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By Dr. Tahseen Aziz, Rollins Animal Disease Diagnostic Laboratory, Raleigh, NC, USA and Dr. H. John Barnes, College of Veterinary Medicine, NC State University, Raleigh, NC, USA
Necrotic enteritis (NE) is an enteric bacterial disease of chickens, turkeys, and a few other avian species caused by Clostridium perfringens. The disease is characterised by damage to the intestinal mucosa by toxins produced by the causative bacteria. It is worldwide in distribution and causes considerable financial losses to broiler producers due to mortality and, in its milder subclinical form, poor growth and feed utilisation. In commercially raised broiler chickens, clinical disease usually occurs between 2 and 5 weeks of age.The causative bacterium
Necrotic enteritis is caused by C. perfringens, a gram-positive, rod-shaped, spore-forming, anaerobic bacterium. C. perfringens is ubiquitous, found in used litter, soil, and intestinal tracts of healthy birds. Feed and litter contaminated with large numbers of C. perfringens have been convincingly implicated as a source of infection. The disease occurs when C. perfringens overgrows in the intestinal tract and produces potent toxins that severely damage the intestinal mucosa. Toxins absorbed from the intestinal tract produce a toxemia (toxin in blood), which is responsible for death of the bird. Thus, NE is a type of “enterotoxemia”.
Necrotic enteritis is caused by C. perfringens, a gram-positive, rod-shaped, spore-forming, anaerobic bacterium. C. perfringens is ubiquitous, found in used litter, soil, and intestinal tracts of healthy birds. Feed and litter contaminated with large numbers of C. perfringens have been convincingly implicated as a source of infection. The disease occurs when C. perfringens overgrows in the intestinal tract and produces potent toxins that severely damage the intestinal mucosa. Toxins absorbed from the intestinal tract produce a toxemia (toxin in blood), which is responsible for death of the bird. Thus, NE is a type of “enterotoxemia”.
C. perfringens is divided into five toxinotypes (A, B, C, D, and E) based on four major toxins (alpha, beta, epsilon, and iota). The majority of isolates from NE cases are type A, with a few cases caused by type C. Alpha toxin produced by types A and C, beta toxin produced by type C, and possibly other toxins produced by the organism are responsible for the damage to the intestine, enterotoxemia, and death of the bird.
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Pathogenesis is partly unclear
The pathogenesis of NE is not fully understood. There is convincing evidence that C. perfringens strains vary in virulence and that NE is caused by certain strains of the organism (“NE strains”). Why these are capable of inducing NE remains unknown. Several studies have shown that in a NE outbreak, a single virulent strain displaces the genetically heterogeneous enteric population of C. perfringens in the intestinal tract of the chicken. However, it is not clear what molecular properties or virulence factors these NE-causing strains have that enable them to effectively compete and selectively proliferate in the gut to produce tissue damage. So far, no particular genetic type of C. perfringens has been identified that causes NE. Cluster analysis of C. perfringens isolates from intestinal tracts of healthy chickens and chickens with NE did not show that NE is caused by C. Perfringens strains that belong to a specific genotypic lineage.
The pathogenesis of NE is not fully understood. There is convincing evidence that C. perfringens strains vary in virulence and that NE is caused by certain strains of the organism (“NE strains”). Why these are capable of inducing NE remains unknown. Several studies have shown that in a NE outbreak, a single virulent strain displaces the genetically heterogeneous enteric population of C. perfringens in the intestinal tract of the chicken. However, it is not clear what molecular properties or virulence factors these NE-causing strains have that enable them to effectively compete and selectively proliferate in the gut to produce tissue damage. So far, no particular genetic type of C. perfringens has been identified that causes NE. Cluster analysis of C. perfringens isolates from intestinal tracts of healthy chickens and chickens with NE did not show that NE is caused by C. Perfringens strains that belong to a specific genotypic lineage.
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| The small intestine from a 31-day-old chicken affected with NE is dilated and thin. Only birds that have been euthanised or died very recently can be evaluated as the changes seen here can develop postmortem as gas increases in the gut after the bird dies. |
However, the amount of alpha toxin produced by C. perfringens isolated from NE lesions is not significantly different from the amount of the toxin produced by isolates from the intestine of healthy birds. Recently, another novel toxin (NetB) has been identified in certain strains of C. perfringens. Initially, this toxin was thought to be the major and critical virulence factor in C. perfringens strains capable of causing NE, but recently published research indicates that NetB-negative strains are also capable of causing NE in experimentally challenged chickens. Certainly, the role of NetB as a virulence factor in the pathogenesis of NE needs further investigation.
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Source: World Poultry, Vol. 27, No. 6
