Correspondence

Outbreaks of Enterovirus 71 Infection

N Engl J Med 2000; 342:355-356February 3, 2000

Article

To the Editor:

The outbreak of enterovirus 71 infection in Taiwan, reported by Ho et al. (Sept. 23 issue),1 occurred almost a year after the outbreak in Malaysia. Though both outbreaks occurred in Asia and both involved large numbers of deaths, it was not known whether the two outbreaks were related. We studied the nucleotide sequence and secondary RNA structure of some of the isolates, using the sequence of the 5' untranslated region (UTR).

Enterovirus 71 isolates from patients in Singapore (seven isolates), Taiwan (two isolates), and Japan (one isolate) were examined and compared with those previously reported in Malaysia2,3 or with sequences deposited in GenBank. A phylogenetic tree that we constructed using the aligned 5' UTR sequences revealed at least two major clusters of enterovirus 71 isolates. Cluster 1 included the isolate from Japan and six of the seven isolates from Singapore, together with isolates found predominantly in Malaysia during the 1997 outbreak. The isolates in this cluster had at least 89 percent sequence homology with enterovirus 71 MS isolates. The isolates in cluster 1 formed two subclusters. The isolate from Japan and five of the six isolates from Singapore were clustered with isolates from the Malaysian peninsula, forming one subcluster, and the remaining isolates, which included others from the Malaysian peninsula, Sarawak, and Singapore, formed the other subcluster.

Three other isolates examined, one from Singapore and two from Taiwan, were in cluster 2, which consisted mostly of isolates from the 1998 outbreak in Taiwan. Cluster 2 also had two subclusters, with all the isolates from Taiwan, including the two sequenced in this study, in one subcluster and the remaining isolates from the Malaysian peninsula and Singapore in the other. The isolates in these two subclusters had at least 97 percent homology with each other and approximately 85 percent homology with the coxsackievirus A9 5' UTR sequence rather than with the enterovirus 71 MS group, which contained the other enterovirus 71 strains found predominantly in Malaysia and Singapore. A comparison of the 5' UTR secondary RNA structure, which has been associated with the degree of virulence, in the cluster 2 isolates revealed no significant differences in the structure of the three domains within the 5' UTR sequence.

These findings suggest that the 5' UTR features of the enterovirus 71 strains from the Taiwanese outbreak were almost identical to those of the coxsackievirus A9–like strains isolated previously in the Malaysian peninsula.3 Because of these similarities and the high frequency of travel between Malaysia and Taiwan, it is tempting to speculate that the predominant enterovirus 71 strains in the Taiwanese outbreak may have been accidental imports.

Sazaly AbuBakar, Ph.D.
Yoke-Fun Chan, B.Sc.
Sai Kit Lam, Ph.D.
University of Malaya, 50603 Kuala Lumpur, Malaysia

3 References

1. 1

   Ho M, Chen E-R, Hsu K-H, et al. An epidemic of enterovirus 71 infection in Taiwan. N Engl J Med 1999;341:929-935
   Full Text | Web of Science | Medline

2. 2

   AbuBakar S, Chee H-Y, Al-Kobaisi MF, Xiaoshan J, Chua KB, Lam SK. Identification of enterovirus 71 isolates from an outbreak of hand, foot and mouth disease (HFMD) with fatal cases of encephalomyelitis in Malaysia. Virus Res 1999;61:1-9
   CrossRef | Web of Science | Medline

3. 3

   AbuBakar S, Chee H-Y, Shafee N, Chua KB, Lam SK. Molecular detection of enteroviruses from an outbreak of hand, foot and mouth disease outbreak in Malaysia in 1997. Scand J Infect Dis 1999;31:331-335
   CrossRef | Web of Science | Medline

Author/Editor Response

The authors reply:

To the Editor: In response to AbuBakar et al., we refer first to a phylogenetic study of enterovirus 71 isolates from 1997 and 1998, reported by Shimizu et al.,1 in which one of us participated as a coinvestigator. Eleven isolates from Japan, 5 from Malaysia, and 13 from Taiwan were analyzed. The isolates were classified as genotype group A (subgroup A₁ or A₂) or genotype group B. Six strains from Japan, 1 strain from Malaysia, and 10 strains from Taiwan were in group B, and 5, 4, and 3 strains, respectively, were in group A (subgroup A₂). Although the isolates were not homogeneous, the majority of the Malaysian isolates were in group A, whereas the Taiwanese isolates were in group B.

