Genetic variation of capsid protein VP7 in genotype g4 human rotavirus strains: simultaneous emergence and spread of different lineages in Argentina

Abstract

Rotavirus is the most-common cause of severe diarrhea in young children. Complete rotavirus characterization includes determination of the antigenic type of the two outer capsid proteins, VP7 and VP4, designated G and P types, respectively. During a nationwide rotavirus surveillance study, genotype G4 frequency increased during the second year. To evaluate further the mechanism of emergence and the relationship among G4 strains, the genetic diversity of VP7 capsid protein in these samples was studied in detail. Overall nucleotide sequence divergence ranged from less than 0.1 to 19.5%, a higher divergence than that observed for other rotavirus G types (0.1 to 9%). Sequences were classified into two major lineages (designated I and II) based on their nucleotide distances. The most heterogeneous lineage was further subdivided into four sublineages (designated Ia to Id). Most Argentine sequences were of sublineages Ib and Ic, which were confirmed to be independent sequence clusters by parsimony analysis. This study describes different lineages and sublineages within G4 strains and shows that Argentine strains are distantly related to reference strain ST3. The appearance of at least two G4 genotype (sub)lineages during 1998 demonstrates that the increased frequency of these strains was due to the synchronized emergence of different groups of strains.

FIG. 1.

Phylogenetic analysis of VP7 nucleotide sequences of genotype G4 strains. A phylogenetic tree was constructed using the Kimura and Neighbor-Joining programs of the PHYLIP package. Argentine strains and dates of collection (month/year) of the sample are in boldface type. Percentage bootstrap values above 60% are shown at the branch nodes. Abbreviations for locations: Jap, Japan; Aus, Australia; SA, South Africa; It, Italy; SF, Santa Fe; Tuc, Tucumán; Men, Mendoza; Ros, Rosario; BA, Buenos Aires; Res, Resistencia; LP, La Plata; Cor, Cordoba; Mis, Misiones; Ush, Ushuaia.

FIG. 2.

Deduced amino acid sequences of G4 strains compared to sequence of reference strain ST3. Underlined amino acids indicate regions that are highly variable among G types. Antigenic regions are boxed and marked as A, B, and C, respectively.

FIG. 2.

Deduced amino acid sequences of G4 strains compared to sequence of reference strain ST3. Underlined amino acids indicate regions that are highly variable among G types. Antigenic regions are boxed and marked as A, B, and C, respectively.