Introduction
Polio is a commonly used termed for poliomyelitis. The term poliomyelitis was coined by German physician Adoplh Kussmaul in 1874. Poliomyelitis characterized by the inflammation of grey matter of the spinal cord occurs which is evident by its etymology derived from Greek words polios meaning grey, myelos meaning marrow, and itis stands for inflammation. Poliomyelitis is a disease of the nervous system and is caused by poliovirus, a positive sense RNA virus belonging to family picornaviridae.
History of Poliomyelitis
Poliomyelitis is an ancient disease and has been known to afflict mankind since the years of yore massively. Egyptians portraits from the 1365-1405 BC illustrated infants and children with deformed limbs taking the support of sticks to walk. It was 1879 when English physician Michael Underwood first defined poliomyelitis as “debility of lower extremities” (Mehndiratta, Mehndiratta, and Pande, 2014)
Vaccination
For the eradication and prophylaxis of polio, vaccination was performed all around the globe, and most regions of the world were declared polio-free except few developing countries where poliomyelitis is still endemic. Vaccines available for poliomyelitis are of two types, inactivated polio vaccine (IPV) or Salk vaccine developed by John Salk in 1955 and oral polio vaccine (OPV) that was developed by Albert Sabin that was made commercially available in 1961.OPV formulation contains the live attenuated virus. Both vaccines have their pros and cons. Salk vaccine(IPV) being safer as the virus is dead and can’t revert to pathogenic form causing vaccine-associated poliomyelitis(VAP) which have been reported in case of Sabin vaccine (OPV) but Sabin vaccine has been experimentally shown to be more efficient. Due to the high incidences of VAP, many countries have started using relatively expensive IPV. Four doses of vaccine are administered to children at the age of 2 months, four months, somewhere between 6-18 months and 4-6 years of age (Cdc.gov, 2018).
Vaccination has proved to be very successful, and a huge reduction in the number of cases of poliomyelitis speaks for the achievements of immunization.
Recent Outbreaks
Despite all the hard work being done to eradicate poliomyelitis, it is still endemic in some developing countries of the world, e.g., Pakistan, Afghanistan, India, Nigeria and few others and outbreaks occur frequently in countries that were once declared polio-free too. In 2013 in Syria a polio case was identified and soon after it, the number of cases raised to 10 and finally 35 (Akil and Ahmad, 2016). In 2014, 27 children were reported to be paralyzed by a virus 58 instances of Poliovirus type 2 was also reported in 2017.
Pathogenesis
The route of transmission of poliovirus is fecal-oral. After gaining entry into the body through the oral route, Virus establishes and multiplies in the alimentary mucosa and probably in Peyer’s patches and tonsils. This is followed by viremia as virus crosses the natural barriers to reach the bloodstream. Viremia facilitates the virus to invade CNS either by crossing the blood-brain barrier or through peripheral nerves, and it replicates in the neurons preferably in motor neurons (Nomoto, 2007). During the infection process, poliovirus deploys several strategies to evade the immune responses.
Signs and Symptoms
Most of the infected persons remain asymptomatic. Symptomatic persons fall into two major groups
1-Paralytic polio
2-Non-paralytic polio.
The symptoms of Nonparalytic or abortive poliomyelitis are fever, sore throat, headache, malaise, neck and back pain and stiffness of muscles and the symptoms usually subside within few weeks. Rarely, paralytic poliomyelitis can occur with alarmingly serious symptoms such as loss of reflexes, severe myalgias, difficulty in breathing and flaccid paralysis (Anthony N. van del, 2013). The disease may sometimes affect one side of the body relatively higher in intensity than the other.
References
Akil, L., & Ahmad, H. A. (2016). The recent outbreaks and reemergence of poliovirus in war and conflict-affected areas. International Journal of Infectious Diseases, 49, 40-46.
Cdc.gov. (2018). Vaccines: VPD-VAC/Polio/main page. [online] Available at: https://www.cdc.gov/vaccines/vpd/polio/index.html [Accessed 5 Apr. 2018].
Mehndiratta, M. M., Mehndiratta, P., & Pande, R. (2014). Poliomyelitis: historical facts, epidemiology, and current challenges in eradication. The Neurohospitalist, 4(4), 223-229.
Nomoto, A. (2007). Molecular aspects of poliovirus pathogenesis. Proceedings of the Japan Academy, Series B, 83(8), 266-275.
Noori, N., Drake, J. M., & Rohani, P. (2017). Comparative epidemiology of poliovirus transmission. Scientific reports, 7(1), 17362.
van den Pol, A. N. (2013). Polio, still lurking in the shadows. Journal of Neuroscience, 33(3), 855-862.
