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Animal Disease Factsheets
www.cfsph.iastate.edu
This factsheet is made available by:
The Center for Food
Security and Public Health
Iowa State University
College of Veterinary Medicine
The mission of the CFSPH is to increase national and international
preparedness for accidental or intentional introduction of disease
agents that threaten food production or public health.
Other resources at www.cfsph.iastate.edu
• Handbook for Zoonotic Diseases of Companion Animals
• Emerging and Exotic Diseases of Animals Book
• Avian Influenza Resources
• Wall Charts and Handouts
Published in IVIS with the permission of the Center for Food
Security & Public Health, Iowa State University.
Equine
Infectious Anemia
Swamp Fever, Mountain Fever,
Slow Fever, Equine Malarial
Fever, Coggins Disease
Last Updated: Aug. 2, 2005
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Importance
Equine infectious anemia (EIA) is a retroviral infection of horses that results in
acute symptoms in some animals, and chronic fevers, anemia, edema, and cachexia in
others. All infected horses, including those that are asymptomatic, become carriers and
are infectious for life. Infected animals must either be destroyed or remain permanently
isolated from other horses to prevent transmission.
Etiology
Equine infectious anemia is caused by equine infectious anemia virus (EIAV), a
lentivirus (family Retroviridae) related to the human immunodeficiency virus. EIAV
becomes incorporated into leukocyte DNA in both symptomatic and asymptomatic animals. This virus displays significant antigenic drift.
Species affected
Equine infectious anemia virus affects members of the Equidae.
Geographic distribution
Equine infectious anemia has been found worldwide. This virus exists in the United
States.
Transmission
Equine infectious anemia is transmitted mechanically on the mouthparts of biting
flies in the genus Stomoxys (horse flies and deer flies). Transmission is more common
in the summer and in humid, swampy regions. EIA can also be spread on contaminated
needles or surgical instruments, and passed from a mare to her foal in utero.
In infected horses, EIAV persists in the white blood cells for life. Horses with inapparent infections are less likely to transmit the disease than horses with chronic symptoms; after visiting an asymptomatic carrier, only one out of every 6 million flies is likely
to become a vector.
Incubation period
The incubation period is usually one to three weeks, but may be as long as three
months.
Clinical signs
Institute for International
Cooperation in Animal Biologics
An OIE Collaborating Center
Iowa State University
College of Veterinary Medicine
The clinical signs of acute EIA are often nonspecific. In some acute cases, the only
symptom noted is a fever which, in mild cases, can last less than 24 hours. Other clinical
signs can include weakness, severe anemia, jaundice, tachypnea, petechiae on the mucus
membranes, and blood–stained feces. Occasionally, death occurs during the acute infection. After the initial bout, most horses become asymptomatic carriers. Some develop
recurring symptoms that vary from mild illness and failure to thrive to fever, depression, petechial hemorrhages on the mucus membranes, weight loss, anemia, dependent
edema, and sometimes death. Inapparent infections may become symptomatic during
concurrent illnesses, severe stress, or hard work.
Post mortem lesions
Center for Food
Security and Public Health
College of Veterinary Medicine
Iowa State University
Ames, Iowa 50011
Phone: (515) 294–7189
FAX: (515) 294–8259
E–mail: [email protected]
Web: http://www.cfsph.iastate.edu
EIA_A0805
In acutely infected animals, the spleen and its associated lymph nodes are enlarged.
In chronic infections, there may be emaciation, splenomegaly, pale mucous membranes,
and enlarged abdominal lymph nodes. Edema is common, particularly in the limbs and
along the ventral abdominal wall. Intravascular clotting and emboli are frequently seen
in advanced cases. Some animals may have proliferative glomerulonephritis. Reticuloendothelial cell proliferation in multiple organs is common.
Morbidity and Mortality
Morbidity varies with the geographic region. Morbidity is difficult to predict, as
virus transmission depends on the number of flies, their habits, the number of times a fly
bites the same or other horses, the density of the horse population, the amount of virus
© 2003
Animal Disease Factsheets, The Center for Food Security & Public Health
Iowa State University, Ames, IA, USA.
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Published in IVIS with the permission of the Center for Food
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Equine Infectious Anemia
in the blood of the infected horse, and the quantity of blood
transferred. Infection rates as high as 70% have been seen on
farms where the disease has been endemic for many years.
The mortality rate can be as high as 80% during the acute
stage of experimental infections, if the dose of virus is high.
However, deaths are uncommon in most natural infections.
No vaccine or treatment is available.
Diagnosis
Recommended actions if
equine infectious anemia is suspected
Notification of authorities
Equine infectious anemia is a reportable disease in many
states. Each state should be checked for specific regulations.
