Poliovirus causes a wide spectrum of illness in unvaccinated people, such as (a) asymptomatic illness, (b) abortive polio-myelitis, (c) nonparalytic poliomyelitis, (d) paralytic polio, and (e) postpoliomyelitis syndrome. Incubation period is usually 10 days but may vary from 4 days to 4 weeks.
Most patients (90–95%) infected with poliovirus develop inap-parent infection and are asymptomatic. This asymptomatic illness is caused as a result of viral infection confined to the oropharynx and the intestine.
Abortive poliomyelitis is the minor illness occurring in approximately 5% of infected people. This is a febrile illness characterized by fever, headache, sore throat, loss of appetite, vomiting, and abdominal pain. Neurological symptoms are typically absent. The duration of this illness is usually less than 5 days.
Nonparalytic poliomyelitis also known as aseptic meningitis is caused by invasion of virus into the CNS. The symptoms of nonparalytic poliomyelitis are similar to those of abortive poliomyelitis but are more intense. Stiffness of the posterior muscles of the neck, trunk, and limbs is present in addition to the symptoms of the minor illness. This condition occurs in 1–2% of infected patients.
This is the major illness, which occurs in 0.1–2% of individuals infected with poliovirus. This is the most severe manifestation of poliomyelitis and appears 3–4 days after the abortive polio-myelitis has subsided. This condition is caused due to invasion of virus from blood to the anterior horn cells of the spinal cord and the motor cortex of the brain. Depending on the various tissues or organs affected and the intensity of neuronal infec-tion, poliomyelitis may be of two types, as follows:
Paralytic poliomyelitis: Paralytic poliomyelitis or spinalparalysis is characterized by spinal paralysis involving one or more limbs. Asymmetrical flaccid paralysis with no sensory loss is the typical manifestation. This condition is caused mostly by poliovirus type 1. This condition is seen in some of the vaccinated individuals following vaccination. This occurs due to reversion of the attenuated vaccine virus types 2 and 3 to virulence types. In this condition, there may be paralysis of only one limb, such as one leg or there may be complete flaccid paralysis of both the legs and hands. The condition may prog-ress to death or may recover completely with residual paralysis.
Bulbar poliomyelitis: This is caused due to involvement ofthe cranial nerves, most commonly 9th, 10th, and 12th. This condition tends to be more severe with involvement of the mus-cles of the pharynx, vocal cords, and respiration. The condition may cause death in 75% of the patients.
This condition is sequelae of poliomyelitis, which may develop 20–40 years after infection with poliovirus. This condition is seen in 20–80% of patients who have recovered from poliomy-elitis. Recurrence of weakness or fatigue is observed in this con-dition, and it usually involves the muscles that were initially affected by the poliovirus.