STUDY OF NORWALK-RELATED VIRUSES IN MEXICAN CHILDREN

Two-hundred Mexican children monitored from birth to 2 years of age in a cohort study of diarrhea were tested for Norwalk virus (NV) and Nor walk-related virus infection. Blood was collected quarterly and tested by an enzyme immunoassay (EIA) using the recombinant NV (rNV) particl es as antigen. Stool was collected weekly and tested by an EIA using h yperimmune anti-sera from animals immunized with rNV and a reverse tra nscription-polymerase chain reaction (RT-PCR) with primers in the RNA polymerase region of NV. A high prevalence of serum antibody to NV (85 % at age 2 years) was found by the antibody EIA. In 54 stool specimens selected from children who developed a high titer of serum antibody t o rNV, none was positive for NV by the antigen EIA, but 6 yielded prod ucts by the RT-PCR. One stool specimen (MX virus) yielded a 3.3 kb RT- PCR product from the 3' end of the viral genome. The MX virus cDNA has a genomic organization like other caliciviruses. Sequence comparison showed that MX virus shares 80% nucleic acid and 91% amino acid sequen ce identity with Snow Mountain agent (SMA), but only 62% and 60% ident ity, respectively, with NV in the RNA polymerase region, suggesting th at MX virus is a SMA-like virus. (C) 1995 Wiley-Liss, Inc.