Hepatitis B Virus Discovered in Donkeys and Zebras

The discovery of a previously unknown hepatitis B virus in donkeys and zebras opens up new opportunities for understanding the progression of the disease. Until now, the lack of an animal model for studying this chronic condition in humans had slowed the development of targeted treatments.   In France, 300,000 people have chronic hepatitis B, a disease responsible for the deaths of more than 800,000 people worldwide each year. The high number of chronic cases is particularly problematic for global public health, and to date, no therapeutic options are in sight. There is an urgent need for treatments, but their development is hampered by the lack of suitable animal models. A recent discovery could be a game-changer. German researchers have, for the first time, described a virus related to the hepatitis B virus (HBV) in donkeys and zebras, which is believed to have emerged in Africa at the time of the domestication of these equines, several thousand years ago. Molecular, histopathological, and biochemical analyses have revealed that the infection patterns of this equine HBV resemble those observed in humans, including moderate liver lesions, progressive stasis, and potential horizontal transmission of the virus. It causes a hepatotropic disease comparable to the human infection and prolonged symptoms resembling the chronic hepatitis B that affects humans. However, the two viruses are not exactly identical. Equid HBV is, in fact, unable to infect human liver cells. This discovery comes five years after the identification, also in donkeys, of viruses genetically related to the human hepatitis C virus (HCV). Given that humans are often co-infected with HCV and HBV, the researchers undertook extensive serological, histopathological, epidemiological, and molecular biology studies to identify the hepatitis B virus in animals. They analyzed nearly 3,000 samples from equines (donkeys, zebras, and horses) across five continents. Ultimately, 3.2% of the donkeys and zebras tested by PCR tested positive for the new virus, and antibodies against Equid HBV were detected in 5.4% of the animals. Antibodies against Equid HCV were also detected in 26.5% of donkeys that were seropositive for Equid HBV, confirming susceptibility to both hepatitis viruses. In vitro infection studies suggest that horses are also susceptible to the new virus. The discovery of Equid HBV thus offers a unique opportunity to study chronic hepatitis B in vivo, to understand the progression of the disease, and thereby to mitigate or prevent its severe clinical manifestations. This research also paves the way for preclinical animal trials aimed at identifying new therapeutic solutions against HBV that could benefit both humans and animals. It is now also possible to study HBV/HCV interactions during coinfection, with the goal of better understanding the pathogenesis with a view to potential therapeutic optimization.