Type C and C/D toxigenic Clostridium botulinum is not normally present in the intestine of healthy broilers

Toxigenic Clostridium botulinum spores are widely distributed in wetland environments and are frequently recovered from healthy wild birds, where ingestion of toxic maggots from carcasses is considered a major initiating factor for botulism outbreaks. Toxic carcasses can perpetuate an existing outbreak also in poultry, but their importance as an initiating factor for poultry botulism is less clear. Although toxigenic C. botulinum can be recovered from healthy broilers during outbreaks, there are almost no data on the prevalence in healthy broiler flocks (and, by extension, carcasses) and their environment. To test the hypothesis that toxigenic C. botulinum is frequently present in healthy broilers, we examined 100 healthy broiler flocks and environmental samples from 30 broiler houses 3 to 4 years after an epidemic of botulism in the broiler population. None of the 100 flocks yielded type C or C/D botulinum toxin genes using real time PCR whereas a flock house that had remained empty since the most recent outbreak yielded type C (or C/D) toxin genes. The absence of toxigenic C. botulinum in all examined flocks indicates that botulism is a sporadic and exogenously acquired event in this broiler population and unlikely to mirror the epidemiology in wild birds.