EIAV—Equine infectious anemia virus

EIAV—Equine infectious anemia virus Equine Infectious Anemia Virus.

Equine infectious anemia virus (EIAV), the agent of equine infectious anemia, is a lentivirus that infects cells of the monocyte-macrophage system in horses (also ponies, donkeys, and mules). The virus is mechanically transmitted by biting flies, such as horseflies and deer flies. Less common routes of transmission include blood transfusions, contaminated medical equipment, and transplacentally. Disease may present in acute, subacute, and chronic forms and is potentially fatal. After an acute period of fever, depression, and thrombocytopenia that lasts 1 to 3 days, there is a prolonged period of recurrent fever, thrombocytopenia, and anemia. In most cases, clinical disease subsides within a year, and horses become lifelong carriers and reservoirs of EIAV.

EIAV causes anemia by both immune-mediated hemolysis and decreased erythropoiesis. Hemolysis is typically extravascular but may have an intravascular component during the acute phase. Decreased erythropoiesis may result from direct suppression of early-stage erythroid cells by the virus, as well as anemia of inflammation. Thrombocytopenia likely results from immune-mediated platelet destruction and suppressed platelet production.

Animals dying during hemolytic crises are pale with mucosal hemorrhages and dependent edema. The spleen and liver are enlarged, dark, and turgid, and they and other organs have superficial subcapsular hemorrhages. Petechiae are evident beneath the renal capsule and throughout the cortex and medulla. The bone marrow is dark red as a result of replacement of fat by hematopoietic tissue; the extent of replacement is an indication of the duration of the anemia.

The severity of microscopic lesions is dependent on the chronicity of the disease, and they are most significant in the spleen, liver, and bone marrow. As would be anticipated, microscopic findings of the spleen are predominantly influenced by the number and activity of macrophages, which is a reflection of the duration of the disease and the frequency of hemolytic episodes. Hemosiderin-laden macrophages persist for months to years; therefore large numbers are consistent with chronicity. Kupffer cell hyperplasia with hemosiderin stores and periportal infiltrates of lymphocytes are the most significant changes in the liver. Bone marrow histologic findings vary depending on the duration of the disease. In most animals the marrow is cellular because of the replacement of fat by intense, orderly erythropoiesis. Granulocytes are relatively less numerous, and plasma cells are increased. As in the spleen, hemosiderin-laden macrophages are present in large numbers in chronic cases. Emaciated animals with chronic disease have serous atrophy of fat (see E-Fig. 13-1).

Clinical findings with viremic episodes include fever, depression, icterus, petechial hemorrhages, lymph node enlargement, and dependent edema. Equine infectious anemia infection is diagnosed on the basis of the Coggins test, an agarose gel immunodiffusion test for the presence of the antibody against the virus.

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Equine Infectious Anemia Virus Retropepsin

József Tözsér, ... Stephen Oroszlan, in Handbook of Proteolytic Enzymes (Third Edition), 2013

Name and History

Equine infectious anemia virus (EIAV), causing an episodic wasting disease in horses colloquially known as swamp fever, is classified as a member of the lentivirus group of retroviruses and is closely related to the primate immunodeficiency viruses including human immunodeficiency virus type 1 (HIV-1) [1]. The location of a retropepsin gene in the EIAV genome was first suggested based on sequence homology [2]. Protein sequencing of its naturally occurring Gag [3] and Pol [4] substrates identified several cleavage sites, and their comparison with those of HIV-1 showed limited conservation and substantial variation in amino acid residues at the scissile bond and the neighboring sequence [4]. Active retropepsin was found in isolated EIAV capsids capable of in situ processing of the nucleocapsid protein [5]. An oligopeptide substrate representing the cleavage site between the matrix and capsid proteins of HIV-1 was found to be a good substrate of EIAV retropepsin, and its P1′ pipecolic acid-substituted derivative specifically inhibited the enzyme [6]. Expression of a plasmid containing the EIAV gag gene followed by in-frame insertion of the putative retropepsin coding sequence resulted in processing of the Gag polyprotein while out-of-frame insertion yielded intact Gag proteins [7]. The EIAV retropepsin is commonly referred to as EIAV protease (or proteinase).

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Immunoassay Applications in Veterinary Diagnostics

Thomas P. O'ConnorJr., ... Erwin Workman, in The Immunoassay Handbook (Fourth Edition), 2013

Equine Infectious Anemia Virus

Classification of organism/pathogenesis

Equine infectious anemia virus (EIAV) is an equine-specific retrovirus (lentivirus) that causes equine infectious anemia in horses around the world. The virus persists in the white blood cells of infected horses for life. Transmission occurs by transfer of blood cells from an infected horse, for example via insertion and withdrawal of contaminated hypodermic needles. The primary pathology of the disease is the immune-mediated destruction of red blood cells.

Test analyte

EIAV antibody.

Type of sample

Serum.

Assay technology

Both agar gel immunodiffusion (AGID) and ELISA technologies are being used to detect antibodies against p26 antigen, the major group-specific antigen found internally in the virus. For the ELISA format, both the p26 core and p45 envelope proteins may be represented within the test. The use of recombinant proteins makes these tests very specific for EIA, however, as the AGID is the prescribed test (World Organization for Animal Health), it is recommended that ELISA positives be retested by AGID. AGID and ELISA tests are available from IDEXX, Synbiotics, VMRD, and Centaur. The tests are formatted in either a competitive format (using anti-p26 as the solid phase) or in an antibody immunometric (sandwich) format (EIA antigens both coated on plates and conjugated to HRPO).

Frequency of use

Although the tests are used routinely in laboratories worldwide, sales to and use by laboratories is subject to satisfactory performance on periodic proficiency tests administered by local authorities.

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