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Virology
Classification and Host Range
The enteroviruses comprise one class of the family Picornaviridae (table 1). They are distinguished from other picornaviruses by their acid stability. Enteroviruses are found in many mammalian and non-mammalian hosts. However, enteroviruses that infect humans represent a distinct group that are not found in other hosts.
Most human enteroviruses are subclassified into four subclasses.
Unlike rhinoviruses, enteroviruses maintain infectivity over a wide pH range (3-l0).
They are rapidly inactivated at temperatures >500C.
Pathogenesis of Enterovirus Infections
Transmission
Infection results from ingestion of fecally contaminated material or, less commonly, via contact with respiratory secretions.
The incubation period is characteristically 3-5 days between infection and onset of non-specific symptoms.
Infection and Viral Dissemination
Initial sites of replication include both the pharynx and terminal ilium
Virus is shed from the upper respiratory tract for 1-3 weeks, and from the feces for 38 weeks. The period of maximum communicability is during the first 2 weeks after infection.
Immunity to Infection
Immunity to enterovirus infection is serotype specific.
Passive humoral antibody confers protection from disease in low titer, and from both infection and disease in high titer.
Humoral antibodies also have an important role in the immune response to enterovirus infection. Patients with isolated B cell immunodeficiency are at risk of prolonged, severe infections.
Epidemiology
Epidemic and Endemic Behavior
Seasonal patterns
a. Although enterovirus infections occur throughout the year, they are strikingly more prevalent between June and October in temperate climates.
Population immunity
a. Adults usually have a seroprevalence of 30-80% against the more common, endemic enterovirus serotypes.
b. Periodic epidemics may result in accumulation of a sufficient cohort of susceptibles to sustain transmission of the epidemic serotype.
Age and Socioeconomic Status
1. Incidence rates of infection and disease are inversely proportional to age. Infants <12 months have the highest incidence of disease
2. Rates of infection and disease are also higher among children of lower socioeconomic classes.
C. Transmission
1. Both direct person-to-person transmission, and indirect transmission (via contaminated fomites, food, and water) probably occurs.
2. Transmission is most efficient in households and families. Secondary attack rates for infection of 30-90% within households.
V. Laboratory Diagnosis
A. Virus Isolation. Cell culture is labor intensive and expensive.
B. Polymerase Chain Reaction (PCR)
1. PCR has superior sensitivity compared to cell culture for identification of enteroviruses in CSF.
2. Experience with other specimens is more limited. PCR compares favorably to culture for throat and serum specimens, but may be