Ovine lentiviral infection (maedi/visna) in Morocco: a serologic and postmortem survey

In an attempt to estimate the importance of maedi/visna virus infection in Moroccan sheep and to assess the relationship, if any, between seroreactivity and pulmonary lesions, an abattoir-based serologic survey was undertaken over a period of 2 years. A total of 1000 blood samples and related lungs were collected from sheep of different breeds and ages slaughtered at three major municipal abattoirs in Morocco (Casablanca, Kénitra and Rabat). The agar gel immunodiffusion test showed that the seropositivity for all samples was 24.8%. At post-mortem examination, 107 out of the 248 (43.1%) sheep scored seropositive had gross lesions of maedi; typical microscopic lesions were observed in 125 (50.4%) seropositive sheep, including the 107 with gross lesions. Of the 752 seronegative animals, only 13 (1.7%) sheep had macroscopic maedi-like lesions. Seventeen (2.2%) of these seronegative cases, including those with gross lesions, had histologic pulmonary changes consistent with maedi. No other maedi/visna-associated lesions were found during this study; however, coexisting secondary bacterial bronchopneumonia was frequently encountered. The association between serologic and pathologic findings is reported and discussed.