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Non-polio enteroviruses are common and distributed worldwide. Although infection often has no symptoms and goes 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.

Clinical syndromes

Replication of the enterovirus begins in the gastrointestinal or respiratory tract and once the virus is present in the blood stream, infection may affect various tissues and organs, causing a variety of diseases. The majority of infections are symptomless or mild in nature, the most common effect being a non-specific illness, with fever. Other manifestations include exanthems (rashes), herpangina (vesicular eruption and inflammation of the throat), acute respiratory disease, conjunctivitis, aseptic meningitis, encephalitis (inflammation of the brain), myopericarditis (inflammation of the heart tissue), and, occasionally, paralytic diseases. Many enteroviruses are associated with specific syndromes: for example, the viruses within the Human enterovirus B species more commonly cause meningitis or myopericarditis and those within the Human enterovirus A species more commonly cause hand-foot-mouth disease (rash especially on the palms and soles with vesicular eruption and inflammation of the mouth).

Diagnosis

Clinically, it is difficult to distinguish the specific cause of most enteroviral infections. Diagnostic testing for non-polio enteroviruses requires specialized laboratory facilities. Diagnosis is made by detecting virus in throat or faecal samples or, more convincingly, from specimens collected from the affected part of the body, for example, cerebrospinal fluid (CSF), biopsy material, and skin lesions. 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.

Epidemiology

Enteroviruses infecting humans are found worldwide and humans are the only known natural hosts. Young children are most susceptible to infection. In less developed areas, children may become infected during early infancy while in more socio-economically advanced areas, first infection may not occur until adolescence. Males more often develop clinically-recognizable diseases than females. Transmission is usually by the faeco-oral or by the respiratory route when there is an associated respiratory illness. The virus may be excreted in the stool for many weeks. Enteroviruses have been detected in water, soil, vegetables and shellfish and may possibly be transmitted in the community by contact with contaminated food or water.

The epidemiological pattern varies by geographical region and climate, but the incidence of infection is higher in the summer and autumn months in temperate climates while remaining prevalent year-round in tropical climates. Outbreaks of hand-foot-mouth disease associated with enterovirus infection have previously been reported from Taiwan, China (1998), and from Malaysia (1997). Outbreaks of aseptic meningitis associated with enterovirus infection have previously been reported from the Gaza Strip (1997) and Cyprus (1996).

Treatment

No specific antiviral agent is available for therapy of enterovirus infection. Treatment focuses on management of complications (for example, meningitis, abnormal cardiac rhythms, and heart failure). Intravenous administration of immune globulin may have a use in preventing severe disease in immunocompromised individuals or those with life-threatening disease.

Prevention and control

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 diaper changes or going to the toilet; disinfection of contaminated surfaces with bleach (20 ml/litre of water); and washing soiled articles of clothing. The viruses are resistant to many disinfectants so it is important to use chlorinated (bleach) or iodized disinfectants. During recognised epidemics, it may be advised to close certain institutions such as schools or child care facilities in order to reduce transmission especially among young children. It is not necessary to restrict travel or trade.