Maedi-Visna (Ovine Progressive Pneumonia) Management Strategies

Abstract

Maedi-visna (ovine progressive pneumonia) is a lentivirus-induced lymphoid-proliferative disease syndrome of sheep characterized by chronic progressive pneumonia, encephalopathy, swollen joints causing lameness, and indurative lymphocytic mastitis. The primary mode of transmission is via the colostrum from infected ewes and to a lesser extent by management conditions that favor close proximity of sheep to one another. Seroprevalence to range from 19-97%, according to North American and European serological surveys of sheep.

Affected sheep typically show progressive weight loss, and dyspnea due to lymphocytic infiltration of the lungs. Neurological signs leading to paralysis, swollen joints causing lameness, and palpably hard, unproductive udders or "hard bag" may occur concurrently or separately in affected sheep. Once infected with the ovine lentivirus, antibodies are produced to the virus that do not confer resistance to the disease, which is ultimately fatal. Definitive diagnosis of maedi-visna can be made from the clinical signs, histopathology, and AGID and/or the ELISA tests that detect the presence of circulating antibody. The ELISA test has greater sensitivity and specificity than the AGID test.

Maedi-visna is best managed by eradicating the virus. Eradication strategies include removing new born lambs at birth from their infected dams before they can suckle colostrum, and then raising them in isolation. Serological testing of all sheep over three years of age and culling infected animals and their progeny will reduce seroprevalence in the flock. Repeated annual testing is required until the herd has at least two negative herd tests.