Equine infectious anemia
Encyclopedia
Equine infectious anemia or equine infectious anaemia (EIA), also known by horsemen as swamp fever, is a horse disease caused by a retrovirus
and transmitted by bloodsucking insects. The virus is endemic in the Americas
, parts of Europe
, the Middle
and Far East
, Russia
, and South Africa
. The virus is a lentivirus
, like human immunodeficiency virus (HIV). Like HIV, EIA can be transmitted through blood, saliva, milk, and body secretions.
Transmission is primarily through biting flies, such as the horse-fly
and deer-fly
. The virus survives up to 4 hours in the carrier. Contaminated surgical equipment and recycled needles and syringe
s, and bit
s can transmit the disease. Mares can transmit the disease to their foals via the placenta
.
The risk of transmitting the disease is greatest when an infected horse is ill, as the blood levels of the virus are then highest.
(due to the breakdown of red blood cell
s), weakness, swelling of the lower abdomen and legs, weak pulse, and irregular heartbeat. The horse may die suddenly.
Subacute: A slower, less severe progression of the disease. Symptoms include recurrent fever, weight loss, an enlarged spleen
(felt during a rectal examination), anemia, and swelling of the lower chest, abdominal wall, penile sheath, scrotum, and legs.
Chronic
: Horse tires easily and is unsuitable for work. May have a recurrent fever and anemia, may relapse to the subacute or acute form even several years after the original attack.
There are currently no statistics available on mortality of EIA. No statistics are available of horses actually dying of acute forms. See also
A horse may also not appear to have any symptoms, yet still tests positive for EIA antibodies. This horse can still pass on the disease. According to most veterinarians, horses diagnosed EIA positive are usually not showing any sign of sickness or disease.
EIA may cause abortion in pregnant mares. This may occur at any time during the pregnancy if there is a relapse when the virus enters the blood. Most infected mares will abort, however some give birth to healthy foals. Foals are not necessarily infected.
Studies indicate that there are breeds with a tolerance to EIA.
Recent studies in Brazil on living wild horse
s have shown that in the Pantanal
, about 30% of domesticated and about 5.5% of the wild horses are chronically infected with EIA.
Reuse of syringes and needles is a risk factor for transfer of the disease. Currently in the United States, all horses that test positive must be reported to federal authorities by the testing laboratory. EIA-positive horses are infected for life.Options for the horse include sending the horse to a recognized research facility, branding the horse and quarantining it at least 200 yards from other horses for the rest of its life, and euthanizing the horse. Very few quarantine facilities exist which usually leads to the option of euthanizing the horse.The Florida Research Institute for Equine Nurturing, Development and Safety (a.k.a. F.R.I.E.N.D.S.) is one of the largest such quarantine facilities and is located in south Florida.
The horse industry and the veterinary industry strongly suggest that the risks posed by infected horses, even if they are not showing any clinical signs, are enough of a reason to impose such stringent rules. The precise impacts effect of the disease on the horse industry are unknown.
The Coggins test (agar immunodiffusion) is a sensitive diagnostic test for equine infectious anemia developed by Dr. Leroy Coggins in the 1970s.
Currently, the USA does not have an eradication program due to the low rate of incidence, however many states require a negative Coggins test for interstate travel. In addition, most horse shows and events require a negative Coggins test. Most countries require a negative test result before allowing an imported horse into the country.
It is recommended to verify that all the horses at a breeding farm and or boarding facility have a negative Coggins test before using their services. A Coggins test should be done on an annual basis. Tests every 6 months are recommended if there is increased traveling.
Retrovirus
A retrovirus is an RNA virus that is duplicated in a host cell using the reverse transcriptase enzyme to produce DNA from its RNA genome. The DNA is then incorporated into the host's genome by an integrase enzyme. The virus thereafter replicates as part of the host cell's DNA...
and transmitted by bloodsucking insects. The virus is endemic in the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
, parts of Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, the Middle
Middle East
The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...
and Far East
Far East
The Far East is an English term mostly describing East Asia and Southeast Asia, with South Asia sometimes also included for economic and cultural reasons.The term came into use in European geopolitical discourse in the 19th century,...
, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
, and South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. The virus is a lentivirus
Lentivirus
Lentivirus is a genus of slow viruses of the Retroviridae family, characterized by a long incubation period...
, like human immunodeficiency virus (HIV). Like HIV, EIA can be transmitted through blood, saliva, milk, and body secretions.
Transmission is primarily through biting flies, such as the horse-fly
Horse-fly
Insects in the order Diptera, family Tabanidae, are commonly called horse flies. Often considered pests for the bites that many inflict, they are among the world's largest true flies. They are known to be extremely noisy during flight. They are also important pollinators of flowers, especially in...
and deer-fly
Deer fly
Deer flies are flies in the genus Chrysops of the family Tabanidae that can be pests to cattle, horses, and humans. A distinguishing characteristic of a deer fly is patterned gold or green eyes....
