Genotype A HBV mapped in acute, chronic Japanese patients

By Shreeya Nanda, Senior medwireNews Reporter

Not only is genotype A the most common genotype among Japanese patients with acute hepatitis B virus (HBV) infection, but its prevalence is spreading among young adults with chronic HBV infection, shows a nationwide study.

Between 2005 and 2010, 46.7% of 552 acute HBV patients were infected with genotype A virus while 39.7% and 11.8% had HBV of genotype C and B, respectively.

Patients with genotype A were significantly younger (p=0.0008), had a lower peak level of alanine aminotransferase (ALT; p=0.0052) and a longer duration until clearance of hepatitis B surface antigen (p<0.00001) than their non-genotype A counterparts.

Among 3619 patients with chronic HBV recruited between 2010 and 2011, genotype C was the predominant genotype, with an incidence of 77.6%, followed by genotypes B, A and D at 17.5%, 4.1% and 0.6%, respectively.

But the incidence of genotype A was “relatively high” among younger patients, says the team, with a prevalence of 11.1%, 12.9% and 8.6% in the 19 years and under, 20 to 24 and 25 to 29 year age groups, respectively.

Researcher Masashi Mizokami, from the National Center for Global Health and Medicine in Ichikawa, Japan, and colleagues also point out that the overall prevalence of 4.1% was significantly higher than the 1.7% nationwide incidence observed between 2000 and 2001 (p<0.001), but comparable to the 3.5% prevalence in the 2005 to 2006 period. They add that this trend in the rise of genotype A “requires verification in future nationwide surveys”.

Chronic HBV patients with genotype A were significantly younger than those with genotypes B and C (p<0.0001), although patients with genotype D were the youngest. And the genotype A group had a significantly higher proportion of men than the other genotypes (p=0.014).

Moreover, the percentage of patients with HIV co-infection was significantly greater for genotype A than for the other genotypes in both acute (p<0.0001) and chronic (p<0.0001) patients, which the researchers say could be because genotype A HBV and HIV have similar routes of transmission.

Noting that genotype A HBV is a “much more common” cause of acute disease in Japan than would be expected from the relative incidence in chronic HBV patients, they speculate in the Journal of Gastroenterology and Hepatology: “Because genotype A induces milder hepatitis, which is characterized by a lower peak ALT level and associated with weaker cellular immune responses, genotype A may spread unknowingly by sexual routes.”

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