Coronaviral enteritis is an acute, highly contagious disease of turkeys characterized by listlessness, anorexia, diarrhea, and decreased weight gain in young turkeys, with egg production losses in turkey breeder hens. The causative agent is turkey coronavirus (TCV). Severity of the disease is often compounded by the presence of other enteric pathogens. Diagnosis can be confirmed by virus isolation from the GI tract or feces, detection of TCV RNA by RT-PCR assay, or serological testing for anti-TCV antibodies. No specific treatment is available; however, antimicrobial treatment decreases losses from secondary bacterial infections and may decrease mortality.
Epidemiology and Transmission of Coronaviral Enteritis of Turkeys
Turkey coronavirus (TCV) has been identified in turkeys in the US, Canada, Brazil, Italy, the UK, and Australia. The disease affects turkeys of all ages; however, clinical signs of disease are most commonly observed in young turkeys during the first few weeks of life. Turkeys are the only natural host for TCV to have been identified.
Transmission of TCV is horizontal, and the virus is shed in the feces of infected birds and also spread via feces-contaminated fomites. Infected turkeys shed the virus for several weeks after recovery. The virus generally spreads rapidly through a flock, from flock to flock within a farm, and between adjacent farms. Mechanical transmission of the virus can occur by movement of people, contaminated equipment (including vehicles), and insects. Darkling beetle larvae and domestic house flies are potential mechanical vectors. Wild birds, rodents, and dogs also can serve as mechanical vectors. There is no evidence that TCV is egg transmitted; however, poults may become infected in the hatchery via contaminated personnel and fomites such as egg boxes from infected farms.
Clinical Findings of Coronaviral Enteritis of Turkeys
Clinical signs of TCV occur suddenly. While the morbidity rate generally approaches 100%, the mortality rate is variable. Incidence of high mortality may depend on the age of the birds at the time of infection, concurrent infections, environmental conditions, and management practices.
Turkeys affected by coronaviral enteritis may exhibit the following clinical signs:
listlessness
anorexia
decreased water consumption
watery diarrhea
dehydration
weight loss, growth depression, and poor feed conversion
Breeder hens exhibit a rapid drop in egg production. Egg quality also is affected; hens produce white, chalky eggs lacking normal pigmentation.
Lesions
Gross lesions of TCV are primarily observed in the GI tract. The duodenum and jejunum may appear pale, thin-walled, and flaccid; ceca are distended with gas and watery contents. Atrophy of the cloacal bursa (bursa of Fabricius) may also be observed.
Microscopic lesions consist of a decrease in intestinal villous length and an increase in crypt depth; intestinal columnar epithelium changes to cuboidal epithelium and loses microvilli. Other changes include a decrease in the number of goblet cells, separation of enterocytes from the lamina propria, and infiltration of the lamina propria with heterophils and lymphocytes.
In the cloacal bursa, the normal pseudostratified columnar epithelium is replaced by stratified squamous epithelium, and considerable heterophilic inflammation is observed within and underneath the epithelium.
Diagnosis of Coronaviral Enteritis of Turkeys
Virus isolation
RT-PCR assay
Antigen detection
Due to the similarity of clinical signs and gross lesions associated with enteric diseases in turkeys, laboratory diagnosis is required to confirm the presence of TCV in affected flocks.
Preferred clinical samples for diagnostic analyses include serum, intestinal contents, and fresh tissues (intestines and cloacal bursa) from clinically affected birds. Once samples are collected, they should be kept cold (on ice or at 4°C) during storage and transport to the laboratory. Diagnostic confirmation can be obtained in the following ways:
virus isolation in chicken or turkey embryos
detection of TCV antigen or RNA in preferred tissues by immunohistochemical testing and real-time RT-PCR and RT-PCR assay, respectively
detection of TCV antibodies in serum using indirect immunofluorescence assay or ELISA
TCV must be distinguished from other enteric viral, bacterial, and parasitic infections, including those caused by astrovirus, rotavirus, reovirus, Salmonella spp, and cryptosporidia.
Prevention and Treatment of Coronaviral Enteritis of Turkeys
Strict biosecurity practices
Antimicrobials
Prevention of TCV through strict biosecurity practices is the preferred method of control. Infected turkeys shed virus in feces for prolonged periods after recovery. In addition, fecal contamination and contaminated fomites (eg, clothing, boots, equipment, feathers, and vehicles) are potential sources of infection for other susceptible turkeys. Other potential vectors include wild birds, rodents, dogs, and flies.
Pearls & Pitfalls
|
There is no specific treatment for TCV enteritis. Antimicrobial treatment decreases mortality rate, most likely by controlling secondary bacterial infections; however, treatment does not mitigate growth depression.
Effective management procedures to decrease mortality rate include raising brooder house temperatures and avoiding crowded conditions. Elimination of TCV from contaminated premises is accomplished by depopulation, followed by thorough cleaning and disinfection of houses and equipment. After cleaning and disinfection, premises should remain free of birds for a minimum of 3–4 weeks.
Zoonotic Risk of Coronaviral Enteritis of Turkeys
Although interspecies recombination has been demonstrated between infectious bronchitis virus (IBV) and turkey coronavirus (TCV), there is no evidence of zoonotic transmission of TCV.
Key Points
TCV affects turkeys of all ages, but clinical signs of disease occur most commonly in young turkeys during the first few weeks of life and are characterized by acute enteritis with high mortality.
Breeder hens exhibit decreased egg production and egg quality.
Diagnosis of coronaviral enteritis is dependent upon laboratory assays (serological, virus isolation, immunohistochemical, or RT-PCR). Preferred clinical samples include serum, intestinal contents, and fresh tissues (intestines, cloacal bursa).
Strict biosecurity measures are the only means of control to prevent exposure of susceptible turkeys to infected turkeys, contaminated fomites, and potential vectors.
For More Information
Guy JS. Turkey coronavirus enteritis. In: Swayne DE, ed. Boulianne M, Logue CM, McDougald LR, Nair V, Suarez DL, associate eds. Diseases of Poultry. 14th ed. Wiley; 2020:402-408.
Guy JS, Vaillancourt JP. Turkey coronavirus. In: Brugere-Picoux J, Vaillancourt JP, Shivaprasad HL, Venne D, Bouzouaia M, eds. Manual of Poultry Diseases. French Association for the Advancement of Science; 2015:242-247.
