Polio

Transmission is faecal-oral. Most infections are asymptomatic or cause a minor illness with fever and sore throat; about one per cent progress to aseptic meningitis, and a small fraction to paralytic disease. The virus replicates in the oropharynx and gut, spreads via the bloodstream, and reaches the anterior horn cells of the spinal cord and the motor nuclei of the brainstem. The resulting lower motor neuron syndrome gives asymmetric flaccid weakness, hypotonia, absent reflexes, fasciculations, and eventual atrophy, with entirely intact sensation because the dorsal columns and spinothalamic tracts are spared — the same pattern seen in spinal muscular atrophy (Werdnig-Hoffmann) and West Nile virus. Bulbar involvement threatens respiration. Diagnosis is by viral culture or PCR of stool or throat, and CSF shows a lymphocytic pleocytosis with normal glucose. There is no antiviral treatment; management is supportive with ventilation if needed. Post-polio syndrome is progressive weakness decades later. Prevention is vaccination, and eradication is nearly complete.