Hepatitis B and hepatitis C virus in Lao blood donors

Hepatitis B virus (HBV) is highly endemic in the Lao People’s Democratic Republic. In collaboration with the Lao Red Cros, the Institute of Immunology, Luxembourg has shown that approximately 45.5% of Lao blood donors are positive for at least one hepatitis B virus serum marker; anti-HBs, anti-HBc or HBsAg, suggesting that almost half have been previously exposed to HBV. 9.6% of donors were screened out of the blood donation process, due to HBsAg positivity, indicating a high prevalence of chronic infection).
Furthermore, a large variety of subgenotypes (B1, B2, B4, C1, C5, I1, I2) are present in HBsAg positive donors with subgenotypes B4 and C1 dominating. Mixed genotype infections are also common and found in up to 6% of HBsAg positive donors, with approximately 65% of these infections having recent recombinations within the S-gene alone. These mixed and recombinant infections are highly variable but have not yet led to new dominant strains within the studied population. In more than 30% of donors with recombinant strains, the most closely related known virus was found in the same donor, suggesting recent recombination events. Importantly, two new subgenotypes (I1 and I2) have been identified and characterised, belonging to a recently defined genotype I and representing up to 5% of HBV infections. Molecular analyses suggested that this genotype developed outside Southeast Asia in the distant past by a series of recombinations. Importantly, 3.9% of blood donations were HBsAg negative but DNA positive (occult infected) and potentially infective for HBV. This has implications for the HBV screening of Lao blood donations, which are currently tested only for HBsAg but not DNA.
Other previous work from the Institute of Immunology in Luxembourg, in collaboration with the Lao Red Cross, examined the molecular epidemiology of hepatitis C virus (HCV) from anti-HCV-positive first-time blood donors. Out of 105 samples, forty-five were positive for HCV (42.9%); two belonged to subtype 1b (2/45, 4.4%) and all others to genotype 6 (43/45, 95.6%), including subtypes 6b, 6h, 6k, 6l, 6n and 6q. Three groups of sequences were not clearly attributable to any genotype 6 subtype, two of which may be regarded as candidates for new subtypes of genotype 6. Two samples were mixed infected with different subtypes or clusters of genotype 6 viruses.
The LaoLux laboratory continues to work in close collaboration with the Lao Red Cross and the Institute of Immunology, to further investigate the prevalence and molecular characteristics of hepatitis infections in Lao blood donors. Current investigations include nationwide surveys of the prevalence of occult HBV infections, the incidence of hepatitis D co-infection with HBV and the infectivity of HBV occult infected blood. These studies are an important contribution to the safety of blood recipients and the epidemiology of hepatitis B and C in the young Lao population.