Isolation and characterization of mumps virus strains in a mumps outbreak with a high incidence of aseptic meningitis

In 1993, mumps with a high incidence of aseptic meningitis became prevalent in Akita prefecture, Japan. Three mumps virus isolates obtained from the nonvaccine-associated cases lacked the BamHI restriction cleavage site of the P gene, like the Urabe strain (Yamada, A. et al, Vaccine 8: 553-557). However, four additional nucleotide substitutions were found in the determined region of 157 bp. Fourteen of 19 cases from which mumps virus showing the Urabe-like RFLP profile was detected were complicated with symptomatic meningitis, whereas there were only four cases of meningitis among 23 individuals infected with the wild type showing no Urabe-like RFLP profile (non-''Urabe-like'' wild-type). The incidence of meningitis was over 70% among patients infected with the ''Urabe-like'' wild-type virus. The ''Urabe-like'' wild-type disappeared after February 1994 in the epidemic area and was replaced by the non-''Urabe-like'' wild-type. Patients infected with the ''Urabe-like'' wild-type lived in a closed colony, in which there were two instances of transmission between siblings. Thus this outbreak was transient and narrowly localized.