Necrotic enteritis in chickens: a paradigm of enteric infection by Clostridium perfringens type A.

Withdrawal of antimicrobial growth promoters and ionophore coccidiostats has been accompanied by a resurgence in incidence of necrotic enteritis (NE), a severe Clostridium perfringens-induced disease which some consider the most clinically dramatic bacterial enteric disease of poultry. Lesions, in jejunum and ileum, are focal-to-confluent, often with a tightly adhered pseudomembrane, and hemorrhage is uncommon. The key risk factor for development of NE is an intestinal environment that favors growth of the organism. Birds on high energy, protein-rich, wheat- or barley-based diets experience NE at a rate up to ten times greater than do birds on maize-based diets. Specific strains of type A cause NE, although only a few specific virulence attributes are known. The role of alpha toxin (CPA) has been called into question by the finding that an engineered CPA mutant retained full virulence in vivo, although the counterpoint to this is the finding that immunization with CPA toxoids provides substantial protection against NE. A recently described toxin, NetB, seems likely to be involved in pathogenesis of infection by most NE strains. Immunization with CPA, NetB, or other proteins, delivered by conventional means or vectored by recombinant attenuated Salmonella vectors may help the industry deal with NE. Future progress may be based in large part on genomic and proteomic analyses.