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The polioviruses

The polioviruses are a group of enteroviruses that cause poliomyelitis, also called polio or infantile paralysis. This is a highly infectious viral disease that may attack the central nervous system and is characterized by symptoms that range from a mild nonparalytic infection to total paralysis in a matter of hours. It is important to note, however, that most of poliovirus infections are asymptomatic, just as with all enteroviruses.

There are three types of polio diseases that can result from infection: abortive, non-paralysis, and paralysis.

Abortive polio has symptoms similar to those of other viral infections, including fever, headache, sore throat, loss of appetite, vomiting, and abdominal pain. Neurological symptoms are typically not reported.

Non-paralytic polio symptoms are similar to those of abortive polio but are more intense. Patients report stiffness of the posterior muscles of the neck, trunk, and limbs.

Paralytic polio symtoms are similar to nonparalytic polio, with weakness of one or more muscle groups. Exercise increases the severity of paralytic polio, especially during the first 3 days of major illness. Intramuscular injections or skeletal muscle injury predisposes to localization of polio to that extremity (termed provocation poliomyelitis).

  • Spinal: Patients have a prolonged prodrome, with features of aseptic meningitis followed in 1-2 days by weakness and, eventually, paralysis.
  • Bulbar: Cranial nerves are involved, most commonly IX, X, and XII. Tonsillectomy increases the risk of bulbar polio. Patients are unable to swallow smoothly. They accumulate pharyngeal secretions; have a nasal twang to the voice; and develop paralysis of vocal cords, causing hoarseness, aphonia, and, eventually, asphyxia.
  • Polioencephalitis: This form is principally reported in children. Unlike in other forms of polio, seizures are common and paralysis may be spastic.

There is no cure for polio; but it can be prevented. Polio vaccine, given multiple times, can protect a child for life.

The Global Polio Eradication Initiative

Overall, in the twenty years since the Global Polio Eradication Initiative began, the number of cases has fallen by over ninety-nine percent. In 2008, only four countries in the world remain polio-endemic.

In 1994, the World Health Organization (WHO) Region of the Americas (36 countries) was certified polio-free, followed by the WHO Western Pacific Region (37 countries and areas including China) in 2000 and the WHO European Region (51 countries) in June 2002.

In 2007, more than 400 million children were immunized in 27 countries during 164 supplementary immunization activities (SIAs). Globally, polio surveillance is at historical highs, as represented by the timely detection of cases of acute flaccid paralysis.

Persistent pockets of polio transmission in northern India, northern Nigeria, and in the border between Afghanistan and Pakistan are key epidemiological challenges.