Hepatitis B: Unusual virus discovered in shrews
The discovery of an unusual hepatitis B virus from shrews offers new opportunities to better understand the chronic progression of the disease. International research teams have been able to demonstrate that an important protein, essential for the development of chronic infection, is not present in this virus. Scientists from the DZIF of the Charite-Universitaetsmedizin Berlin and the University of Giessen lead the research.
Hepatitis B virus (HBV) infection is one of the major global health problems. The high number of chronic cases is particularly problematic: More than 240 million people worldwide are chronically infected with this virus and more than 887,000 of them die each year from long-term consequences of this disease, such as cirrhosis and liver cancer. The chronification of HBV infection, which often goes unnoticed for decades, is one of the fundamental characteristics of this virus. "The discovery of this unusual HBV in shrews gives us an opportunity to better understand the pathogenesis of this chronic disease," says lead author of the study Andrea Rasche, a scientist at Charite-University Medicine Berlin and a DZIF Maternity Leave grant holder.
An important protein necessary for the chronification of infection is not present in the virus in shrews. "Jan Felix Drexler, DZIF researcher at Charite-University Medicine Berlin and DZIF researcher in the field of "Emerging Infections" research. And this applies to all known HBVs in mammals. They form this protein during infection. This immunomodulator suppresses the body's specific immune response to HBV so that the infection cannot heal and becomes chronic - often with very high viral concentrations in the blood. When this viral protein is not present, the body's immune system can successfully fight the infection.
This is not the case with the newly discovered HBV in shrews. The researchers examined nearly 700 shrew samples from Europe and Africa and despite the absence of HBeAg, infected animals still had high levels of HBV in their blood. "Dieter Glebe, Director of the National Reference Centre for Hepatitis B and D Viruses at Justus Liebig University Giessen (JLU) and DZIF researcher in the field of "Hepatitis" research. "Since the virus cannot infect human liver cells, it is very unlikely that the virus can infect humans." Therefore, it is reasonable to conclude that there is no risk to humans if they come into contact with HBV-infected shrews.
Another feature of the newly discovered virus is that it does not use the liver's bile acid transporter to enter liver cells as is the case with HBV in humans and monkeys, but takes an unknown path in the cell. "This shows that we do not yet know all the HBV receptor molecules," explains Professor Drexler. In addition to these important findings on HBV infection, the shrew virus gives us a new insight into the genealogy of HBV. "Our evolutionary studies show that HBV has existed in mammals for millions of years, probably around 80 million years," says Professor Drexler.
Scientists now want to examine in more detail the unusual pattern of HBV infection in shrews that develops without the HBeAg central immunomodulator. Despite intensive international efforts, effective treatment of chronic hepatitis B has not yet been developed. One reason is that there are no appropriate animal models that can be used to examine the complex interactions of viral infection with the host's immune system. "Shrews could be a promising animal model for HBV research. The virus discovered here is particularly suitable for examining the mechanisms of chronic HBV infections," explains Professor Drexler.
