A window into the past
The hepatitis B virus (HBV) causes potentially life-threatening diseases, including cirrhosis and liver cancer. The virus is transmitted by bodily fluids and is thought to infect around two billion people, causing approximately 600 000 deaths a year.
HBV has at least ten genotypes. Each genotype, which refers to the arrangement of genetic material in a virus, is divided into multiple subgenotypes, each localised to a particular area or population.
In Korea, where HBV infection is endemic, most viruses isolated are from the C2 (HBV/C2) genotype. The big question is, ‘Where did HBV/C2 come from?’ Now, remarkably, a 16th-century mummy is helping scientists solve the mystery.
The extremely well-preserved mummy – a child who was between four and six years old when he died – was discovered in 2007 in Korea. Researchers managed to identify and extract samples from the mummy’s liver, which were sent to three laboratories around the world for analysis.
Although the DNA was degraded, the researchers were able to reconstruct the sequence of the ancient HBV (aHBV) DNA and compare it with known HBV sequences from different geographical locations. The aHBV is substantially different to HBV/C1 sequences from Thailand, Vietnam and Myanmar but is similar to HBV/C2 sequences from Korea, Japan and China. The differences in the DNA of these viruses might be the result of spontaneous DNA mutations, or they might have resulted from mutations following evolutionary pressures, such as the human immune response.
Using estimations of DNA mutation rates, the authors suggest that the aHBV is between 3000 and 100,000 years old – a big time window – and probably originated in China or Japan, before spreading to Korea via human migration. This study is remarkable because aHBV is the oldest complete viral genome to be reconstructed and only the second ancient viral genome that has been described (the other is the 1918 Spanish influenza virus).
Sruthi is a freelance science writer
Bar-Gal GK, Kim MJ, Klein A, Shin DH, Oh CS, Kim JW, Kim TH, Kim SB, Grant PR, Pappo O, Spigelman M, Shouval D. (2012). Tracing hepatitis B virus to the 16th century in a Korean mummy Hepatology DOI: 10.1002/hep.25852