World Polio Day
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Poliomyelitis, often called polio or infantile paralysis, is an acute viral infectious disease spread from person to person, primarily via the fecal-oral route. The term derives from the Greek poliós (πολιός), meaning “grey”, myelós (µυελός), referring to the “spinal cord“, and the suffix -itis, which denotes inflammation.
Although around 90% of polio infections cause no symptoms at all, affected individuals can exhibit a range of symptoms if the virus enters the blood stream. In about 1% of cases the virus enters the central nervous system, preferentially infecting and destroying motor neurons, leading to muscle weakness and acute flaccid paralysis. Different types of paralysis may occur, depending on the nerves involved. Spinal polio is the most common form, characterized by asymmetric paralysis that most often involves the legs. Bulbar polio leads to weakness of muscles innervated by cranial nerves. Bulbospinal polio is a combination of bulbar and spinal paralysis.
Poliomyelitis was first recognized as a distinct condition by Jakob Heine in 1840. Its causative agent, poliovirus, was identified in 1908 by Karl Landsteiner. Although major polio epidemics were unknown before the late 19th century, polio was one of the most dreaded childhood diseases of the 20th century. Polio epidemics have crippled thousands of people, mostly young children; the disease has caused paralysis and death for much of human history. Polio had existed for thousands of years quietly as an endemic pathogen until the 1880s, when major epidemics began to occur in Europe; soon after, widespread epidemics appeared in the United States.
By 1910, much of the world experienced a dramatic increase in polio cases and frequent epidemics became regular events, primarily in cities during the summer months. These epidemics—which left thousands of children and adults paralyzed—provided the impetus for a “Great Race” towards the development of a vaccine. Developed in the 1950s, polio vaccines are credited with reducing the global number of polio cases per year from many hundreds of thousands to around a thousand. Enhanced vaccination efforts led by the World Health Organization, UNICEF, and Rotary International could result in global eradication of the disease.
- Polio (poliomyelitis) mainly affects children under five years of age.
- One in 200 infections leads to irreversible paralysis (usually in the legs). Among those paralysed, 5% to 10% die when their breathing muscles become immobilized.
- Polio cases have decreased by over 99% since 1988, from an estimated 350 000 cases then, to 1997 reported cases in 2006. The reduction is the result of the global effort to eradicate the disease.
- In 2008, only four countries in the world remain polio-endemic, down from more than 125 in 1988. The remaining countries are Afghanistan, India, Nigeria and Pakistan.
- Persistent pockets of polio transmission in northern India, northern Nigeria and the border between Afghanistan and Pakistan are the current focus of the polio eradication initiative.
- As long as a single child remains infected, children in all countries are at risk of contracting polio. Between 2003 and 2005, 25 previously polio-free countries were re-infected due to imports of the virus.
- In most countries, the global effort has expanded capacities to tackle other infectious diseases by building effective surveillance and immunization systems. Knowledge of the poliovirus has expanded with aggressive research carried out under the eradication effort.
- Success for the effort hinges on closing a substantial funding gap to finance next steps of the global eradication initiative.
- At the height of the polio epidemic in 1952, nearly 60,000 cases with more than 3,000 deaths were reported in the United States alone. However, with widespread vaccination, wild-type polio, or polio occurring through natural infection, was eliminated from the United States by 1979 and the Western hemisphere by 1991.
Polio is a viral illness that, in about 95% of cases, actually produces no symptoms at all (called asymptomatic polio). In the 4% to 8% of cases in which there are symptoms (called symptomatic polio), the illness appears in three forms:
- a mild form called abortive polio (most people with this form of polio may not even suspect they have it because their sickness is limited to mild flu-like symptoms such as mild upper respiratory infection, diarrhea, fever, sore throat, and a general feeling of being ill)
- a more serious form associated with aseptic meningitis called nonparalytic polio (1% to 5% show neurological symptoms such as sensitivity to light and neck stiffness)
- a severe, debilitating form called paralytic polio (this occurs in 0.1% to 2% of cases)
Two polio vaccines are used throughout the world to combat poliomyelitis (or polio). The first was developed by Jonas Salk and first tested in 1952. Announced to the world by Salk on April 12, 1955, it consists of an injected dose of inactivated (dead) poliovirus. An oral vaccine was developed by Albert Sabin using attenuated poliovirus. Human trials of Sabin’s vaccine began in 1957 and it was licensed in 1962. Because there is no long term carrier state for poliovirus in immunocompetent individuals, polioviruses have no non-primate reservoir in nature, and survival of the virus in the environment for an extended period of time appears to be remote. Therefore, interruption of person to person transmission of the virus by vaccination is the critical step in global polio eradication. The two vaccines have eradicated polio from most countries in the world, and reduced the worldwide incidence from an estimated 350,000 cases in 1988 to 1,652 cases in 2007. [wikipedia]
Polio cases have decreased by over 99% since 1988, from an estimated 350 000 cases in more than 125 endemic countries then, to 1997 reported cases in 2006. In 2008, only parts of four countries in the world remain endemic for the disease – the smallest geographic area in history.
The head of the World Health Organization’s polio eradication team has warned that India could reinfect the rest of the world with polio if a new outbreak of the disease is not rapidly brought under control. Officials are concerned by an “alarming” rise in the number of polio cases in the impoverished northern state of Uttar Pradesh, which has always been a troublesome epicenter of the disease. Because of the unexpected surge in cases there – with 121 cases recorded by the end of July, up from 12 in the same period last year – India is now the only country in the world where the incidence of polio is growing.
Polio remains significant among worldwide infectious disease threats
IDSA 48th Annual Meeting at VANCOUVER — A recent outbreak in Tajikistan has highlighted the fact that challenges remain for the polio eradication effort, in addition to other initiatives, according to findings presented at the 48th Annual Meeting of the Infectious Diseases Society of America. “Of course polio is present in south Asia and central and west Africa, but the big news in polio is the outbreak from Tajikistan to other countries from the former Soviet Union,” he said in a presentation. Dowell noted that both the number of cases and number of countries in which polio can be found are decreasing, but that the battle is far from over. [more reading]
Mutated virus confirms polio vaccine fears
A polio virus eradicated from India a decade ago has surfaced in a new avatar for a second consecutive year, paralysing three children and confirming long-standing fears about rare risks associated with the oral polio vaccine.
India has recorded a sharp drop in wild polio cases this year — 39 so far in contrast to 741 in 2009 — but one child in Tamil Nadu, and two children in Uttar Pradesh have been paralysed by vaccine-derived polio virus (VDPV) this year.
The VDPVs are mutated versions of the weakened, but live polio viruses used in the oral polio vaccine that have regained the ability to cause paralysis in humans. Such VDPVs first surfaced in India in 2009 — 17 cases in Uttar Pradesh, 3 in Bihar, and 1 in Assam.
Over the past decade, VDPVs have turned up in China, Egypt, Hispaniola, Finland, Indonesia, Myanmar and Pakistan. – “As long as oral polio vaccine continues to be used anywhere in the world, there will be a continued threat of VDPV and hence of outbreaks of (polio),” Philip Minor, a virologist at the National Institute for Biological Standards and Control in the UK, wrote last year in the journal Vaccine. [more reading]
Join hands to eradicate Polio Globally