Turkey Viral Hepatitis
Turkey viral hepatitis is caused by a picornavirus. TVH virus was determined to have sequence similarity to other picornaviruses, but phylogenetic analyses indicate that this virus could not be classified within presently recognized picornavirus genera. The virus is thermostable; resistant to ether, phenol, and creolin but not formalin; and susceptible to high, but not low, pH.
Turkey viral hepatitis usually is a subclinical disease that becomes apparent as a result of stresses due to environmental conditions or concurrent infection. Clinical signs in TVH-affected birds are not well defined. Variable degrees of depression may be observed in affected flocks, but more commonly disease is characterized by sudden deaths of apparently healthy birds. Morbidity and mortality vary according to the severity of stress. In poults less than 6 weeks of age, morbidity may reach 100% and mortality 10%-25%. Breeder flocks may have decreased egg production, fertility, and hatchability, but this has not been conclusively determined.
Gross lesions are confined to the liver and pancreas. Livers generally are enlarged. Lesions consist of focal, gray, sometimes depressed areas up to several millimeters in diameter. Lesion distribution is variable; birds that die usually exhibit extensive lesions that often coalesce and may be masked by vascular congestion and hemorrhage. Gross lesions in the pancreas are less frequently observed than hepatic lesions. Lesions in the pancreas generally are roughly circular, gray-to-pink, and may extend across a lobe. .
A presumptive diagnosis of TVH may be obtained by histopathology; the presence of lesions in both the liver and pancreas are highly suggestive of this disease. However, similar lesions in the liver are produced by other pathogens, including Salmonella spp., Pasteurella multocida, avian adenoviruses, reovirus, and Histomonas meleagridis.
Virus isolation is accomplished by inoculation of 5- to 7-day-old embryonated chicken eggs by the yolk sac route. Preferred clinical samples include liver, pancreas, spleen, kidney, intestinal contents, and droppings.
Reverse-transcriptase PCR can detect TVH viral RNA in tissues, intestinal contents, or droppings.
Turkey viral hepatitis is a picornavirus disease of young turkeys characterized by the presence of hepatitis with or without pancreatitis. The disease also has been linked to decreased egg production, fertility, and hatchability in breeder hens.
Diagnosis of TVH is based on histopathology, virus isolation, or detection of viral RNA by reverse-transcriptase PCR. Preferred clinical samples include liver, pancreas, spleen, kidney, intestinal contents, and droppings.
No specific treatment or preventive measures are available. Prevention of stress and other infections help prevent normally subclinical disease from developing into TVH.