Serotype-specific antigen ELISA for detection of Chiba virus in stools

Chiba virus (CV), a Norwalk‐like virus (NLV), was first identified as a cause of oyster‐associated outbreak of gastroenteritis that occurred in Chiba prefecture, Japan, in 1987. An enzyme‐linked immunosorbent assay (ELISA), based on hyperimmune antisera to recombinant baculovirus‐expressed capsid proteins of CV (rCV), was developed to detect CV antigen in stools. No cross‐reactions were observed with other enteric viruses including enteroviruses, rotaviruses, astroviruses, or enteric adenoviruses. The ELISA was used to screen 101 stools collected from 16 oyster‐associated outbreaks of acute gastroenteritis. Twelve stools (11.9%) from seven outbreaks were positive for CV antigen. Ten rCV ELISA‐positive strains were confirmed by RT‐PCR and nucleotide sequencing. ELISA‐positive strains showed 96–100% nucleotide sequence identity to each other, though they were obtained nine years apart. Phylogenetic analysis demonstrated that all ten strains clustered with the prototype CV in genogroup I viruses. We concluded that the antigen ELISA described in this study is highly type‐specific, and that this method should be useful for epidemiological surveys of Chiba virus infections. J. Med. Virol. 62:233–238, 2000. © 2000 Wiley‐Liss, Inc.