Equine infectious anemia or equine infectious anaemia (EIA), also known by horsemen as swamp fever, is a horse disease caused by a

retrovirus A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. Once inside the host cell's cytoplasm, the virus uses its own reverse transcriptase ...

(''Equine infectious anemia virus'') and transmitted by bloodsucking insects. The virus (''EIAV'') is endemic in the

Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. Along with th ...

, parts of

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

, the Middle and

Far East The ''Far East'' was a European term to refer to the geographical regions that includes East and Southeast Asia as well as the Russian Far East to a lesser extent. South Asia is sometimes also included for economic and cultural reasons. The ter ...

Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

, and

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

. The virus is a

lentivirus ''Lentivirus'' is a genus of retroviruses that cause chronic and deadly diseases characterized by long incubation periods, in humans and other mammalian species. The genus includes the human immunodeficiency virus (HIV), which causes AIDS. Lent ...

, like

human immunodeficiency virus The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause AIDS, acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the ...

(HIV). Like HIV, EIA can be transmitted through blood, milk, and body secretions. Transmission is primarily through biting flies, such as the

horse-fly Horse-flies or horseflies are true Fly, flies in the family Tabanidae in the insect Order (biology), order Diptera. They are often large and agile in flight, and only the female horseflies bite animals, including humans, to hematophagy, obtai ...

and deer-fly. The virus survives up to 4 hours in the

vector Vector most often refers to: *Euclidean vector, a quantity with a magnitude and a direction *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematic ...

. Contaminated surgical equipment and recycled needles and

syringe A syringe is a simple reciprocating pump consisting of a plunger (though in modern syringes, it is actually a piston) that fits tightly within a cylindrical tube called a barrel. The plunger can be linearly pulled and pushed along the inside ...

s, and

bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...

s can transmit the disease. Mares can transmit the disease to their foals via the

placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...

. 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 Acute may refer to: Science and technology * Acute angle ** Acute triangle ** Acute, a leaf shape in the glossary of leaf morphology * Acute (medicine), a disease that it is of short duration and of recent onset. ** Acute toxicity, the adverse eff ...

: The acute form is a sudden onset of the disease at full-force. Symptoms include high fever,

anemia Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, th ...

(due to the breakdown of

red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

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 The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .

(felt during a rectal examination), anemia, and swelling of the lower chest, abdominal wall,

penile sheath Almost all mammal penises have foreskins or prepuce, although in non-human cases the foreskin is usually a sheath (sometimes called the ''preputial sheath'', ''praeputium'' or ''penile sheath'') into which the whole penis is retracted. In koalas, ...

, scrotum, and legs. Chronic: The horse tires easily and is unsuitable for work. The horse may have a recurrent fever and anemia, and may relapse to the subacute or acute form even several years after the original attack. A horse may also not appear to have any symptoms, yet still tests positive for EIA antibodies. Such a horse can still pass on the disease. According to most veterinarians, horses diagnosed EIA positive usually do not show 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 The wild horse (''Equus ferus'') is a species of the genus ''Equus'', which includes as subspecies the modern domesticated horse (''Equus ferus caballus'') as well as the endangered Przewalski's horse (''Equus ferus przewalskii''). The Europea ...

s have shown that in the

Pantanal The Pantanal () is a natural region encompassing the world's largest tropical wetland area, and the world's largest flooded grasslands. It is located mostly within the Brazilian state of Mato Grosso do Sul, but it extends into Mato Grosso and p ...

, 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 of the disease on the horse industry are unknown.

Diagnosis

The Coggins test (agar immunodiffusion) is a sensitive diagnostic test for equine infectious anemia developed by Dr.

Leroy Coggins Leroy Coggins (1932–2013) was a virologist who developed tests for African swine fever and equine infectious anemia. The latter is now known as the Coggins Test and a "negative Coggins" is commonly required when horses are sold or transported ...

in the 1970s. Currently, the US 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. Horse owners should verify that all the horses at a breeding farm and or boarding facility have a negative Coggins test before using the services of the facility. A Coggins test should be done on an annual basis. Tests every 6 months are recommended if there is increased traveling.

References

External links

* {{Authority control Animal viral diseases Horse diseases Lentiviruses