Avian Necrotic enteritis: Pakistan is an agricultural country and a large portion of population is linked with this. Livestock is an integral part of agriculture sector and it contributes to the agricultural and national GDP up to 56% and 13%, respectively. Poultry industry has gained much expansion since 1970 and it gives contribution of 11% and 2% in livestock and national GDP. Poultry industry provides cheaper, readily available and good source of animal protein in the form of poultry meat, eggs and byproducts.
Enteric diseases are important concern to poultry industry because these diseases effect the economics of industry in different ways including decreased production, low feed conversion efficiency of poultry birds and increased production cost in terms of medication.
Necrotic enteritis is an important enteric disease in poultry caused by Clostridium perfringens type A and this disease was reported first time by Perish in 1961. Necrotic enteritis costs to the global poultry up to 5 billion US dollars per annum in terms of medication cost and poor growth of poultry birds. In broiler, it usually occurs between 2nd to 5th week of age and mortality is up to 2-10%.
Clostridium perfringens is an anaerobic, gram positive, non-motile, spore forming bacterium readily present in the soil, feces and poultry litter. It is normal inhabitant of the gastrointestinal tract of the poultry birds.
Clostridium perfringens have 5 toxinotypes including type A, B, C, D and E and these toxinotypes are mainly based on different types of toxins produced like alpha, beta, epsilon, iota and enterotoxins. These toxins are exotoxins and are mainly responsible for the production of clinical signs and disease in animals and poultry birds. C. perfringens type A mainly produces alpha toxin.
There are several predisposing factors which elicit the clinical signs and lesions of necrotic enteritis in the poultry birds including coccidiosis, presence of pathogenic C. perfringens, feed composition like high protein diet, stress, poor immune status, mycotoxins, lack of biosecurity, bad managemental conditions and other concurrent diseases like salmonellosis etc.
- perfringens is a normal inhabitant of chicken’s gut microbiota and usually remain in low number under healthy conditions (102-104 cfu/g of ileal digesta) but when conditions in the intestinal tract changes, lead to the increase in the number of the pathogenic C. perfringens (107-108) and produce toxins lead to the development of disease with the production of lesion in the small intestine of the birds.
Regulation of toxin gene expression in C. perfringens:
In C. perfringens, expression of toxin gene is regulated by tow component regularity system including VirR/VirS system, which is present in type A. Two types of cell signaling like agr and AI-2 signaling is important for regulation of toxin genes.
Necrotic enteritis mainly occurs in two forms including clinical and subclinical. Typical clinical signs of necrotic enteritis include depression, reluctance to move, diarrhea, loss of appetite, dehydration, ballooning of the intestine due to gas accumulation and sometime ulcers or light yellow spots on the surface of intestine can be seen. It is believed that sub clinical form of the disease has more negative impact of the economics and performance of the birds.
Effected birds have dehydration, dark colored breast muscles, severe inflammation of the duodenum and ileum, distension of intestines due to accumulation of gas and mucosa of the intestine is covered with a diphtheroid membrane known as “Turkish Towel”. In advanced cases, sloughing of the intestinal mucosa along with areas of necrosis can be observed. In some cases, cholangeiohepatitis and gizzard erosions are seen.
Initially microscopic lesions are developed at the apices of the intestinal villi which are characterized by the sloughing of the epithelium then these lesions are extended up to crypts, submucosa and muscular layers of the intestine. Coagulative necrosis along with large number of inflammatory cells can be seen.
Diagnosis of the disease can be performed through case history, clinical signs, lesions, gram’s staining, biochemical tests, ELISA (enzyme linked immunosorbent assay) and PCR (polymerase chain reaction).
Treatment of necrotic enteritis is usually done through a list of antibiotics including Penicillin, Amoxicillin, Ampicillin and Erythromycin etc. Several strategies are developed as non-antibiotic feed formulation treatments to control necrotic enteritis.
Necrotic enteritis can be controlled by following ways including
- Strict monitoring
- Farm hygiene
- Stabilizing the gut flora by using Prebiotics, Enzymes, Acids and Essential oils
- Feed quality
- Treatment and Vaccination