Equine Infectious Anemia

Test codes:
S0064 - Ultrasensitive qualitative detection of equine infectious anemia proviral DNA by real time polymerase chain reaction

Equine infectious anemia (EIA), also known as Swamp Fever, is a viral disease known to occur in all members of equidae, including horses, mules and donkeys. Equine infectious anemia virus (EIAV) is a member of the genus Lentivirus of the family Retroviridae. EIAV is unique among the lentiviruses in that the initial acute febrile response and associated viremia are followed by recurrent cycles of the disease and, finally, a prolonged asymptomatic period.

Acute cases experience fever and hemorrhaging 7-30 days post infection. Very few horses with this initial fever are detected by owners. Chronic infection is marked by episodes of fever, weight loss, depression, progressive weakness, anemia and edema. These signs occur every two weeks in recurring cycles.

Other symptoms that may occur during the course of the disease include loss of appetite, frequent urination, diarrhea, weakness, paralysis of the hindquarters, paleness of the mucous membranes, yellowish discoloration of the conjunctiva, small pinpoint hemorrhages beneath the tongue, rapid breathing and accelerated pulse. Pregnant mares may abort.

The onset of these signs is often associated with stresses such as hard work, hot weather, racing, pregnancy or use of steroid drugs. Some animals show no clinical signs associated with the infection and may go undetected. These apparently healthy carriers harboring the virus are a constant reservoir of infection.

There is currently no effective vaccine to prevent EIAV infection. Routine serological testing and removal of seropositive reactors limits the spread of this disease. However, the utility of serological tests depends on the length of time it takes for an animal to mount an immune response and on the test’s sensitivity and sensitivity of antibody detection. Currently, the agar gel immunodiffusion assay (the Coggins test) is widely accepted and used for serodetection of EIAV group specific antigen p26. Competitive enzyme-linked immunosorbent assay (c-ELISA) and synthetic antigen ELISA (SA-ELISA) have also been used for the serological detection of EIA specific antibodies. A fluorescent polarization-based diagnostic assay for detection of EIAV antibodies has also been reported ( Tencza et al., 2000). Besides serological assays, virus isolation can be used but it is not practical because it is time consuming, laborious and requires specialized technical skills to maintain primary horse macrophage cultures for the replication of pathogenic strains of EIAV. The high cost and slowness of virus isolation make it unsuitable for routine monitoring.

Detection of EIAV proviral DNA in blood cells by PCR has been shown to be more sensitive and specific than serological assays not only in identifying subclinical EIAV-infected horses, but also recently infected horses still in the process of mounting an immune response (Spyrou, et al., 2003).

Utilities:

• Confirm the disease causing agent
• Shorten the time required to confirm a clinical diagnosis of EIA virus infection.
• Ensure that horse populations are free of EIA virus
• Early prevention of spread of the virus
• Minimize personnel exposure to the virus
• Safety monitoring of biological products that derive from horses

References:
Spyrou, V., Papanastassopoulou, M., Psychas, V., Billinis, C.H, Koumbati, M., Vlemmas, J. and Koptopoulos, G. (2003). Equine infectious anemia in mules: virus isolation and pathogenicity studies. Vet Microbiol. 95:49-59.
Tencza, S.B., Islam, K.R., Kalia, V., Nasir, M.S., Jolley, M.E. and Montelaro, R.C. (2000). Development of a fluorescence polarization-based diagnostic assay for equine infectious anemia virus. J. Clin. Microbiol. 38:1854–1859.

Specimen requirements: 1 ml whole blood in EDTA (purple top) or ACD (yellow top) tube, or 1 ml tissue, shipped overnight at room temperature; or 1 ml frozen tissue, shipped frozen.

For specimen types other than those listed here, please call to confirm specimen acceptability and shipping instructions.

For all specimen types, if there will be a delay in shipping, or during very warm weather, refrigerate specimens until shipped and ship with a cold pack unless more stringent shipping requirements are specified. Frozen specimens should be shipped so as to remain frozen in transit. See shipping instructions for more information.

Turnaround time: 2 business days

Methodology: Qualitative real time PCR

Normal range: Nondetected