Prevalence of a virus similar to human hepatitis B virus in swine

Abstract

Background: The objective of this study is to established evidence of the existence of a novel member of the hepadnavirus family endemic in swine. Temporarily this virus was designated as swine hepatitis B virus (SHBV). This SHBV can be detected by using human hepatitis B virus diagnostic kits including ELISA, immunohistochemical staining, and transmission electron microscopy (TEM). Also seroprevalence of pig farms in Beijing, China, and pathological features of SHBV infection was determined.

Results: Screened result shows that overall prevalence of HBsAg was 24.8%, closed to that of anti-HBsAg, whereas HBeAg and anti-HBe were barely detectable. The distribution of HBsAg and HBcAg was examined by immunohistochemistry of liver samples. Typical hepatitis pathological change, such as spotty parenchymal cell degeneration, necrosis of hepatocytes and proliferation of fibrous connective tissue were observed during histopathological analysis. Analysis of HBsAg-positive serum with TEM revealed two morphologic forms, 20 nm and 40 nm sized particles, similar to small spherical and Danes particles of HBV. Observation of the ultrastructure of the liver also found HBV-like particles in the nucleus of hepatocytes.

Conclusion: Our research result implies that SHBV could be a causative agent of swine. The discovery of SHBV will unveil novel evolutionary aspects of hepatitis and provides new information for further hepadnavirus research.

Figure 1

Prevalence of SHBV serological markers among 416 swine sera samples collected from five farms in Beijing, China. Scatter graphs showed that nearly a quarter of the swine have been infected by SHBV. Prevalence rates of HBs were close to anti-HBs, while HBeAg and anti-HBe were hardly detected.

Figure 2

Results of histopathological analysis(A, B) and Mallory's trichrome stain(C, D). (A) desmoplasia between hepatic lobule (arrow), (B) infiltration of lymphocytes (down arrow), hyperplasy of bile canaliculus and fibrous tissue at portal area(up arrow), also coagulation necrosis and karyopyknosis of hepatocytes could be seen. Original magnification × 400. (C, D) Showing proliferation of connective tissue between liver lobule (arrow). Mallory staining method, Original magnifications ×200. (A, C: liver sample from CP74; B, D: liver sample from DX385).

Figure 3

Immunohistochemical analysis of HBsAg and HBcAg in liver tissues.(A) Strong HBsAg immune positivity was shown in hepatocytes (arrow). (B) Immunopositivity for HBsAg was mainly distributed in cytoplasm of hepatocytes. (C, D) HBcAg was distributed mainly distributed nucleus of hepatocytes. Spotty parenchymal cell degeneration, with necrosis and karyopyknosis (arrow) of hepatocytes were observed. Original magnification×400. (A, C: liver sample from CP74; B, D: liver sample from DX385).

Figure 4

Viral particles in swine sera and hepatocytes revealed by electron microscopy. A: Electron micrographs of negatively stained SHBV particles from HBsAg positive serum. Two types of particles were observed which are similar in size (20 nm and 40 nm) and morphology, like complete and empty viral particles of SHBV. B: Virus-like particles in the nucleus of hepatocytes (liver sample from DX385).