Pancreatitis-Type DHAV-1: An Emerging Pathological Presentation in Ducks

Duck hepatitis A virus type 1 (DHAV-1) is traditionally associated with acute hepatitis, haemorrhage and necrosis of the liver in young ducklings. However, a distinct form known as pancreatitis-type DHAV-1 has also been identified. This presentation is characterised by prominent pancreatic lesions, with comparatively limited pathological changes in the liver. Recognising this difference is important when investigating atypical cases of duck viral hepatitis. 

Distinguishing Pancreatitis-Type DHAV-1^[1],[2] 

Pancreatitis-type DHAV-1 was identified in outbreaks involving Muscovy ducklings in China. Unlike classical DHAV-1 infection, which predominantly affects the liver, this form produces yellowish discolouration and haemorrhagic changes in pancreatic tissue (Zhu et al., 2019). 

To investigate these differences, researchers experimentally infected Muscovy ducklings with hepatitis-type and pancreatitis-type DHAV-1 strains. The hepatitis-type strain produced more efficient viral replication in the liver, accompanied by characteristic hepatic lesions. In contrast, the pancreatitis-type strain showed greater replication in the pancreas, with prominent pancreatic lesions and no significant pathological changes in the liver. 

These findings demonstrated that the two forms have distinct tissue distribution and pathogenic characteristics. 

Gross and Histopathological Findings^[1],[2] 

During post-mortem examination, pancreatitis-type DHAV-1 infection may produce a visibly yellowish or haemorrhagic pancreas. These changes contrast with the enlarged liver and petechial or ecchymotic haemorrhages typically associated with classical hepatitis-type infection. 

Histopathological examination provides further evidence of pancreatic injury. Infection with the pancreatitis-associated strain produced extensive apoptosis of pancreatic acinar epithelial cells. Increased caspase-3 expression was also observed in pancreatic tissue, indicating the involvement of cellular apoptosis in the development of these lesions. 

The distinction between gross and microscopic findings is important because pancreatic involvement may not be recognised if the examination focuses exclusively on the liver. 

Metabolic Changes Associated with Pancreatic Infection^[1],[3] 

Pancreatic tissue analysis has also identified differences in the expression of metabolism-associated genes between ducks infected with classical and pancreatitis-associated DHAV-1 strains. Changes were observed in genes associated with amino acid metabolism, calcium signalling and immune responses. 

In particular, differences involving glycine, serine and threonine metabolism suggest that metabolic disturbances may contribute to the distinct pathological presentations of these strains. However, the precise mechanisms linking these metabolic changes to pancreatic injury remain unclear. 

Implications for Veterinary Pathology 

When investigating suspected DHAV infection, veterinarians should examine the pancreas alongside the liver during post-mortem assessment. Yellowish discolouration, haemorrhage or pancreatic tissue damage should prompt further investigation, particularly when typical hepatic lesions are absent. 

Histopathological examination, combined with molecular detection of DHAV-1, can help establish the nature of the infection. Recognising pancreatitis-type DHAV-1 broadens the pathological understanding of duck viral hepatitis and highlights why examination of multiple organs is important during disease investigation.

References:

1. Zhu T, Qi B, Liu R, Jiang X, Lu R, Xiao L, Fu G, Fu Q, Shi S, Wan C, Huang Y. Comparative pathogenicity of two subtypes (hepatitis-type and pancreatitis-type) of duck hepatitis A virus type 1 in experimentally infected Muscovy ducklings. Avian Pathology. 2019 Jul 4;48(4):352-61. https://www.tandfonline.com/doi/pdf/10.1080/03079457.2019.1605146
2. Zhang Y, Wu S, Liu W, Hu Z. Current status and future direction of duck hepatitis A virus vaccines. Avian Pathology. 2023 Mar 4;52(2):89-99. https://www.tandfonline.com/doi/pdf/10.1080/03079457.2022.2162367
3. Chen Z, Shi SH, Huang Y, Huang CQ, Liu RC, Cheng LF, Fu GH, Chen HM, Wan CH, Fu QL. Differential metabolism-associated gene expression of duck pancreatic cells in response to two strains of duck hepatitis A virus type 1. Archives of virology. 2021 Nov;166(11):3105-16. https://link.springer.com/content/pdf/10.1007/s00705-021-05199-4.pdf