What Is Polio?

Poliomyelitis is a highly infectious disease caused by the polio virus. It invades the nervous system, and can cause paralysis or even death in a matter of hours.

How is polio transmitted?

The polio virus (scientifically known as the wild polio virus or WPV) enters the body through water or food that has been contaminated with faecal material from an infected person. The virus multiplies in the intestine. From blood it may pass to the nerves of the brain stem and spinal cord. The disease mainly affects children under five years. Only humans can catch polio. The incubation period is three-five days for minor illness and one-two weeks for paralytic symptoms. So a large number of people may have had a minor dose of polio without really being aware of it. The original flu like illness, the more chance there is of deterioration occurring later in life (fatigue & weakness).

What are the different strains of polio?

Paralytic polio can be caused by any of three closely related strains (serotypes) of poliovirus - PV1 (poliovirus 1), PV2 and PV3. PV1 is the most virulent and produces the most severe paralysis. According to the Union Ministry of Health and Family Welfare, one out of every 200 children in India is infected with this virus.

People with PV2 are often first diagnosed as having meningitis and may have gone into a coma, but often the paralysis is less severe. Those who have PV2 are more likely to have had encephalitis polio and possible coma. Damage to the brain can lead to poor memory, problems in keeping awake or falling and staying asleep. PV2 is a weaker virus and has been eradicated from India.

PV3 is more likely to be found where there are reports of sporadic cases, not in epidemics. The rate of infection in PV3 is one in 1,000. This strain had been confined to western Uttar Pradesh for the past two years but has now spread to other districts of the state and also Bihar. Those who have PV3 seem to be more prone to developing Chronic Fatigue or Parkinson's later in life.

There are twelve other viruses that are closely related to polio and can cause paralysis. If they had been discovered before polio vaccines stopped polio they would probably have been recorded as other polio types. At present there is no vaccine for the other types as everything is geared at eliminating the three known polio strains. But people are still being paralysed by these other strains, now called acute flaccid paralysis.