Enterovirus 71
Posted by ajcann on May 12, 2008
Over the past week, international news stories have concentrated on the devastating cyclone in Burma (Myanmar), and the almost certain consequence of disease outbreaks in the aftermath. But at the same time, there’s another microbiology story unfolding in East Asia. Beginning in March, a large outbreak of hand, foot and mouth disease (HFMD) was reported from Fuyang city in Anhui Province in China. Note that HFMD is a human disease caused by enteroviruses belonging to the picornavirus family, but is not the same as the animal disease foot and mouth (FMD) caused by a different kind of picornavirus.
HFMD usually affects infants and children, is quite common worldwide and can be caused by a number of different enteroviruses. It is highly contagious and is spread through direct contact with the mucus, saliva, or faeces of an infected person. Like other enterovirus infections (including polio), HFMD typically occurs in small epidemics, usually during the summer and autumn months with an incubation period of 3-7 days.
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Enterovirus infections are common and occur worldwide. Although many infections show no symptoms and often go unnoticed, these viruses are also associated with occasional outbreaks in which a larger than usual number of patients develop clinical disease, sometimes with fatal consequences. The current outbreak is one of these. Initial testing for a variety of respiratory diseases did not reveal any conclusive results, but on April 23, the presence of Enterovirus (EV71) was confirmed. As of May 8th, at least 30 deaths had been reported and the disease had spread to 11 cities and several provinces across China. In all the fatal cases, which represent less than 1% of the thousands of children infected, the victims died with serious complications such as neurogenic pulmonary oedema (breathing difficulties reminiscent to those seen in polio victims).
Enterovirus replication begins in the gastrointestinal or respiratory tract but once the virus is present in the bloodstream may affect various tissues and organs, causing a variety of diseases. Clinically, it is difficult to distinguish the specific cause of most enterovirus infections. Diagnostic testing for non-polio enteroviruses requires specialized laboratory facilities. Diagnosis is made by detecting virus in the throat, in faecal samples or, more convincingly, from specimens collected from the affected part of the body, for example, cerebrospinal fluid (CSF) or biopsy material. A four-fold rise in the level of neutralizing antibody in specimens collected during the acute and convalescent phases of illness provides the best evidence for a recent infection. No specific antiviral agents are currently available for treatment of enterovirus infections, although intravenous administration of immune globulin may have a use in preventing severe disease in immunocompromised individuals or those with life-threatening disease.
EV71 was first isolated in an outbreak of neurological disease in California in 1969. One of the nastier enteroviruses, EV71 has been associated with several epidemics of severe neurological disease in children, mostly in East Asia. An outbreak in Taiwan in 1998 resulted in 129,106 reported cases, 405 children hospitalized and more than 80 deaths. EV71 appears to be emerging as an important virulent neurotropic enterovirus just as poliomyelitis is nearing eradication, but little is known about the molecular mechanisms of host response to EV71 infection.
Transmission of enterovirus infections is increased by poor hygiene and overcrowded living conditions. Improved sanitation and general hygiene are important preventive measures. Measures that can be taken to avoid getting infected with enteroviruses include frequent handwashing, especially after nappy (diaper) changes or going to the toilet, disinfection of contaminated surfaces with bleach, and washing soiled articles of clothing. Enteroviruses are quite resistant to many disinfectants so it is important to use chlorinated (bleach) or iodized disinfectants. During recognised epidemics, it may be advised to close institutions such as schools or child care facilities in order to reduce transmission among young children. Chinese public health experts currently predict that the number of cases will continue to increase and peak around June-July.
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