectious Anemia." Equine Infectious Anemia. N.p., n.d. Web. 11 Dec. 2012.
xv
"Veterinary Division - Animal Health Programs." NCDA&CS. N.p., n.d. Web. 11 Dec. 2012.
Ibid
xvii "Istituto Zooprofilattico "Giuseppe Caporale"" Istituto "G. Caporale" - Equine Infectious Anaemia_Description. N.p., n.d. Web.
11 Dec. 2012.
xviii "Your Horse, Equine Infectious Anemia, and the Law." Equine Infectious Anemia. N.p., n.d. Web. 11 Dec. 2012.
xvi
xix
"Veterinary Division - Animal Health Programs." NCDA&CS. N.p., n.d. Web. 11 Dec. 2012.
"Istituto Zooprofilattico "Giuseppe Caporale"" Istituto "G. Caporale" - Equine Infectious Anaemia_Description. N.p., n.d. Web.
11 Dec. 2012.
xxi "Equine Infectious Anemia." Equine Infectious Anemia. N.p., n.d. Web. 11 Dec. 2012.
xxii "Istituto Zooprofilattico "Giuseppe Caporale"" Istituto "G. Caporale" - Equine Infectious Anaemia_Description. N.p., n.d. Web.
11 Dec. 2012.
xxiii "Veterinary Division - Animal Health Programs." NCDA&CS. N.p., n.d. Web. 11 Dec. 2012.
xxiv "Istituto Zooprofilattico "Giuseppe Caporale"" Istituto "G. Caporale" - Equine Infectious Anaemia_Description. N.p., n.d. Web.
11 Dec. 2012.
xxv "Merck Veterinary Manual." Merck Veterinary Manual. N.p., n.d. Web. 11 Dec. 2012.
xxvi "Istituto Zooprofilattico "Giuseppe Caporale"" Istituto "G. Caporale" - Equine Infectious Anaemia_Description. N.p., n.d. Web.
11 Dec. 2012.
xxvii "Veterinary Division - Animal Health Programs." NCDA&CS. N.p., n.d. Web. 11 Dec. 2012.
xxviii Ibid
xx
Works Cited
"Equine Infectious Anemia." Equine Infectious Anemia. N.p., n.d. Web. 11 Dec. 2012.
"Istituto Zooprofilattico "Giuseppe Caporale"" Istituto "G. Caporale" - Equine Infectious
Anaemia_Description. N.p., n.d. Web. 11 Dec. 2012.
"Merck Veterinary Manual." Merck Veterinary Manual. N.p., n.d. Web. 11 Dec. 2012.
"National Economic Impact of the U.S. Horse Industry." Welcome to The American Horse
Council. N.p., n.d. Web. 11 Dec. 2012.
"Veterinary Division - Animal Health Programs." NCDA&CS. N.p., n.d. Web. 11 Dec. 2012.
"Your Horse, Equine Infectious Anemia, and the Law." Equine Infectious Anemia. N.p., n.d.
Web. 11 Dec. 2012.