Turkey Viral Hepatitis
Also Known As: TVH — Turkey Hepatopancreatitis
Caused By: Turkey Viral Hepatitis Virus — TVHV — THV
Introduction
Turkey viral hepatitis (TVH) is caused by a virus of the family Picornaviridae but is at present not classified any further.
TVH is a highly contagious but generally subclinical disease.
Distribution
TVH is reported in Canada, USA, Italy and the UK. Its distribution may be greater than this as monitoring is difficult due to the often subclinical nature of the disease.
Transmission is principally from faeces and can be direct or indirect. It is possible that vertical transmission also occurs.
Signalment
TVH affects only turkeys (Meleagris gallopav). Disease occurs primarily in young, <6 weeks old birds.
Clinical Signs
When clinical disease does develop, it is characterised by anorexia, weight loss, depression and sudden deaths. As the hepatopathy develops, neurological signs may also develop.
Decreased hatchability and a drop in egg production are often also seen.
Diagnosis
TVH is characterised by multifocal hepatic necrosis consisting of grey lesions that may be depressed and up to several mm in diameter +/- accompanying pancreatic necrosis at post-mortem. When present, pancreatic lesions are grey-pink and circular and can be very extensive. Vascular congestion and haemorrhage are often seen in fatal cases.
Microscopic changes are similar in both organs: vacuolation and mononuclear cell infiltrates are seen with bile duct proliferation. Blood often pools around areas of focal necrosis and necrotic cells are visible scattered among the leucocytes. Proliferating reticuloendothelial cells often form giant cells.
Virus isolation is the only other method of diagnosis. It can be achieved using liver, pancreas, spleen, kidney or faeces. Liver is preferred. Homogenised tissues or filtered faeces are inoculated into embryonated chicken eggs and observed for embryonic death and congestion or yolks are harvested. The virus can only be isolated from tissues and faeces until 28 days post infection.
Treatment and Control
No specific treatment or control measures are available. Minimisation of stress and faecal contamination may help.
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References
Animal Health & Production Compendium, Turkey Viral Hepatitis datasheet, accessed 03/07/2011 @ http://www.cabi.org/ahpc/
Animal Health & Production Compendium, Turkey Viral Hepatitis Virus datasheet, accessed 03/07/2011 @ http://www.cabi.org/ahpc/
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