PATHOLOGICAL AND EPIDEMIOLOGIC ASPECTS OF THE COEXISTENCE OF MAEDI-VISNA AND SHEEP PULMONARY ADENOMATOSIS

Between 1982 and 1991, 159 sheep suffering from chronic respiratory disease were subjected to clinical, pathological, histopathological and serological examination. Maedi was diagnosed in 82 sheep and sheep pulmonary adenomatosis (SPA) in another 59. Forty-one of the latter (69.5 per cent) were seropositive for maedi-visna (MV) virus infection, but only six (10-2 per cent) showed concurrent lung lesions of maedi. Even disregarding the MV seronegative sheep and those younger than two years old, the rate of concurrent maedi lesions did not exceed 18 per cent. During a similar period, 5060 sheep from 161 flocks (86 of which also provided the 159 affected animals) were tested for antibodies to MV virus. The average seroprevalence of mv virus infection among flocks in which SPA was detected was 66.4 per cent, whereas in those in which SPA could not be demonstrated, and in those in which necropsies were not performed, the levels of mv virus infection were 55.1 per cent and 43.6 per cent, respectively. The effect Of SPA on the seroprevalence of mv virus infection was independent of other factors, such as breed of sheep or the size of the flocks. These results provide evidence that SPA plays a role in the spread of mv virus infection, although a synergistic effect of the simultaneous infection on the expression of concurrent lesions does not seem to occur.