The discovery of a previously unknown hepatitis B virus in donkeys and zebras opens up new opportunities for understanding the course of the disease, according to researchers.
Hepatitis B virus infections are among the major global health problems in humans. Particularly problematic is the high number of chronic courses of the disease, causing the deaths of more than 800,000 people globally every year.
So far, there is no therapy to cure the condition.
The discovery of the virus is reported in the Proceedings of the National Academy of Sciences.
“With the discovery of a new hepatitis B virus in donkeys and zebras capable of causing prolonged infections, we now have the opportunity for a better understanding of the chronic course of the disease and thus also for mitigation or prevention of severe clinical consequences,” said Professor Jan Felix Drexler, a researcher with German Center for Infection Research at the Charité – University Medicine Berlin, which is one of the largest university hospitals in Europe.
In his role with the center, Dr Drexler identifies and characterizes emerging viruses that could be dangerous for humans. This does not appear to be the case with the recently discovered virus.
“Five years ago we were able to show for the first time that donkeys harbor viruses that are genetically related to the human hepatitis C virus,” explained Andrea Rasche, lead author of the study, who also works for the infection research center at the hospital.
Since hepatitis C virus and hepatitis C virus often occur together in humans, the researchers have also searched for hepatitis b virus worldwide in donkeys. In addition to field work, extensive molecular, serological, histopathological and evolutionary biology methods were used.
“We have studied nearly 3000 samples from equids, i.e. from donkeys, zebras and horses in five continents, and we found that donkeys are global carriers of the new hepatitis B virus,” Drexler said.
Its origins could be linked to the domestication of donkeys in Africa a few thousand years ago.
Donkeys can be naturally infected with hepatitis B virus as well as with hepatitis C. Zebras can also become infected with hepatitis B virus; horses are also likely to be receptive, but in initial studies, the scientists could not confirm any naturally infected horses.
In naturally infected donkeys, the course of the infection is similar to chronic hepatitis B in humans.
“The new hepatitis B virus appears to use an unknown receptor for entry into the host cell,” explained Felix Lehmann, second lead author of the study and a scientist with the German Center for Infection Research at Giessen University, where he studied the molecular biology of virus binding and entry in cell culture.
The emergence of human hepatitis B virus and the development of its receptor use remain unclear and are being jointly investigated by the researchers from Berlin and Giessen.
“Since the virus is unable to infect human liver cells, human infection with this virus can be ruled out with a high degree of probability,” emphasises Professor Dieter Glebe, who heads the National Reference Centre for Hepatitis B and D viruses at Giessen University, and is also a scientist in the hepatitis research unit at the German Center for Infection Research.
The scientists are convinced that with the virus in donkeys and zebras, they can develop a better understanding of the pathogenesis of chronic hepatitis B and of hepatitis B and C co-infection to lay a foundation for new therapies.
A hepatitis B virus causes chronic infections in equids worldwide
Andrea Rasche, Felix Lehmann, Nora Goldmann, Michael Nagel, Andres Moreira-Soto, Daniel Nobach, Ianei de Oliveira Carneiro, Nikolaus Osterrieder, Alex D. Greenwood, Eike Steinmann, Alexander N. Lukashev, Gerhard Schuler, Dieter Glebe, Jan Felix Drexler, the Equid HBV Consortium
Proceedings of the National Academy of Sciences Mar 2021, 118 (13) e2013982118; DOI: 10.1073/pnas.2013982118