This post is about Poliomyelitis.
Poliomyelitis, or polio for short, was first described by Jakob Heine in 1840 but was known as long ago as Ancient Egypt. The virus causing it was identified in 1908 by Karl Landsteiner. Most cases are asymptomatic, but in approximately 3% of cases the virus enters the central nervous system where it specifically targets motor neurons, which are the nerve cells that control our muscles. This can lead to flaccid paralysis in the arms and/or legs, difficulty swallowing (if the glossopharyngeal nerve is attacked) and difficulty breathing (if the phrenic nerve that controls the diaphragm is attacked).
Poliomyelitis was endemic for millenia, and caused little harm. Poor sanitation meant that people were constantly exposed to the virus and became immune. Paradoxically, better sanitation stopped this constant exposure and resulted in a loss of immunity. In 1880, major outbreaks started in Europe. By 1910, epidemics were occurring all over the world. Interestingly, the older a person is when he or she gets polio, the worse his or her prognosis becomes. One famous victim was Franklin D. Roosevelt, who developed polio at age 39.
Because polio attacks the nerves, there is no cure. It is possible with modern medicine to aid recovery and raise the odds of survival. The Iron Lung saved many lives and individuals with weakened limbs can be rehabilitated with physical therapy and supports, but sufferers of acute flaccid paralysis will have diminished quality of life.
Three different vaccines have been developed against Polio. The first, based on live attenuated virus, was invented by Hilary Koprowski. It protected against serotypes PV-1 and PV-3. The second, based on inactivated polio virus and unimaginatively named Inactivated Poliovirus Vaccine (IPV) was developed in 1952 by Jonas Salk. Three injections of IPV confer 99% immunity. The third was the Oral Polio Vaccine (OPV) created by Albert Sabin. Three doses of OPV confer 95% immunity.
OPV was initially the vaccine of choice for its low price and high effectiveness. On very rare occassions (1 in 750,000) the attenuated virus can revert to a paralytic form. Salk’s IPV is now the vaccine of choice in most countries.
Campaigns to reduce polio have been wildly successful. Currently, polio is endemic in only four countries: Nigeria; India; Pakistan; and Afghanistan. In 2005 a Fatwah was issued in Nigeria declaring the Polio Vaccine a conspiracy to sterilise Muslims. The inevitable result was an outbreak.
From a high of hundreds of thousands of cases annually in the 1950′s, polio now infects fewer than 2,000 people a year. It is hoped that in the not-too-distant future, polio will join Smallpox and Rinderpest in extinction.