Federal: Area Veterinarians in Charge (AVICS) http://www.
aphis.usda.gov/vs/area_offices.htm
State vets: http://www.aphis.usda.gov/vs/sregs/official.
html
Clinical
Quarantine and Disinfection
Equine infectious anemia should be suspected in individual horses with weight loss and intermittent fever. It
should also be considered when several horses experience
fever, anemia, edema, progressive weakness, or weight loss,
particularly when new animals have been introduced into the
herd or a member of the herd has died.
The differential diagnosis includes other febrile illnesses, including anthrax, influenza, and equine encephalitis.
Infected horses must be permanently isolated from other horses or euthanized. A reactor is usually marked with a
brand, freezemarking, or a lip tattoo, and cannot be transported between states (except to its home farm, a slaughterhouse, or a diagnostic or research facility, under quarantine
conditions). Foals born to infected mares should be isolated
from other horses until maternal antibody disappears and the
foal is determined to be free of infection.
Enveloped viruses such as EIAV can be destroyed by
most common disinfectants.
Laboratory tests
Public health
Differential diagnosis
Equine infectious anemia is confirmed by serology. The
agar gel immunodiffusion (Coggins) test is the “gold standard” used for confirmation of the disease. Enzyme–linked
immunosorbent (ELISA) assays are also available. Positive
results on ELISA are confirmed with the Coggins test, as
false positives are sometimes seen. Antibodies may not be
detected early in the disease.
Negative serologic tests are necessary for interstate
movement of horses. State regulations vary, but many states
require periodic tests, a single mandatory test, or tests before
participation in organized activities.
Virus isolation is not usually required for a diagnosis,
but it is occasionally done. The virus can be isolated by
inoculating blood from a suspected carrier onto leukocyte
cultures. Virus identity is confirmed by ELISA or immunofluorescence tests.
If the status of a horse cannot be determined by other
methods, blood may be inoculated into a susceptible horse.
Antibody status and clinical signs in the test animal should
be monitored for at least 45 days.
Samples to collect
Serum should be collected for serology. Occasionally,
unclotted blood may be collected for virus isolation or inoculation into a test animal.
Last Updated: Aug. 2005
There is no evidence that equine infectious anemia is a
threat to humans.
For More Information
World Organization for Animal Health (OIE)
http://www.oie.int
OIE Manual of Standards
http://www.oie.int/eng/normes/mmanual/a_summry.
htm
OIE International Animal Health Code
http://www.oie.int/eng/normes/mcode/A_summry.
htm
Animal Health Australia. The National
Animal Health Information System (NAHIS)
http://www.aahc.com.au/nahis/disease/dislist.asp
Equine Infectious Anemia. American
Association for Horsemanship Safety.
http://tarlton.law.utexas.edu/dawson/eia/eia.htm
References
“Code of Federal Regulations Title 9, Chapter I, Subchapter C. Interstate Transportation of Animals (including
poultry) and Animal Products. Part 75 – Communicable Diseases In Horses, Asses, Ponies, Mules, and
Zebras. Equine Infectious Anemia (Swamp Fever).”
. 26 Sept 2001 <http://tarlton.law.utexas.edu/dawson/eia/
us_eia.htm>.
© 2003
Animal Disease Factsheets, The Center for Food Security & Public Health
Iowa State University, Ames, IA, USA.
page of 3
Published in IVIS with the permission of the Center for Food
Security & Public Health, Iowa State University.
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www.ivis.org
Equine Infectious Anemia
“Equine Infectious Anemia.” American Association for
Horsemanship Safety. 26 Sept 2001 < http://tarlton.
law.utexas.edu/dawson/eia/eia.htm>.
«Equine Infectious Anemia.» In Manual of Standards for
Diagnostic Tests and Vaccines. Paris: World Organization for Animal Health, 2000, pp. 542–545.
“Equine Infectious Anemia.” In The Merck Veterinary
Manual, 8th ed. Edited by S.E. Aiello and A. Mays.
Whitehouse Station, NJ: Merck and Co., 1998, pp.
499–500.
“Equine Infectious Anemia.” In Veterinary Virology. Edited by F.A. Murphy, E.P.J. Gibbs, M.C. Horzinek, and
M.J. Studdert. San Diego, CA: Academic Press, 1999,
pp. 386–7.
“Equine Infectious Anemia.” Oct. 1996 USDA:APHIS:
VS, CEAH, National Animal Health Monitoring System. 26 Sept 2001 <http://www.aphis.usda.gov:80/oa/
pubs/fseia.html>
Last Updated: Aug. 2005
© 2003
Animal Disease Factsheets, The Center for Food Security & Public Health
Iowa State University, Ames, IA, USA.
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