Coronaviral Enteritis Of Turkeys
(Bluecomb, Transmissible enteritis) Coronaviral enteritis is an acute, highly contagious disease of turkeys characterized by sudden onset, marked depression, anorexia, diarrhea, dehydration, and weight loss. Mortality may be high, particularly in poults, but loss of condition in growing and adult birds may be more important economically. Etiology and Epidemiology:The causative agent is a coronavirus, but the clinical disease is complicated by other intestinal viral, bacterial, and protozoal infections. Spread is by direct or indirect contact with infected birds or contaminated premises. Droppings of infected birds are rich in virus, and recovered birds may continue to shed virus for months. Environmental factors do not appear to influence the occurrence; however, environmental stresses may contribute to the severity of the disease. Cold weather, especially freezing, increases survival of the virus. Clinical Findings:A short incubation period, often 48-72 hr, is followed by general depression, anorexia, and diarrhea in the flock. Young poults appear cold, chirp constantly, and seek heat. Feed and water consumption drop markedly, and poults lose weight rapidly. Morbidity and mortality may approach 100% in uncontrolled outbreaks. Young birds have few lesions other than flaccid, distended intestines that contain excess fluid and gas. Ceca are distended with foamy, pale brown, fetid fluid. Morbidity and mortality are variable in growing and adult turkeys. Profuse diarrhea, with mucoid threads or casts in the droppings, is common. Dehydration and weight loss are often pronounced, and several weeks may be required for normal growth to resume. Cyanosis of the head is common. Breeder hens experience a severe drop in egg production and produce abnormal eggs with chalky shells. Vertical transmission does not occur. Lesions in older birds are more extensive. Skin and musculature are dehydrated, and petechial hemorrhages may be seen on the viscera. Kidneys frequently are swollen and contain an excess of urates, and the pancreas may have multiple, chalky white areas. Severe catarrhal enteritis is common, and mucoid casts may be present. The crop may be distended and contain sour-smelling fluid. The spleen is often small and pale gray. Diagnosis:Although clinical findings and lesions are suggestive, definitive diagnosis requires laboratory techniques. Among these are demonstration of coronaviral antigen in intestines of affected birds by direct fluorescent antibody techniques, detection of coronavirus particles in intestinal contents by electron microscopy, reproduction of the disease in SPF poults with bacteria-free intestinal filtrates, and negative findings for common bacterial and protozoal infections. Other conditions that may produce similar signs in poults include Hexamitiasis, Salmonelloses, inanition, and water deprivation. Other intestinal viruses (which are common in commercial flocks, including rotavirus, reovirus, astrovirus, enterovirus, and possibly others) can cause disease that resembles mild coronaviral enteritis. In older birds, severe larval ascarid infection may cause diagnostic confusion. Prevention and Treatment:Introduction of virus should be minimized by good management and sanitation practices. Depopulation of problem premises followed by thorough cleaning and disinfection of buildings and equipment is effective in breaking the cycle of infection. Such farms are best cleaned during summer and should be left vacant for =1 mo. A commercial vaccine is not available. “Controlled” exposure programs have been used with variable success on some problem farms, but such procedures are not recommended except in unusual circumstances. The course of disease outbreaks may be altered by good nursing care and judicious use of antibiotics and other drugs to combat secondary bacterial infections and dehydration. Birds in brooder houses should be provided with supplemental heat, and birds on range should be protected from adverse environmental conditions. The selection of an antibiotic is empiric at best, but tetracyclines, neomycin, streptomycin, lincomycin, penicillin, and bacitracin are among those used with variable success. Antibiotics may be added to drinking water in combination with calf milk-replacer and electrolyte, eg, 25 lb (11.4 kg) of calf milk-replacer and 450 g of potassium chloride to 100 gal. (380 L) of water. Birds should be medicated for 7-10 days. During and after treatment, birds should be observed closely for secondary intestinal mycosis, a common sequela of antibiotic therapy. |
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