A third enterovirus, echo 7, has been identified during the current outbreak of HFMD in Malaysia. This virus was isolated from a fatal case in Universiti Hospital Kuala Lumpur (UHKL). The identification of this virus was conducted by Assoc. Prof. Dr. Chua Kaw Bing, consultant virologist of UHKL, along with clinical virologist Dr. Peter McMinn at the Princess Margaret Hospital, Perth.

Using VP4 RT-PCR and sequencing, the data generated were sent to Dr. Hiroaki Ishiko in Japan as he has an extensive database of VP4 sequence from all 66 human enteroviruses. This analysis provided an unequivocal match to echo 7. Further confirmation of echo 7 was made by VP1 RT-PCR and sequencing with a close match to a recent Spanish isolate (94% nucleotide sequence identity) and to the prototype Wallace strain (89% nucleotide sequence identity).

Neutralization assays were conducted using RD cells and a complete set of intersecting antiserum pools. This test confirmed the presumptive identification of echo 7 made by the VP4 and VP1 sequencing.

A serum neutralization assay on a convalescent serum from a 7-month old child showed a high neutralizing titre (1:320) to isolate 15394 (echo 7) and no cross-reactivity to the closely related echo 11 (<1:20). The convalescent serum from a 5-year old child showed the phenomenon of "original antigenic sin", with a neutralizing titre of 1:20 to echo 11 and <1:20 to the echo 7 virus isolate even though the virus was isolated from this child.

Echo 7 virus has been associated with several outbreaks involving central nervous system. One such outbreak in Pondicherry, India, was published in 1969 where there were 26 cases of encephalitis with several deaths. In Sweden in 1973, an outbreak of meningoencephalitis due to echo 7 and Coxsackie B3 was reported and echo 7 was isolated from 19 patients. There was no fatality during this outbreak.

During the present hand, foot and mouth outbreak, several enteroviruses have been isolated by UHKL. These included seven Coxsackie A16, fourteen enterovirus 71, one Coxsackie B, twelve herpes simplex and six echo 7. However, five of the six echo 7 virus isolates were from severe and fatal encephalitis.

The identification of echo 7 in severe and fatal cases during an outbreak of HFMD in Malaysia is of global interest because of the increase in emerging and re-emerging diseases worldwide.

Article sent to Promed on 25 October 2000


Ken Lam
Consultant Virologist
University Hospital Kuala Lumpur
19 October 2000

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