– An acute, communicable viral infection that affects the central nervous system, producing a range of manifestations from a subclinical or mild nonfebrile illness to aseptic meningitis, muscle weakness, and paralysis.
Causes and Incidence
Polio is caused by three distinct polio enteroviruses belonging to the Picornaviridae family and labeled types 1, 2, and 3. Type 1 is the most paralytogenic and the most likely to cause an epidemic. Polio has been all but eradicated in most developed countries because of widespread vaccination. In developing countries, however, the once rare disease has reached an incidence as high as that in the United States before a vaccine was developed. The mortality rate ranges from 1% to 10%, depending on the severity and type of disease.
The polio virus enters the mouth after contact with infected feces or oral or respiratory secretions. It multiplies in the lymphoid tissue of the throat and ileum, producing a follicular necrosis. The incubation period ranges from 5 to 35 days, averaging 7 to 14 days. A transient viremia of 3 to 5 days’ duration occurs when the virus is transported via the bloodstream and autonomic nerve fiber endings to the central nervous system. The viremia disappears at the onset of disease symptoms. Paralysis results when extensive damage is inflicted on the motor neurons, resulting in atrophy of associated skeletal muscle fiber groups.
Most cases are subclinical and produce no signs or symptoms. Clinical disease may be either minor (abortive) or major. Major illness may or may not lead to paralysis. The person is infectious from the time of infection up to 6 weeks after infection.
Develops 3 to 5 days after exposure, accounts for 85% of clinical cases, occurs primarily in young children, no central nervous system involvement; slight fever, malaise, sore throat, headache, vomiting, anorexia, and abdominal pain lasting 24 to 72 hours
Develops 7 to 14 days after exposure, primarily in older children and adults; fever, severe headache, stiff neck and back, deep muscle pain, paresthesias, hyperesthesias; this may be followed by a loss of tendon reflexes and asymmetric weakness or paralysis, may involve lower extremity, respiratory, facial, palatal, pharyngeal, or bladder muscles
Complications, which arise primarily from major paralytic disease, include respiratory failure, hypertension, cor pulmonale, soft tissue and skeletal deformities, and paralytic ileus. In paralytic polio, 50% of affected individuals recover with no residual effects, 25% have mild disability, and 25% have severe permanent residual disability. Recovery of muscle function takes 6 months to 2 years. A postpoliomyelitis syndrome has been identified, which occurs several years after the initial attack of polio. The syndrome is characterized by profound fatigue, muscle weakness, fasciculations, and muscle atrophy.
The definitive diagnosis is made through culture of throat washings or fecal material or from convalescent serum antibody titers, which are four times higher than acute antibody titers.
Tracheostomy if needed in respiratory paralysis
Sabin (OPV) vaccine is recommended for all infants and children as prophylaxis; Salk (IPV) vaccine is recommended for individuals with underlying immunodeficiency disease; Salk vaccine is recommended for unvaccinated adults who are traveling to endemic or epidemic areas.
Mild disease: bed rest.
Major disease: strict bed rest in acute phase; hot, moist packs for muscle spasm and pain; intermittent catheterization for urinary retention; assisted ventilation for respiratory paralysis; suctioning for pooling secretions; physical therapy for weakened or paralyzed extremities; IVs, tube feedings for those unable to swallow; monitoring for aspiration of secretions; long-term rehabilitation for those with permanent residual disability.