Kolkata, Sep 1: Poliomyelitis is an acute communicable disease of humans caused by a human enterovirus of the Picornaviridae family.
The virus is composed of a single-stranded, positive-sense RNA genome and a protein capsid. The 3 serotypes of poliovirus carry are antigenically distinct. Poliovirus is transmitted from one person to another by oral contact with secretions or faecal material from an infected person. Most poliovirus infections cause asymptomatic viral replication that is limited to the alimentary tract.
However, following an incubation period of approximately 7–10 days (range, 4–35 days), about 24 per cent of those infected develop clinical signs such as fever, headache and sore throat (considered a minor illness).
Paralytic poliomyelitis, experienced in less than 1% of poliovirus infections, occurs when the virus enters the central nervous system and replicates in anterior horn cells (motor neurons) of the spinal cord. When it multiplies in the nervous system, the virus can destroy nerve cells (motor neurons) which activate skeletal muscles. The affected muscles lose their function due to a lack of nervous enervation, a condition known as acute flaccid paralysis.
In the most severe cases (bulbar polio), poliovirus attacks the motor neurons of the brain stem, reducing breathing capacity and causing difficulty in swallowing and speaking. Without respiratory support, bulbar polio can result in death. Polio can strike at any age, but affects mainly children under three.
In May 1988 the World Health Assembly resolved to eradicate polio from the world. As a result of this eradication program, the number of poliomyelitis cases have been reduced by over 99 per cent, and the endemic circulation type 2 virus has been halted.
However, a small number of countries have not yet succeeded in stopping endemic transmission of polio, resulting in small sporadic outbreaks caused by travellers. When poliovirus transmission is successfully halted, a globally coordinated programme of containment of remaining wild poliovirus stocks and a discontinuation of the live oral polio vaccine will be required. (UNI)