Sequence diversity of human caliciviruses recovered from children with diarrhea in Mendoza, Argentina, 1995-1998.

Human caliciviruses were detected by EIA and/or RT-PCR in stool specimens from children with diarrhea treated at out- or in-patient facilities between 1995 and 1998 in Mendoza, Argentina. Mexico virus-like strains detected by primers NV36/51 were transiently prevalent in 1995/1996. Significantly more human caliciviruses were detected when primers were designed from contemporaneously circulating strains. Nucleotide sequences of a highly conserved region in the RNA polymerase gene of 10 selected human caliciviruses were determined. Eight strains were Norwalk-like viruses and two strains were Sapporo-like viruses. Seven of the eight Norwalk-like viruses also were positive by the recombinant Mexico virus antigen EIA. The seven Mexico virus EIA-positive strains revealed two patterns in the RNA polymerase sequences: two strains were closest to Mexico virus and the other five strains were closest to Lordsdale virus. One of the five "Lordsdale" viruses was found to be a naturally occurring recombinant between the Mexico virus and Lordsdale human calicivirus genetic clusters [Jiang et al., (1999b) Archives of Virology 144:2377-2387]. The Mexico virus EIA-negative strain had 73-77% nucleotide identity with the closest related Norwalk-like viruses, indicating it might belong to a new genetic cluster of the Norwalk-like virus genus. The two Sapporo-like viruses were distinct genetically; one belonged to the Houston/90 or Parkville cluster and the other to a new cluster. Some strains appeared to have short periods of prevalence and locally adapted primer pairs significantly increased detection rates. The finding of high diversity of circulating strains, including recombinant strains and strains with previously unrecognized genetic identities, highlights a need for studies of human caliciviruses in these children and other populations.