Hepatitis B origin revealed in DNA of bird fossils

The ancient ancestor of the human Hepatitis B virus has been discovered by a team of scientists from the University of Münster, and is 63 million years older than previous estimates stated. Found in fossilised songbird genomes, scientists hope that the genetic information will help tackle the modern day human Hepatitis B virus.

Hepatitis B virus (HBV) is a viral infection of the liver which causes severe flu-like symptoms, and while most HBV infections resolve themselves quickly about 20% of cases are chronic. Of the chronic cases, lasting over six months, 15 to 40% develop cirrhosis, various liver diseases or liver cancer. HBV is also responsible for up to 80% of all hepatocelluar carcinomas worldwide.

The new field of study which researches fossil virus DNA, and found the 82 million years old Hepatitis Virus, is called palaeovirology. It uses viral fossils, which are fragment of ancient viral DNA whose evolution is stunted as soon as they become trapped within the germline of their hosts. These fossils therefore are the key to studying viral sequences that are millions of years old.

Palaeovirology has dated this HBV back in avian DNA as far as the age of the dinosaurs in the Late Mesozoic; however when mammals became involved is still up for speculation.

“HBVs have probably been infecting mammals for a much shorter time than they have been infecting birds throughout much of their evolution,” said Dr Suh from the study.

However the ancient HBV is surprisingly similar to that of modern day, and even with 82 million years of evolution the proteins have stayed the same. The only difference between the ancient avian HBV and the modern mammalian HBV is an extra protein in the modern HBV known as the X protein. This X protein is required for HBV replication in mammals, and may be the reason that the HBV lineage switched hosts from avian to mammalian.

These findings, which the scientists call “the tip of the iceberg of prehistoric virus genomes”, will expand our understanding of HBV and most importantly may improve its treatment in humans.