Contagious bovine pleuropneumonia (CBPP) caused by vaccine strain T1/44 of Mycoplasma mycoides subsp. mycoides SC

A study was carried out on four adult cattle to assess the pathogenicity of Mycoplasma mycoides subsp. mycoides SC strain T1/44, currently used as a vaccine for the control of contagious bovine pleuropneumonia (CBPP) in Namibia. Post mortem examination 9 weeks after endobronchial inoculation of the vaccine strain to three of the four animals revealed unilateral pleuropneumonic lesions, pleuritis and well-developed sequesters in two of the three inoculated animals and several small sequesters surrounded by pleuropneumonic lesions in the diaphragmatic and apical lobes in one animal. The fourth animal, which was not directly inoculated but was in close contact with the inoculated animals, revealed only an adhesion area of the lung to the ribcage. Serological examination carried out using the complement fixation test (CFT) detected positive titres in all three intubated animals and the indirect CBPP-LppQ-ELISA was positive for two of the three inoculated animals. The contact animal showed no seroconversion. M. mycoides subsp. mycoides SC was isolated from the sequesters of two of the inoculated animals. Isolation of mycoplasmas was not possible from the third inoculated animal due to heavy contamination of the samples by other bacteria, but the presence of M. mycoides subsp. mycoides SC could be evidenced by PCR from clinical samples. The identity of the T1/44 vaccine strain isolated from the sequesters of two animals was confirmed by T1/44-specific PCR analysis and by IS1296 typing using Southern blot. These results clearly show that inoculation of T1/44 vaccine via the endobronchial route can lead to CBPP.