. The virus survives up to 4 hours in the carrier. Contaminated surgical equipment and recycled needles and syringe
Syringe
A syringe is a simple pump consisting of a plunger that fits tightly in a tube. The plunger can be pulled and pushed along inside a cylindrical tube , allowing the syringe to take in and expel a liquid or gas through an orifice at the open end of the tube...
s, and bit
Bit (horse)
A bit is a type of horse tack used in equestrian activities, usually made of metal or a synthetic material, and is placed in the mouth of a horse or other equid and assists a rider in communicating with the animal. It rests on the bars of the mouth in an interdental region where there are no teeth...
s can transmit the disease. Mares can transmit the disease to their foals via the placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
.
The risk of transmitting the disease is greatest when an infected horse is ill, as the blood levels of the virus are then highest.
Stages
Acute: The acute form is a sudden onset of the disease at full-force. Symptoms include high fever, anemiaAnemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
(due to the breakdown of red blood cell
Red blood cell
Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...
s), weakness, swelling of the lower abdomen and legs, weak pulse, and irregular heartbeat. The horse may die suddenly.
Subacute: A slower, less severe progression of the disease. Symptoms include recurrent fever, weight loss, an enlarged spleen
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...
(felt during a rectal examination), anemia, and swelling of the lower chest, abdominal wall, penile sheath, scrotum, and legs.
Chronic
Chronic (medicine)
A chronic disease is a disease or other human health condition that is persistent or long-lasting in nature. The term chronic is usually applied when the course of the disease lasts for more than three months. Common chronic diseases include asthma, cancer, diabetes and HIV/AIDS.In medicine, the...
: Horse tires easily and is unsuitable for work. May have a recurrent fever and anemia, may relapse to the subacute or acute form even several years after the original attack.
There are currently no statistics available on mortality of EIA. No statistics are available of horses actually dying of acute forms. See also
A horse may also not appear to have any symptoms, yet still tests positive for EIA antibodies. This horse can still pass on the disease. According to most veterinarians, horses diagnosed EIA positive are usually not showing any sign of sickness or disease.
EIA may cause abortion in pregnant mares. This may occur at any time during the pregnancy if there is a relapse when the virus enters the blood. Most infected mares will abort, however some give birth to healthy foals. Foals are not necessarily infected.
Studies indicate that there are breeds with a tolerance to EIA.
Recent studies in Brazil on living wild horse
Wild Horse
The wild horse is a species of the genus Equus, which includes as subspecies the domesticated horse as well as the undomesticated Tarpan and Przewalski's Horse. The Tarpan became extinct in the 19th century, and Przewalski's Horse was saved from the brink of extinction and reintroduced...
s have shown that in the Pantanal
Pantanal
The Pantanal is a tropical wetland and one of the world's largest wetland of any kind. Most of it lies within the Brazilian state of Mato Grosso do Sul, but it extends into Mato Grosso and portions of Bolivia and Paraguay, sprawling over an area estimated at between and...
, about 30% of domesticated and about 5.5% of the wild horses are chronically infected with EIA.
Prevention and treatment
A vaccine is available, called "Chinese Live Attenuated EIA vaccine", developed in China and widely used there since 1983. Another attenuated live virus vaccine is in development in the United States.Reuse of syringes and needles is a risk factor for transfer of the disease. Currently in the United States, all horses that test positive must be reported to federal authorities by the testing laboratory. EIA-positive horses are infected for life.Options for the horse include sending the horse to a recognized research facility, branding the horse and quarantining it at least 200 yards from other horses for the rest of its life, and euthanizing the horse. Very few quarantine facilities exist which usually leads to the option of euthanizing the horse.The Florida Research Institute for Equine Nurturing, Development and Safety (a.k.a. F.R.I.E.N.D.S.) is one of the largest such quarantine facilities and is located in south Florida.
The horse industry and the veterinary industry strongly suggest that the risks posed by infected horses, even if they are not showing any clinical signs, are enough of a reason to impose such stringent rules. The precise impacts effect of the disease on the horse industry are unknown.
Diagnosis
Currently, the USA does not have an eradication program due to the low rate of incidence, however many states require a negative Coggins test for interstate travel. In addition, most horse shows and events require a negative Coggins test. Most countries require a negative test result before allowing an imported horse into the country.
It is recommended to verify that all the horses at a breeding farm and or boarding facility have a negative Coggins test before using their services. A Coggins test should be done on an annual basis. Tests every 6 months are recommended if there is increased traveling.