What are the different strains of polio?

Paralytic polio can be caused by any of three closely related strains (serotypes) of poliovirus — PV1 (poliovirus1), 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 encephalitic 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; the last case was reported from Aligarh in 1999.

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 12 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.

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