Clostridium perfringens-induced necrotic enteritis and related subclinical disease have become economically significant problems for the broiler industry. Fortunately, scientific interest in this topic has grown: new C. perfringens virulence factors have been discovered and new insight gained about the pathogenesis of necrotic enteritis. It has been shown that alpha toxin, for a long time thought to be the key virulence factor, is not essential for the development of the disease. Moreover, it is now clearly established that only certain C. perfringens strains are capable of inducing necrotic enteritis under specific conditions that predispose to the disease and they constitute only a minority in the intestinal tract of healthy chickens. A novel pore-forming toxin, NetB, has been identified in these virulent avian C. perfringens strains. Using a gene knockout mutant, it has been shown that NetB is a critical virulence factor in the pathogenesis of necrotic enteritis in broilers. In addition to toxin production, other factors have been described that contribute to the ability of certain C. perfringens strains to cause necrotic enteritis in broilers. It has been suggested that proteolytic enzymes play an important role in the initial stages of necrotic enteritis since the villi are first affected at the level of the basement membrane and the lateral domain of the enterocytes. In field outbreaks of necrotic enteritis, a single clone of C. perfringens is dominant in intestines of all affected birds, as opposed to the mixture of different C. perfringens strains that can be isolated from healthy bird intestines. It has been proposed that bacteriocin production is responsible for the dominance of a single strain in necrotic enteritis cases. Furthermore, it has been shown that virulent strains are more able to adhere to extracellular matrix molecules than non-virulent strains. The current knowledge on the pathogenesis of the disease has been summarized in this short review.

https://www.tandfonline.com/doi/pdf/10.1080/03079457.2011.590967

Necrotic enteritis in broilers: an updated review on the pathogenesis.

Effect of dietary protein concentrates on the incidence of subclinical necrotic enteritis and growth performance of broiler chickens

Well known as the cause of necrotic enteritis, C. perfringens (CP) is now recognized as causing a spectrum of effects including subclinical infection, mild disease with focal intestinal necrosis, diarrhoeal illness and liver disease, as well as the classic form of acute fulminant necrotizing enteritis. The mild and subclinical forms of infection appear to be widespread, and, possibly increasing in incidence. Furthermore, bacterial enteritis is increasingly being recognized less as an invasion by pathogenic organisms per se and more as an expression of the normal process by which the intestinal bacterial population changes overtime in response to changes in the intestinal environment. Such shifts in enteric bacterial populations have been referred to as dysbacteriosis. Management of the microbial ecology of the intestinal tract is therefore an important element of preventing disease, enhancing performance, and preventing foodborne illness. Diagnosis of emerging forms of bacterial enteritis including CP infection can be challenging and involves a comprehensive analysis of flock history and condemnation records, clinical signs, gross and histopathology, bacterial culture and empirical response to treatment, augmented by molecular techniques where available. Control measures are at present based on extensions of validated approaches to the control of the classical form of the disease: managing known risk factors for necrotic enteritis (coccidiosis, diet and litter quality) and the use of approved antimicrobial agents with proven efficacy against CP.

Manifestations of Clostridium perfringens and related bacterial enteritides in broiler chickens

1. The effect of three different levels of dietary trypsin inhibitor activity (achieved by varying the amount of non-toasted full fat soya bean in replacement for toasted full fat soya bean) on the incidence of spontaneously-occurring sub-clinical necrotic enteritis (NE) in broiler chickens was compared. A fourth dietary treatment compared the effect of a diet that used potato protein concentrate as the major protein source. The determined trypsin inhibitor activity increased with the increasing content of non-toasted soya bean: 1·90, 6·21, 8·46 and 3·72 mg/g for the three soya bean diets (0, 100 and 200 g of non-toasted soya bean/kg) and the potato protein diet respectively. 2. Although increasing amounts of the non-toasted full-fat soya bean increased the feed intakes of the birds, there was a marked reduction in protein digestibility, weight gain and feed conversion efficiency. 3. There was a linear increase in sub-clinical NE lesions in the duodenum, jejunum, mid small intestine and ileum with increasing non-toasted soya bean. Caecal Clostridium perfringens counts increased with the increasing dietary content of non-toasted soya bean. Serum α-toxin antibodies were higher in the birds fed the 200 g non-toasted soya bean/kg diet compared with the other diets. 4. The results demonstrated that variation in the amount of non-toasted dietary soya bean not only affects growth performance of broilers but also affects the incidence of sub-clinical necrotic enteritis in the flock. Ensuring the lowest possible trypsin-inhibitor activity in soya bean samples is a valuable tool to improve the health and welfare of birds and in reducing the financial losses from this disease.

Effect of trypsin inhibitor activity in soya bean on growth performance, protein digestibility and incidence of sub-clinical necrotic enteritis in broiler chicken flocks.

The tools available for monitoring necrotic enteritis caused by Clostridium perfringens in broiler chickens have been limited, particularly for identifying subclinical disease. In this study, a modified enzyme-linked immunosorbent assay was used to quantify levels of specific immunoglobulin G to C. perfringens alpha-toxin in serum from broilers. We found significantly higher antibody levels in broilers with a history of subclinical necrotic enteritis compared with a zinc-bacitracin-treated group with a low level of gut lesions. Furthermore, in 4.5-week-old commercial broiler flocks, there was an association between the occurrence of C. perfringens-associated hepatitis at slaughter and the immune response to alpha-toxin. Practical solutions for defining cut-off levels for positive serum samples at individual and flock levels are proposed, and were found to be useful on a set of samples available from flocks with different histories regarding the occurrence of C. perfringens-associated disease. This serolog...

Diagnosing Clostridium perfringens-associated necrotic enteritis in broiler flocks by an immunoglobulin G anti-alpha-toxin enzyme-linked immunosorbent assay.

Forty-five broiler carcasses from 6 different flocks were condemned due to liver lesions at processing meat inspection, and collected for pathological and bacterial examinations. All affected chickens showed liver enlargement with discolouration and an apparent acinar pattern. The enlarged gallbladder and the extrahepatic bile ducts contained yellow inspissated cream-coloured material. Histopathologically, extensive proliferation of bile ductules with fibrosis was observed in interlobular connective tissue, and it spread to form bridges with adjoining triads. Destruction and obstruction of portal bile ducts with multiple granulomas due to bacterial infection and outflow of the bile were frequently observed. Many Gram-positive bacilli were seen in the lesions, and they were identified as Clostridium perfringens by indirect immunofluorescence staining technique. Clostridium perfringens was isolated from affected livers. These findings are consistent with cholangiohepatitis. Therefore, it is suggested that C. perfringens might be important in the pathogenesis of cholangiohepatitis in broiler chickens.

/pdf/cholangiohepatitis-in-broiler-chickens-in-japan-3ga6m7pgmk.pdf

Cholangiohepatitis in broiler chickens in Japan: histopathological, immunohistochemical and microbiological studies of spontaneous disease.

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Cholangiohepatitis in broiler chickens in Japan: histopathological, immunohistochemical and microbiological studies of spontaneous disease.