Molecular epidemiology of hepatitis A, B and C in Estonia

Abstract

During the last decade changes have occurred in the epidemiology of hepatitis A, B and C in Estonia. A shift from high to intermediate endemicity for hepatitis A has led to a shift in age of susceptible individuals from children to adolescents and adults. A dramatic increase in injecting drug use (IDU) in the population aged 15-29 years in the mid 90s has led to an increased incidence for both hepatitis B and C. Since there was little information on genotypes of the viral hepatitides in Estonia, our aim was to characterize Estonian strains of these viruses and assess their relatedness to such strains from other parts of the world.

In 1998-1999 a small group of IDUs became the source for a community-wide outbreak of hepatitis A in Estonia. 107 anti-IgM hepatitis A virus (HAV) positive sera sampled from hospitalised patients during the outbreak in 1998-1999 and 68 sera collected before and after the outbreak were used as source of HAV RNA for characterization of the viral VP1 region. All strains from 1998-1999 belonged to subtype IIIA, a subtype previously linked to IDU in other countries, while the background strains belonged to subtype IA. The IA strains formed two discrete clades distinct from hepatitis A strains from other parts of the world. Despite subtype IA of HAV has been dominating in Estonia during 1994-2001, the outbreak in 1998-1999 was due to subtype IIIA. This study provides further proof for the use of sera and VP1 sequencing for investigating the molecular epidemiology of hepatitis A.

For genotyping of hepatitis B virus (HBV) in Estonia and other regions of the former USSR HBsAg positive sera collected during 1989-2002 were investigated. By sequencing 530 S-genes three genotypes D (81%), A (18.5%) and C (0.5%) were identified. To characterize their subgenotypes complete genomes were sequenced for 13 genotype A and 33 D strains. All genotype A strains belonged to subgenotype A2. The D strains segregated into subgenotypes D1, D2 and D3 where D2 was dominating. All genotype A strains encoded adw2. The D1 and D3 strains all encoded ayw2, while the D2 strains encoded ayw3, ayw4 and adw3 subtypes. Strains from Estonia mostly belonged to D2 as did strains from Siberia, while strains from Central Russia were mostly D3. Despite there was a relatively low divergence between the subgenotypes of D, they were characterized by specific combinations of amino acid substitutions in the Pol and S-gene products. A number of clades formed by strains collected in distantly located regions were composed by strains with identical S-gene sequences, which were shown to be monophyletic at the level of complete genomes and formed subclades according to geographical origin. The rather low nucleotide divergence may indicate past iatrogenic spread of HBV the region.

For the characterization of hepatitis C virus (HCV) 353 anti-HCV positive sera collected in Estonia during 1996-2004 from health care workers, blood donors and hospitalized patients were investigated by phylogenetic analysis within the 5 UTR core and NS5B regions. Subtype 1b was most prevalent (71 %) followed by 3a (24%), 2c (2%), 1a (1%) and 2a (1%). One patient was infected with the 2k/1b recombinant. Relative changes in distribution of subtypes 1b and 3a was observed during the study period, and a shift from 1b to 3a partially coinciding with the hepatitis A outbreak in IDUs with further replacement of 3a with 1b. Estonian 1b strains were similar to strains published from different regions of the former USSR. However, for 3a there seemed to be two separate introductions into Estonia. Subtypes1b and 3a seemed to co-circulate in the community independent from risk factors.

In general the genotypes of viral hepatitides in Estonia were those characteristic for a Western country with IA for HAV, A and D for HBV and 1b and 3a for HCV, the former the indigeneos subtype of Eastern Europe and the latter reflecting IDU mediated introductions into the country.