Enterovirus 71: the virus, its infections and outbreaks

Enterovirus 71 (EV71) was first recognized in 1974. Since then it has been implicated in 13 small and large outbreaks world-wide. Large outbreaks of hand, foot and mouth disease (HFMD), mostly benign, occurred in Japan in 1973 and 1978. Four outbreaks with brain stem encephalitis and significant numbers of deaths occurred in Bulgaria and Hungary in the late 1970's and in Malaysia and Taiwan in 1997 and 1998 respectively. During the latter two epidemics, pulmonary edema and hemorrhage often leading to quick deaths in children aged from 0.5 to 3 years old was first recognized. In Taiwan 78 deaths and over 100,000 cases of HFMD occurred. Coxsackie A16 cocirculated with EV 71, without however, causing any severe illnesses. The transmission of EV 71 was related to number of siblings in a household, rural residence and contact with cases of HFMD. Genotype analyses show that genotypes have changed with time in the United States and Japan. Recent isolates from Japan are similar to the isolates from Malaysia and Taiwan in 1997 and 1998, respectively. Even though genotype analysis has not identified specific sequences responsible for neurovirulence, the strains causing brain stem encephalitis and pulmonary edema in the Far East are similar and have arisen since 1997. Seroepidemiological studies in Taiwan suggest that children aged from 0.5 to 4 years old are most susceptible while the rest of the population are over 50% immune. Theoretically there is a pool of such susceptible subjects every few years. In prevention for another major outbreak, a simple, inactivated Salk type vaccine should be immediately prepared and made available.