The poliovirus (an enterovirus) is found worldwide and is transmitted from person to person by direct contact with infected oropharyngeal secretions or feces.

The virus usually enters the body through the alimentary tract, multiplies in the oropharynx and lower intestinal tract, and then spreads to regional lymph nodes and blood. Factors that increase the probability of paralysis include pregnancy, old age, unusual physical exertion at or just before the clinical onset of poliomyelitis, and localized trauma, such as a recent tonsillectomy, tooth extraction, or inoculation.

Possible complications include respiratory failure, pulmonary edema, pulmonary embolism, hypertension, urinary tract infection, urolithiasis, atelectasis, pneumonia, myocarditis, cor pulmonale, softtissue and skeletal deformities, and paralytic ileus.

In poliomyelitis survivors, latent poliomyelitis can lead to muscle spasticity and weakness 20 to 30 years after the initial infection. Delayed poliomyelitis also can affect respiratory muscles, leading to hypoxemia.

Today, most cases of poliomyelitis are so minor that the patient doesn’t even visit the physician. Inapparent, or subclinical, poliomyelitis (about 95% of all cases) has no symptoms. Abortive poliomyelitis (4% to 8% of all cases) is over in about 72 hours, with the patient experiencing only a slight fever, malaise, headache, sore throat, and vomiting.

The third type, major poliomyelitis, is most likely to be reported. It involves the central nervous system (CNS) and takes two forms: nonparalytic and paralytic. In children, the course commonly is biphasic, with the onset of major illness occurring after recovery from the minor illness stage.

The most perilous paralytic form, bulbar paralytic poliomyelitis, occurs when the virus affects the medulla of the brain. This type usually weakens the muscles supplied by the cranial nerves (particularly IX and X).

A patient with nonparalytic poliomyelitis complains of moderate fever, headache, vomiting, lethargy, irritability, and pains in the neck, back, arms, legs, and abdomen.

Paralytic poliomyelitis usually develops within 5 to 7 days after the onset of fever. The patient complains of symptoms similar to those of nonparalytic poliomyelitis and then develops weakness and paralysis. The patient may also report related signs and symptoms, such as paresthesia, urine retention, constipation, and abdominal distention.