Equine Infectious Anemia - contd.
Diagnosis is based on the affected horse's history, physical examination findings, and laboratory test results. The history may include inappetance, or loss of appetite, lethargy, and fever. Severely affected horses may have a history of high fever (105 - 106� F), depression, ventral edema, weight loss, ataxia, or incoordination, and epistaxis, or nosebleed. Additionally, physical examination findings could include poor body condition, mucosal petechiae, or pinpoint hemorrhage, or pale mucous membranes. Some affected horses may reveal no signs on physical examination.
Thrombocytopenia, or low platelet count, is the first laboratory abnormality detected in the acutely infected horse, and coincides with fever. Thrombocytopenia resolves along with resolution of clinical disease, but recurs with subsequent chronic disease cycles. Anemia, or abnormally reduced numbers of red blood cells, can occur shortly after infection, but generally is more severe during the chronic stage of the disease. Leukopenia, or low white blood cell count, lymphocytosis and monocytosis, or increased numbers of lymphocytes and monocytes, respectively, are observed in many infected horses. Hypergammaglobulinemia, or increased antibody protein levels, may be present. Elevations in liver enzymes may occur.
Definitive diagnosis is based on serologic testing. Both the agar gel immunodiffusion test, or AGID, also called the Coggins test, and competitive enzyme-linked immunosorbent assay, or C-ELISA, are approved by the United States Department of Agriculture for serologic diagnosis of EIA. Both tests detect serum antibodies to the EIAV group-specific core protein, p26. Most acutely infected horses produce detectable antibody within 45 days of infection. The Coggins test is the most widely used, and is 95 percent accurate in diagnosing EIAV infection. The C-ELISA may be more sensitive than the AGID, leading to possible false positive results. All horses testing positive with either test should be retested for confirmation.
