Poliomyelitis Dr. Asif Rehman

Key Facts Polio (poliomyelitis) mainly affects children under 5 years of age. 1 in 200 infections leads to irreversible paralysis. Among those paralyzed, 5% to 10% die when their breathing muscles become immobilized. Polio cases have decreased by over 99% since 1988, from an estimated 350000 cases then, to 74 reported cases in 2015. The reduction is the result of the global effort to eradicate the disease. As long as a single child remains infected, children in all countries are at risk of contracting polio. Failure to eradicate polio from these last remaining strongholds could result in as many as 200 000 new cases every year, within 10 years, all over the world. In most countries, the global effort has expanded capacities to tackle other infectious diseases by building effective surveillance and immunization systems.

Key Facts Of the 3 strains of wild poliovirus (type 1, type 2, and type 3), wild poliovirus type 2 was eradicated in 1999 and case numbers of wild poliovirus type 3 are down to the lowest-ever levels with the no cases reported since a case reported by Nigeria in November 2012. Once polio is eradicated, the world can celebrate the delivery of a major global public good that will benefit all people equally, no matter where they live. Economic modelling has found that the eradication of polio would save at least US$ 40–50 billion between 1988 and 2035, mostly in low-income countries. Most importantly, success will mean that no child will ever again suffer the terrible effects of lifelong polio-paralysis.

Key Facts Polio is considered one of the most feared diseases. In the early 1950s, before polio vaccines were available, polio outbreaks caused more than 15,000 cases of paralysis each year in the United States. Following introduction of vaccines—specifically, trivalent inactivated poliovirus vaccine (IPV) in 1955 and trivalent oral poliovirus vaccine (OPV) in 1963—the number of polio cases fell rapidly. It takes only one traveler with polio to bring the disease into a country. The best way to keep a country polio-free is to maintain high immunity (protection) in the population against polio through vaccination

Poliomyelitis Polio= gray matter Myelitis= inflammation of the spinal cord This disease result in the destruction of motor neurons caused by the poliovirus. Poliovirus attacks the nerve cells of the brain & spinal cord although not all infections result in sever injuries and paralysis.

Causative Organism Poliovirus: belongs to “Picorna” viruses which are small RNA-containing viruses. Polioviruses have three antigenically distinct types, giving no cross immunity: Type I: “Leon”; the commonest in epidemics Type II: “Berlinhide”; the prevailing type in endemic areas. Type III: “Lansing”; occasionally causes epidemics. Polioviruses are relatively resistant and survive for a long time under suitable environmental conditions, but are readily destroyed by heat (e.g. pasteurization of milk, and chlorination of water.

Mode of Transmission Since foci of infection are the throat and small intestines, poliomyelitis spreads by two routes: Oral-oral infection: direct droplet infection Faeco-oral infection Polio virus has the ability to survive in cold environments. Overcrowding and poor sanitation provide opportunities for exposure to infection. People who don’t have symptoms can still pass the virus to others and make them sick.

Transmission

Symptoms Most people who get infected with poliovirus (about 72 out of 100) will not have any visible symptoms. About 1 out of 4 people with poliovirus infection will have flu-like symptoms that may include— Sore throat Fever Tiredness Nausea Headache Stomach pain These symptoms usually last 2 to 5 days then go away on their own.

Symptoms A smaller proportion of people with poliovirus infection will develop other more serious symptoms that affect the brain and spinal cord: Paresthesia (feeling of pins and needles in the legs) Meningitis (infection of the covering of the spinal cord and/or brain) occurs in about 1 out of 25 people with poliovirus infection Paralysis (can’t move parts of the body) or weakness in the arms, legs, or both, occurs in about 1 out of 200 people with poliovirus infection Paralysis is the most severe symptom associated with polio because it can lead to permanent disability and death. Between 2 and 10 out of 100 people who have paralysis from poliovirus infection die because the virus affects the muscles that help them breathe. Even children who seem to fully recover can develop new muscle pain, weakness, or paralysis as adults, 15 to 40 years later. This is called post-polio syndrome. Note that "poliomyelitis" (or "polio" for short) is defined as the paralytic disease. So only people with the paralytic infection are considered to have the disease.

Difference between IPV and OPV IPV is Inactivated (killed) virus vaccine while Oral Polio Vaccine is a live attenuated (harmless) vaccine IPV is more effective and has less risk of side effects as virus in vaccine is already killed. It is less heat sensitive. Weak point is that it does not provide local gut immunity as OPV. OPV is to be given by mouth. Less immunogenic and therefore more doses are required (at least 6). This needs efficient thermal protection. Since this vaccine is given by mouth and proliferates in intestine, it provides excellent local protection. Moreover, when excreted in stool, it makes herd immunity by feco-oral route. Both these vaccines have distinct advantages. IPV is safe and more effective but costly and in short supply.

Polio Eradication Polio is a crippling and potentially fatal infectious disease. There is no cure, but there are safe and effective vaccines. Therefore, the strategy to eradicate polio is based on preventing infection by immunizing every child to stop transmission and ultimately make the world polio free. In 1988, the World Health Assembly adopted a resolution for the worldwide eradication of polio. It marked the launch of the Global Polio Eradication Initiative (GPEI), spearheaded by national governments, CDC, Rotary International, WHO, and UNICEF, with substantial support from the Bill & Melinda Gates Foundation. Today, polio continues to circulate in three countries: Afghanistan, Pakistan, and Nigeria.

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