Why undertake enterovirus surveillance?
- Why undertake enterovirus surveillance?
- What is hand-foot-and-mouth disease
- Neurological disease caused by EV71
- How is EV71 transmitted from person to person?
- What can be done to prevent EV71 infection?
The human enterovirus type 71 (EV71) was first identified in California in 1969 and is recognised as a major cause of hand-foot-and-mouth disease (HFMD) epidemics associated with severe neurological complications in young children. Since 1997 there has been a large increase in EV71 circulation and epidemic activity throughout the Asia-Pacific region. Recent HFMD epidemics in Malaysia, Singapore and Taiwan have been associated with a severe form of brainstem encephalitis associated with pulmonary oedema and high mortality rates. We do not understand why this rise in EV71 activity has occurred.
The emergence of EV71 as a cause of large-scale epidemics of encephalitis is reminiscent of the emergence of epidemic poliomyelitis in Europe and North America during the early Twentieth Century and it is possible that EV71 may become the major infectious cause of acute neurological disease in the world following the eradication of poliovirus. Therefore, it is imperative that medical and public health researchers prepare for such an eventuality in order to avoid the large-scale loss of life and human potential that resulted from the poliomyelitis epidemics of the Twentieth Century and that has already occurred as a result of the EV71 epidemics in our region.
Exciting developments in the techniques of molecular biology over the past twenty-five years have provided us with powerful tools to combat epidemics of EV71. It is critically important for us to use these tools to prevent EV71 infection through the development of regional surveillance to predict impending epidemics and to develop vaccines to protect our children from the devastating neurological consequences of this disease.
Figure 1 - Asia-Pacific countries affected by EV71 epidemics since 1997
Hand-foot-and-mouth disease (HFMD) is a mild blistering (vesicular) rash illness of young children that is caused by enteroviruses belonging to the human enterovirus A species, which includes EV71. The vesicles are typically small and occur on the palms of the hand, soles of the feet and around the mouth and lips (See Figure 2). Vesicles may also occasionally occur on the buttocks. The rash is frequently accompanied by fever and the illness typically lasts for 4-7 days and is followed by complete recovery.
Figure 2 - Typical hand and face lesions of hand-foot-and-mouth disease
Although several of the human enterovirus A species viruses cause HFMD, in particular Coxsackievirus type A16, EV71 is the major virus of this group to be associated with acute neurological disease. It is estimated that one in every few hundred cases of EV71 infection may be complicated by neurological disease. EV71 causes several neurological diseases, including mild aseptic meningitis (most commonly), poliomyelitis-like paralytic disease of the spinal cord (see Figure 3) and encephalitis of the brainstem. The latter is the most severe form of EV71 neurological disease, with high mortality rates (40-80%) and high rates of residual neurological morbidity.
Figure 3 - Destruction of the spinal cord due to poliomyelitis-like EV71 disease
Young children constitute the principal target and reservoir of enteroviruses, including EV71. The primary site of enterovirus replication is within the gastrointestinal tract. Virus is shed in the faeces for up to several weeks after infection. The primary mode of enterovirus transmission is via the faecal-oral route, with very efficient spread occurring within families and in childcare centres. Direct faecal contamination of hands, thence food or eating utensils, is probably responsible for most of the spread between people, especially under crowded conditions of poor hygiene and sanitation. The chain of virus transmission is rarely obvious because the majority of EV71 infections are inapparent or involve mild undifferentiated fevers or upper respiratory tract infections.
As EV71 is transmitted via the faecal-oral route, control rests with improved standards of public and personal hygiene. In particular, hand washing after going to the toilet or after changing an infant's nappy is very effective in preventing EV71 transmission. During EV71 epidemics in Taiwan and Singapore, public health interventions such as closing schools and childcare centres were also found to be effective in limiting virus transmission within the community.
Ultimately, effective control of EV71 infection will require development of a vaccine. Mass vaccination has been spectacularly effective in controlling the related polioviruses. Vaccine development is a major research priority of scientists working within APNET.