Shimizu et al. arrived at this classification by analyzing the VP4 and VP2 regions.1 By analyzing, as did AbuBakar et al., the 5' noncoding region, two of us also found that the majority of the Taiwanese and Malaysian strains were clustered in different groups. In a study of 60 enterovirus 71 isolates from patients in various parts of Taiwan, one of us found that only 5 isolates were in group A, whereas 55 were clustered in group B.

To date, enterovirus 71 group B consists mainly of Japanese and Taiwanese isolates of recent origin. It is unclear whether the Malaysian isolates studied by AbuBakar and colleagues have been available to other investigators. If they have not been available, many of the Malaysian isolates, contrary to our findings and those of Shimizu et al.,1 may belong to group B. If this is the case, the findings of AbuBakar et al. need to be confirmed, and more strains should be studied. Even so, it would not be possible to conclude that the Taiwanese strains came from Malaysia. They could just as well have come from Japan. It is premature to reach definite conclusions about the precise geographic movements of the Japanese, Malaysian, and Taiwanese strains.

We and our coauthors, many of whom are in the Taiwan Department of Health, would like to acknowledge with gratitude the assistance of the Centers for Disease Control and Prevention in the investigation of the enterovirus 71 epidemic in Taiwan. Specifically, we would like to thank Drs. Anthony W. Mounts, Umesh P. Parashar, and Wun-Ju Shieh of the investigative team, who were in Taiwan in June 1998.

Monto Ho, M.D.
National Health Research Institutes, Taipei 115, Taiwan

Jen-Ren Wang, Ph.D.
National Cheng Kung University Medical Center Virus Laboratory, Tainan 704, Taiwan

Shin-Ru Shih, Ph.D.
Chang Gung Medical Center Virus Laboratory, Lin Ko 333, Taiwan

1 References

1. 1

   Shimizu H, Utama A, Yoshii K, et al. Enterovirus type 71 from fatal and nonfatal cases of hand, foot and mouth disease epidemics in Malaysia, Japan and Taiwan in 1997-1998. Jpn J Infect Dis 1999;52:12-15
   Web of Science | Medline

Citing Articles (5)

Citing Articles

1. 1

   (2008) The vignette for V15 N3 issue. Journal of Biomedical Science 15:3, 271-274
   CrossRef

2. 2

   Tzu-Chun Chen, Shu-Cheng Liu, Peng-Nien Huang, Hwan-You Chang, Jyh-Haur Chern, Shin-Ru Shih. (2008) Antiviral activity of pyridyl imidazolidinones against enterovirus 71 variants. Journal of Biomedical Science 15:3, 291-300
   CrossRef

3. 3

   Miren Iturriza-Gómara, Brian Megson, Jim Gray. (2006) Molecular detection and characterization of human enteroviruses directly from clinical samples using RT-PCR and DNA sequencing. Journal of Medical Virology 78:2, 243-253
   CrossRef

4. 4

   Jon Welch, Kate Maclaran, Tony Jordan, Peter Simmonds. (2003) Frequency, viral loads, and serotype identification of enterovirus infections in Scottish blood donors. Transfusion 43:8, 1060-1066
   CrossRef

5. 5

   Stephen B. Dunnett, Anders Björklund, Olle Lindvall. (2001) Cell therapy in Parkinson's disease – stop or go?. Nature Reviews Neuroscience 2:5, 365-369
   CrossRef