The EH 24/70 virus, now identified as an antigenic variant of coxsackievirus type A24 in tube neutralization and immunodiffusion tests, was found to be the etiological agent of the 1970 outbreak of acute conjunctivitis in Singapore. The following year, strains identical to EH 24/70 virus were isolated in Hong Kong from a number of patients with acute conjunctivitis. Thus EH 24/70 virus seems to be the first human enterovirus incriminated in a large outbreak with acute conjunctivitis as the dominant clinical feature. Serologic responses substantiated the causative role of EH 24/70 virus in human disease. Human conjunctiva was not the sole habitat of the EH 24/70 virus, as it was also readily isolated from throat washings of patients in the acute phase of illness.

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The evolution of the variant of Coxsackievirus A 24 (CA 24 v) which causes acute hemorrhagic conjunctivitis was explored. Using 15 isolates obtained from Southeast Asia during the period 1970-1986, the genetic distance between isolates was estimated from pairwise comparison of nucleotide changes deduced from common spots on oligonucleotide maps of the isolates. From regression analysis of the genetic distance and the time of isolation of the isolates, the evolutionary rate of CA 24 v was estimated to be 3.44 x 10(-4)/nucleotide/month. The phylogenetic relationship of these isolates was explored using the neighbor-joining method and the modified unweighted pair group method using arithmetic averages (UPGMA). The phylogenetic tree constructed indicates that CA 24 v appeared from one focal place in July 1968 +/- 25 months, very close to the time of the first world epidemic of, then newly recognized, acute hemorrhagic conjunctivitis.

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