Assessment of a PPD tuberculin produced from the BCG strain of Mycobacterium bovis for use in cattle

The possibility of using BCG — a Mycobacterium bovis strain of attenuated virulence for PPD production instead of a virulent strain of M. bovis has been considered to avoid the biological risks involved in the procedure. The potency and specificity of a PPD tuberculin prepared from BCG was compared in guinea pigs with that of PPD produced from strain AN5 (two batches), a virulent strain of M. bovis: the European Communities Standard (ECS), and a reference batch prepared at the Pan American Zoonoses Center (CPZ). The potency of the BCG-PPD was also assessed in cows naturally infected with M. bovis in comparison with the other two PPD and a third (WS) produced at the Central Veterinary Laboratory, Weybridge, United Kingdom. Finally, the antigenic value of BCG-PPD was compared with that of CPZ and ECS in an ELISA against sera from tuberculous and healthy cattle. In the above assays, BCG-PPD showed a lower sensitivity and specificity than PPD produced from virulent M. bovis. Therefore its use either for tuberculin testing of cattle or as antigen in the ELISA test for detecting bovine IgG anti-M. bovis antibodies would not seem advisable.