Vaccine-based control of necrotic enteritis of broiler chickens
A vaccine for necrotic enteritis (NE) in chickens would be valuable because antimicrobial use is under scrutiny. The objective was to develop a vaccine against NE in chickens. The first experiment determined whether subculture of 'C. perfringens ' led to attenuation by loss of a plasmid encoding the beta2 toxin gene, 'cpb2'. Isolates were tested for the ability to cause NE. Four of six parental strains were found to be virulent, and three of these strains were attenuated after subculture despite the presence of plasmid-encoded Cpb2. The second experiment tested attenuated strains as vaccine candidates. Two virulent parental isolates protected chickens from NE, but avirulent isolates did not. Two of four phenotypically alpha-toxin-negative (Cpa- ) isolates, which were essentially attenuated for virulence, also protected chickens from NE. In conclusion, it was shown to be possible to vaccinate chickens successfully against NE with Cpa- isolates and that attenuation was independent of plasmid-encoded Cpb2.