Enteroviruses

Enteroviruses are spread through the respiratory route or through fecal contamination (hand-to-mouth).

Poliovirus causes poliomyelitis, chiefly a childhood disease, which, before the introduction of the Salk vaccine, had a high mortality rate. The virus spreads from the oropharynx to the gastrointestinal tract and from there to the lymphoid tissue. Here, it replicates and disseminates to the nervous tissue via the bloodstream. Within the nervous tissue, the virus selectively affects the motor neurons of the spinal cord and brainstem and, variably, the cortical motor neurons.

Clinically, a few days following a nonspecific infection, the patient develops meningeal signs and flaccid paresis or paralysis of the extremities, which may extend to the bulbar muscles. Survivors of the acute illness are left with a residual weakness that gradually resolves, either partially or fully. Several years after a paralytic poliomyelitis, a post polio syndrome may develop, characterized by progressive weakness and atrophy of the affected muscles.

The pathology of poliomyelitis is characterized by perivascular lymphocytic infiltrations in the leptomen-inges, spinal cord, and brainstem, and by neuronopha-gia and microglial nodules in the anterior horns of the spinal cord and brainstem gray matter (Fig. 6.8). The cortical motor, thalamic, hypothalamic, and cerebellar neurons are less affected. Residual neurons may show small intranuclear inclusions and, in chronic cases, the anterior horns are depleted of neurons and are gliotic (Fig. 6.9).

Coxsackie and echovirus infections in children and adults are major causes of aseptic meningitis and encephalitis. Cutaneous rashes, herpangina, carditis, and pleu-rodynia are systemic manifestations.

TABLE 6.3

RNA Viruses That Cause Acute Aseptic

Meningitis, Encephalitis, Myelitis

Enteroviruses

Arboviruses

Poliovirus

St. Louis encephalitis virus

Coxsackie virus

Eastern encephalitis virus

Echovirus

Western encephalitis virus

Paramyxoviruses

Venezuelan encephalitis virus

Mumps virus

California encephalitis virus

Measles virus

Japanese encephalitis virus

Parainfluenza virus

West Nile virus

Nipah virus

Rhabdovirus

Toga virus

Rabies virus

Rubella virus

Acute in the

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poliomyelitis. A. Motor neurons medulla are invaded by activated glia and mononuclear cells. Loose glial nodule at the site of *. * Ifll* ■ *YffT-^ffl^il disintegrated neurons (HE).

FIGURE 6.9

Chronic poliomyelitis. A. Lumbar spinal cord shows atrophy of one anterior horn (iron hematoxylin-picrofuchsin stain). B. Depletion of motor neurons (cresyl violet).

FIGURE 6.9

Chronic poliomyelitis. A. Lumbar spinal cord shows atrophy of one anterior horn (iron hematoxylin-picrofuchsin stain). B. Depletion of motor neurons (cresyl violet).

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