Investigations of a flock heavily infected with maedi-visna virus

Following the discovery that a flock of sheep in England was infected with the virus of maedi-virus, several seropositive sheep were brought to the Central Veterinary Laboratory and kept isolated and under observation for up to three years before being further examined at necropsy. Meanwhile, sheep in the infected flock which died or were culled were examined after death for evidence of the actual disease. At necropsy pulmonary disease was a common (although not always the sole) finding, the lesions being mostly chronic pasteurellosis and pulmonary adenomatosis. One of the 45 carcases examined showed classical lesions of advanced maedi. In four others, early or incipient lesions of maedi were found in otherwise normal lungs, while in three more, maedi was coincidental with the other pulmonary diseases. No clinical evidence to suggest maedi, other than emaciation, was seen in any of the sheep with lesions of the disease.