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Equine Infectious Anemia (aka EIA, Swamp Fever)

posted by Horse Owner Today    |   September 20, 2011 10:40

The disease

Equine infectious anemia (EIA), also commonly referred to as swamp fever or Coggins disease, is a viral disease of horses and other equidae that affects the immune system. It is transmitted by blood, mainly via blood-sucking insects, and by needles contaminated with blood containing the virus, or through breeding. The EIA virus can only reproduce in living cells, and in this way spreads throughout the animal. All infected horses carry the virus for life. The fact that the virus lives within the cell is the reason treatment and vaccination are ineffective.

In general, there are three forms of EIA in which the virus can be detected by the presence of antibodies produced by the horse in response to the EIA infection. In EIA's acute form, the virus actively multiplies and attacks the immune system and other body organs. Some of these horses may die suddenly, others may appear constantly and severely ill and harbor heavy concentrations of the virus in their blood. Horses afflicted by the chronic form of the disease may also contain high concentrations of the virus, but they tend to alternate between periods of appearing healthy and the disease state seen in the acute form. Some of these animals will debilitate over time, and present poor body condition. Acute and chronically infected horses always pose a high risk of infection to EIA-free horses because they have a high concentration of virus in their blood. The third form of EIA involves unapparent carriers. These are seemingly healthy horses that also carry the virus, but in a low or undetectable concentration in the blood. Inapparent carriers may never become acute or infectious; however, stress and other diseases or treatments can activate the acute form resulting in a high concentration of virus in the bloodstream. This third form of the disease is often the source of debate about the meaning of the Coggins test and the fate of the unapparent carriers among horse owners who are not well-informed about the disease.

The clinical symptoms of EIA depend on the severity of infection and vary from horse to horse. They can include one or more of the following: fever, depression, decreased appetite, fatigue or reduced stamina, rapid breathing, sweating, weight loss, bloody or watery eye discharge, swelling of legs, lower chest and abdomen, general weakness, wobbly gait, pale or yellowish mucous membranes, signs of abdominal pain, and abortion in pregnant mares.

The origin and evolution of the EIA control program

EIA has been recognized in Canada since 1881, originally as swamp fever. Initial efforts to control this disease based on the elimination of clinically ill horses were largely unsuccessful because infected but unapparent carriers perpetuated the disease within the horse population and served as a continuous source of infection for disease-free horses. In 1970, Dr. Leroy Coggins developed a diagnostic test for EIA using an agar-gel immunodiffusion (AGID) reaction. The Coggins' test is consistently reliable in detecting the presence of antibodies regardless of whether the infection is acute, chronic or unapparent. The test's reliability and the identification of unapparent carriers paved the way for implementation of more successful EIA control programs.

In 1971, EIA was made a reportable disease in Canada, and the first EIA program was introduced in 1972. Agriculture Canada offered the Coggins test to Canadian horse owners and voluntary testing was performed by accredited veterinarians. The government was only involved in trace-out investigations and testing after a reactor was reported. EIA reactors were either permanently quarantined or destroyed. There was no compensation paid for any destroyed horses during the first seven years of the program, but in 1978 the federal government introduced the compensation payment of $200 to owners whose horses were euthanised. In 1989, Agriculture Canada began to accredit private laboratories to perform the Coggins test although all atypical or positive results were confirmed in a federal laboratory before any quarantine and investigation activities were implemented.

From 1972 to 1993, of the approximately 1.8 million horses tested, some 14,000 were confirmed positive for EIA. Although some owners chose permanent quarantine for their animals, the majority of horses were destroyed. During the same time period, the rate of infection among horses tested dropped from 2.9% to 0.39%, indicating that the program reduced the number of infected horses and was successful in controlling the spread of the disease in all but some remote and high risk areas.

In 1994, the government reprioritized its activities and reduced its involvement in the program by modifying the EIA control policy. EIA remained a reportable disease and testing procedures and requirements did not change; however, Agriculture Canada notified the owners and "contact animal" owners instead of investigating reactors and testing positive animals. Horses in contact with reactors were not quarantined and their testing was conducted at the owner's expense by Canadian Food Inspection Agency (CFIA)-accredited veterinarians. Owners required a federal licence to remove infected animals from a premises. At this time the government also discontinued ordering the destruction of infected horses and the payment of compensation. Between 1994 and 1998, approximately 337,000 horses were tested and close to 550 reactors were either voluntarily destroyed or permanently isolated. During that period, the rate of infection among tested horses increased from 0.39% in 1993 to 0.66% as recorded in 1999.

The current EIA control program

In April 1998, the newly created CFIA was approached by the equine industry to modify the EIA program. EIA does not pose a risk to food safety or human health; however, the CFIA agreed that unless EIA was controlled there could be devastating effects on the Canadian horse industry including those related to international trade. Consequently the CFIA agreed to participate in the control of EIA providing the new program was industry-driven and self-funded.

This current program consists of two components. Under the first component, horse owners voluntarily pay to have their horses tested when they are identified by the industry (i.e. movement into shows, point of sale, etc.). Testing is conducted by private veterinary practitioners and EIA private laboratories accredited by CFIA for that function. The second component of the program is the mandatory response, for which the CFIA is responsible. Each time an EIA positive horse is discovered, it must be reported to the CFIA and disease control measures are implemented. The premises on which a reactor is discovered is declared an infected place and all susceptible animals must test negative to be allowed to move off the property. Horses in contact with the reactor within 30 days of the sampling date are also tested. All EIA test-positive horses are retested and reactors with clinical signs are ordered destroyed. Owners of horses that are confirmed positive for EIA without clinical signs must choose whether to either keep the horse in a permanent quarantine or have it destroyed. In the later case, the CFIA orders the horse destroyed and pays compensation. The government's part of the program is delivered at no charge to owners.

When the program was introduced in 1998, the maximum amounts payable were set at $500 and $1000 for grade and pure-bred horses respectively. To further promote the program and encourage testing, compensation has increased to a maximum amount payable of $2000 per horse.

Accredited laboratories charge owners $2 for each animal tested to offset the cost of the CFIA's mandatory response. While this amount may, in some years, cover the cost of compensation, it does not cover CFIA's cost in terms of manpower and operating cost. This is provided as a service to the industry.

The CFIA's position on EIA control program

The CFIA has not imposed the EIA program on horse owners, but has responded to a request from the industry to administer a program that the majority of horse owners support. Participation in the program is voluntary and all elements of the program have been developed in conjunction with the industry. The program is based on internationally recognized disease control standards, current knowledge of the disease, and diagnostic methods. As there is no effective treatment for EIA and no vaccine to prevent it, the disease can be successfully controlled by testing and the elimination of reactors including unapparent ones. The Coggins test is an integral part of the CFIA control program.

EIA does not pose a food safety risk and is not a public health concern, therefore the CFIA's involvement is based on the furtherance of animal health in Canada.

for more information:  www.inspection.gc.ca