This is one of the smallest known viruses. It has a diameter of about 17-30nm. It has single stranded RNA with an icosahedral capsid. It multiplies rapidly in nerve cells, producing over 10,000 new particle during a single cycle of about six hours. This virus enters the body through contaminated food or water in the gastrointestinal tract, there may be end at this point. However, in some cases, it is then localized on the gray matter of the spinal cord. The world polio is taken from the Greek word "polios" meaning gray. Meningitis may occur and paralysis experienced in the muscles of arms, legs, trunk and other area's controlled by spinal cord. This condition is after called asceptic meningitis.
The more serious form of polio is the one in which the virus infects stem of the brain, known as medulla. This condition is called bulbar polio, due to bulb like appearance of medulla. The nerves of the upper body portion are affected. Swallowing becomes difficult and paralysis occurs in the tongue, facial muscles and neck. Three types of polio virus are known to exist. Type 1, the Brenhindle strain, causing moderate cases of paralysis. Type 2, the Lansing strain, is occurring sporadically but including greatest percentage of paralytic cases. Type 3, the Leon strain, also occurring sporadically but virus confined to intestine, really causing paralysis. Albest sabin and his groups developed a vaccine. This vaccine may be taken orally and is in current use in these days. It produces more antibodies providing all three types of polio viruses, said to be trivalent.
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