Pathological and immunological characteristics of ewes experimentally infected with Mycoplasma mycoides subsp. mycoides SC strains isolated from cattle and sheep

Abstract The pathological features of experimental infection with Mycoplasma mycoides subsp. mycoides small colony ( Mmm SC) isolated from cattle (CBPP strain) and sheep (mastitis strain) were investigated in 16 out of 36 ewes using an intratracheal–endobronchial route of inoculation. Animals kept in-contact with infected animals, as well as those of a control group, were also studied. The immune response to two strains was also assessed. Complement fixation test (CFT) and immunoblotting (IBT) used for contagious bovine pleuropneumonia (CBPP) diagnosis, were performed on serum obtained from weekly blood samples. Only one ewe inoculated twice with the bovine isolate showed hyperplasia of the germinal centres in the lymph nodes and mucosa-associated lymphoid tissue in the lung. This ewe also exhibited a CFT titre of 1:160 simultaneously showing specific antibodies to 110, 98, 95, 62 and 48 kDa immunogenic bands. Interstitial pneumonia and thickening of pulmonary septa were observed in 10 inoculated and 6 in-contact ewes. Statistical analysis of the incidence of interstitial pneumonia indicated that the lesion was related to mycoplasma infection. The strongest immune response occurred at day 77 post-exposure to immunogenic antigens with molecular weights of 110, 98, 95, 62, 60 and 48 kDa in ewes from both inoculated groups. Taking into consideration the inoculum dose rate, ewes receiving the bovine isolate produced an earlier and more pronounced immune response than those receiving the ovine isolate. A mild response was seen in three ewes in-contact first and then inoculated with the ovine isolate. In spite of a relatively weak serologic reaction detected, the results suggested the possibility of contact transmission among animals.