Evidence of high-frequency genomic reassortment of group A rotavirus strains in Bangladesh: emergence of type G9 in 1995.

We characterized 1,534 rotavirus (RV) strains collected in Bangladesh from 1992 to 1997 to assess temporal changes in G type and to study the most common G and P types using reverse transcription-PCR, oligonucleotide probe hybridization, and monoclonal antibody-based enzyme immunoassay. Results from this study combined with our previous findings from 1987 to 1991 (F. Bingnan et al., J. Clin. Microbiol. 29:862-868, 1991, and L. E. Unicomb et al., Arch. Virol. 132:201-208, 1993) (n = 2,515 fecal specimens) demonstrated that the distribution of the four major G types varied from year to year, types G1 to G4 constituted 51% of all strains tested (n = 1,364), and type G4 was the most prevalent type (22%), followed by type G2 (17%). Of 351 strains tested for both G and P types, three globally common types, type P[8], G1, type P[4], G2, and type P[8], G4, comprised 45% (n = 159) of the strains, although eight other strains were circulating during the study period. Mixed G and/or P types were found in 23% (n = 79) of the samples tested. Type G9 RVs that were genotype P[6] and P[8] with both long and short electrophoretic patterns emerged in 1995. The finding of five different genotypes among G9 strains, of which three were frequently detected, suggests that they may have an unusual propensity for reassortment that exceeds that found among the common G types. We also detected antigenic changes in serotypes G2 and G4 over time, as indicated by the loss of reactivity with standard typing monoclonal antibodies. Our data suggest that a vaccine must provide protection against type G9 RVs as well as against the four major G types because G9 strains constituted 16% (n = 56) of the typeable RV strains and have predominated since 1996.