A Case of Enterovirus Outbreak: Enterovirus 71

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Enterovirus 71 was first isolated in 1969. Since then it has been associated with sporadic cases of outbreaks in various parts of the world, including the U.S., Brazil, Europe, Austrailia, Malaysia, and Taiwan. Entervirus 71 infection may present itself much like other enterovirus infections, with symptoms ranging from asymptomatic to the presentation of rashes, diarrhea, colds, meningitis, encephalitis, hand-foot-mouth disease, myocarditis, or some combination of these syndromes. On the other hand, Enterovirus 71 may cause many unusal syndromes such as acute flaccid paralysis (similar to paralytic poliomyelitis), bulbar and brain encephalitis, Guillain-Barre syndrome, and rapidly fatal pulmonary edema and hemmorrhage.

Recent outbreaks of Enterovirus 71 which have caused death have occurred in Malaysia in 1997 and in Taiwan in 1998. The outbreak in Taiwan was very large. From March to December 1998, 129,106 cases of hand-foot-mouth disease and herpangina were reported by sentinel physicians. Assuming though that the number of reported cases only represents a fraction of the number of actual cases, it is possible that as many as 1,483,977 cases may have occurred in Taiwan. Of the reported number of cases, 61.9 percent were attributed to enterovirus 71, with the other cases being attributed to Coxsackievirus A16 and other enteroviruses. Severe disease was reported in 405 patients, most occuring in children less than 15 years of age. Among the severe cases, 19.3 percent were fatal. All of the fatal cases were associated with enterovirus 71, and all occurred in children less than 5 years of age.

The association of Enterovirus 71 with fatal cases was based on autopsy which revealed the presence of Enterovirus 71 in the spinal cord and medulla of a fatal case. When children went to the hospital with a serious case, many had a high fever for 2-4 days and then suddenly their condition worsened and the children died within 12-24 hours. Most of the patients who died in the Taiwan outbreak had hand-foot-mouth disease or herpangina and died of pulmonary edema and hemorrhage or after they developed brain-stem encephalitis.

The Taiwan outbreak brings out several questions. First of all, what was the precise mode of transmission? Enteroviruses are usually transmitted by fecal-oral route, but the pattern of spread in this epidemic suggests repiratory transmission. Secondly, Enterovirus 71 has been known to cause infections in Taiwan before this deadly outbreak. Thus, why wasn't the Taiwan population more immune to this particular strain? Was this a particularly virulent strain of Enterovirus 71? If so, what made it so virulent? One interesting theory to explain this situation is that the Taiwanese people may have had hypersensitivity to Enterovirus 71 when they were concurrently or previously infected with Coxsackievirus A16. If this were the case, then the outcome would be much like the outcome superinfection of dengue virus in a patient who has already been infected with another dengue virus strain: the patient may develop dengue shock and hemorrhagic syndrome.

What is for sure though, is that clinicians and epidemiologists throughout the world, need to be aware of the capacity of Enterovirus 71 to cause large epidemics which may lead to death.