To identify a candidate etiologic agent for turkey viral hepatitis, we analyzed samples from diseased turkey poults from 8 commercial flocks in California, USA, that were collected during 2008–2010. High-throughput pyrosequencing of RNA from livers of poults with turkey viral hepatitis (TVH) revealed picornavirus sequences. Subsequent cloning of the ≈9-kb genome showed an organization similar to that of picornaviruses with conservation of motifs within the P1, P2, and P3 genome regions, but also unique features, including a 1.2-kb sequence of unknown function at the junction of P1 and P2 regions. Real-time PCR confirmed viral RNA in liver, bile, intestine, serum, and cloacal swab specimens from diseased poults. Analysis of liver by in situ hybridization with viral probes and immunohistochemical testing of serum demonstrated viral nucleic acid and protein in livers of diseased poults. Molecular, anatomic, and immunologic evidence suggests that TVH is caused by a novel picornavirus, tentatively named turkey hepatitis virus.
Turkey viral hepatitis (TVH) is a highly infectious disease affecting young turkey poults. The disease is often subclinical, causing minor histologic lesions, and becomes overt when the animals are stressed, resulting in varying rates of illness and death. Mortality rates of up to 25% have been reported. Diagnosis is based on characteristic lesions in the liver, which include multifocal necrosis and mononuclear inflammatory cell infiltrates. Similar lesions may be found in the pancreas. Clinical signs include anorexia, depression, diarrhea, and weight loss compatible with a diagnosis of enteritis, the second most common diagnosis made in turkey poults throughout the United States. Although we cannot with confidence estimate the specific burden of TVH, its economic effects are likely substantial; in the United States, turkey production was valued at $3.71 billion in 2007. The identification of a pathogen and development of specific diagnostics will lead to better understanding of the economic consequences and other effects of TVH.
The disease has been experimentally reproduced in turkey poults by inoculation with material derived from affected animals. A viral basis for TVH has been presumed since its initial description in 1959 because the causative agent passed through 100-nm membranes, was acid stable, was not affected by antimicrobial drugs, and could be propagated in the yolk sac of embryonated chicken eggs. Icosahedral particles of 24 to 30 nm have been found by electron microscopy (EM) in liver lesions of birds, as well as in embryonated turkey eggs that have been inoculated with material derived from affected birds; however, no agent has been consistently implicated.
Emerging Infectious Diseases
March 22, 2011
Original web page at Emerging Infectious Diseases