Coronaviral Enteritis of Turkeys: Introduction

Coronaviral Enteritis of Turkeys: Introduction
(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 failure to gain body weight in adult birds may be more important economically.

Etiology and Epidemiology:

The causative agent is a coronavirus, but the clinical disease is often complicated by other intestinal viral, bacterial, and protozoal infections. Spread is by direct or indirect contact with infected birds or contaminated premises. Droppings of acutely infected birds are rich in virus, and recovered birds may continue to shed lower levels of virus for months. Environmental factors do not appear to influence the occurrence; however, cold temperatures may contribute to the severity of the disease. Cold weather, especially freezing, and high litter moisture increase 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.

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:

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. 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 including 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 naive 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 ( Hexamitiasis: Introduction), salmonellosis ( Salmonelloses: Introduction), 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 because carrier states may be induced.

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. Antibiotic administration decreases mortality but not the growth suppressant effects. 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 crop mycosis, a common sequela of longterm antibiotic therapy.