MOLECULAR EPIDEMIOLOGY OF A VARIANT OF COXSACKIEVIRUS-A24 IN TAIWAN -2 EPIDEMICS CAUSED BY PHYLOGENETICALLY DISTINCT VIRUSES FROM 1985 TO 1989

In order to know the phylogenetic relationship and the route of transm ission of a variant of coxsackievirus A24 (CA24v), an agent that cause d four sequential outbreaks of acute hemorrhagic conjunctivitis from 1 985 to 1989 in Taiwan, the nucleotide sequence variations in the virus -encoded proteinase 3C region (549 nucleotides) were studied with 19 i solates. The prototype strain (EH24/70), four isolates from Japan, and two isolates from Hong Kong were used for comparison. The nucleotide sequences of the Taiwan strains from the 1985-1986 and 1988-1989 epide mics were closely related within each epidemic, while they were more d istantly related between strains from two epidemics. Phylogenetic anal ysis by the unweighted pairwise grouping method of the arithmetic aver age revealed that the 19 Taiwan isolates had diverged into two groups, 1985-1986 and 1988-1989 groups. The time at which these two groups di verged was estimated to be around May 1982, more than 3 years prior to the first appearance of the CA24v epidemic in Taiwan. On each occasio n, the viruses caused a 2-year epidemic and then disappeared. The Taiw an isolates from 1985 to 1986 were closely related to the Japan isolat es from 1985 to 1986 and the Taiwan isolates from 1988 to 1989 were ph ylogenetically close to the 1989 Japan isolates, indicating that Taiwa n and Japan had two common-source outbreaks. However, none of the 1988 Taiwan isolates were phylogenetically close to the 1988 Japan or Hong Kong isolates. The evidence revealed that Taiwan has had two repeated but discontinuous introductions of CA24v since its first appearance i n Taiwan in 1985. None of the other CA24v strains have been detected s o far.