Turkey Coronavirus

Also Known As – TCoV – Bluecomb disease Virus – Turkey Enteritis Virus – Transmissible Enteritis Virus

Introduction

Turkey Coronaviruses are members of the Coronaviridae family and fall into two categories: Bovine Coronavirus-like turkey isolates (TCoV-B) and IBV-like Turkey Coronaviruses (TCoV-I). The TCoV-I viruses are very closely genetically related to Infectious Bronchitis Virus.

Gastrointestinal disease is the main result of coronavirus infection in turkeys.

TCoVs are not zoonotic.

Distribution

Turkey Coronaviral enteritis, (TCE) caused by TCoV-B, has only been confirmed in the USA and Canada but TCoV-I has recently been isolated in Britain.

Transmission is via the faecal-oral route and can be spread by people, vehicles and vermin.

Signalment

Poults are most severely affected by coronavirus infection.

It is now thought that other avian species may be able to asymptomatically harbour TCoV.

Clinical Signs

Disease is most severe and mortality highest in poults.

The most common manifestation is of gastrointestinal disease, causing white, green or yellow diarrhoea, anorexia, Inappetance and malaise. Concurrent dehydration, hypothermia, pyrexia and weakness may occur. The skin of adult birds is often seen to darken. Birds often exhibit a drooped wing appearance. Morbidity is usually 100% and bird are often seen to be huddling together.

Neurological disease develops in some birds, producing a head tilt, depression and ataxia.

TCoV is also one of a group of pathogens associated with Poult Enteritis and Mortality Syndrome (PEMS) which affects poults up to one month old in the USA causing huge spikes in mortality.

Recovery begins after approximately 5 days but it may take several weeks to regain weight. Recovered birds will not become ill again but do shed the virus for months afterwards and carry it for life.

Diagnosis

Clinical signs are suggestive but not diagnostic of TCE or PEMS. Starvation and other viral pathogens can appear very similarly.

At post-mortem, birds with TCE have swollen, pale, flaccid duodenums with a mononuclear cell infiltrate intraluminally. Epithelial lesions are most severe in the jejunum. Villous stunting and atrophy is evident on histological analysis. Nucleoli may appear pronounced in infected cells. Goblet cells decrease in number and epithelial separation may be seen.

Electron microscopy can be used to look for Coronaviral particles in gut contents but this is often challenging. Indirect Immunofluorescence and immunoperoxidase staining using antibodies form convalescent turkeys can demonstrate TCoV in intestinal sections. A modified ELISA is capable of detecting antibodies to TCoV, derived from a commercially available test, which is promising for disease screening in the future. Reverse PCR designed for IBV can also be used successfully for TCoV-Is.

Treatment

Ameliorative therapies include supplying heat, calf milk replacer, potassium chloride added to milk suspension, antibiotics and copper sulphate.

Control

No vaccine is available but birds that recover are immune for life.

Because of the carrier state, farms should be depopulated after a TCE outbreak. Access to farms should be limited as part of general biosecurity measures and it should be considered that marketed birds have unknown TCoV status.

Turkey Coronavirus Learning Resources
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References

Animal Health & Production Compendium, Turkey Coronaviruses datasheet, accessed 21/06/2011 @ http://www.cabi.org/ahpc/

Animal Health & Production Compendium, Turkey Coronavirus infections datasheet, accessed 21/06/2011 @ http://www.cabi.org/ahpc/