Polio overview

# Overview
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 polio (), meaning "grey", myelon (), referring to the "spinal cord", and -itis, which denotes inflammation. Although around 90% of polio infections have no symptoms at all, effected individuals can exhibit a range of symptoms if the virus enters the blood stream. In fewer than 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.

# Historical Perspective
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 20th century, polio was one of the most dreaded childhood diseases of the 20th century in the United States. 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 epidemicswhich left thousands of children and adults paralyzedprovided the impetus for a "Great Race" towards the development of a vaccine. The polio vaccines developed by Jonas Salk in 1952 and Albert Sabin in 1962 are credited with reducing the annual number of polio cases 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.

# Classification
The term poliomyelitis is used to identify the disease caused by any of the three serotypes of poliovirus. Two basic patterns of polio infection are described: a minor illness which does not involve the central nervous system (CNS), sometimes called abortive poliomyelitis, and a major illness involving the CNS, which may be paralytic or non-paralytic.

# Pathophysiology
The poliovirus is transmitted by the fecal-oral or oral route.  Acute infection involves the oropharynx, gastrointestinal tract, and occasionally the central nervous system.  Poliovirus divides within gastrointestinal cells for about one week before penetrating the intestinal lining. Once the virus enters the bloodstream it becomes a viremia and is widely-distributed throughout the body.  Rarely, the major viremia progresses and the virus invades the central nervous system, causing a local inflammatory response.

# Causes
Polio is a highly infectious disease caused by Poliovirus that invades the nervous system.  Poliovirus are small (2730 nm), nonenveloped viruses with capsids enclosing a single-stranded, positive-sense RNA genome about 7,500 nucleotides long.  Person-to-person spread of poliovirus via the fecal-oral route is the most important route of transmission, although the oral-oral route may account for some cases.

# Epidemiology and Demographics
Because of polio eradication efforts, the number of countries where travelers are at risk for polio has decreased dramatically. The last documented case of wild polio virus-associated paralysis in a US resident traveling abroad occurred in 1986 in a 29-year-old vaccinated adult who had been traveling in South and Southeast Asia. In 2005, an unvaccinated US adult traveling abroad acquired vaccine-associated paralytic poliomyelitis after contact with an infant recently vaccinated with oral polio vaccine.

# Risk Factors
Poliovirus is highly infectious, with seroconversion rates among susceptible household contacts of children nearly 100%, and greater than 90% among susceptible household contacts of adults. Persons infected with poliovirus are most infectious from 7 to 10 days before and after the onset of symptoms, but poliovirus may be present in the stool from 3 to 6 weeks.

# Natural History, Complications and Prpgnosis
Many cases of poliomyelitis result in only temporary paralysis.  After an interval of 3040 years, 25%40% of persons who contracted paralytic poliomyelitis in childhood experience new muscle pain and exacerbation of existing weakness, or develop new weakness or paralysis. This disease entity is referred to as pos-tpolio syndrome.  Patients with abortive polio infections recover completely. In those that develop only aseptic meningitis, the symptoms can be expected to persist for two to ten days, followed by complete recovery.

# Diagnosis

## History and Symptoms
Clinical manifestations of poliovirus infection range from asymptomatic (most infections) to symptomatic, including acute flaccid paralysis of a single limb to quadriplegia, respiratory failure, and rarely, death.

## Laboratory Findings
A laboratory diagnosis of poliomyelitis is usually made based on recovery of poliovirus from the stool or pharynx. Neutralizing antibodies to poliovirus can be diagnostic and are generally detected in the blood of infected patients early in the course of infection. Analysis of the patient's cerebrospinal fluid (CSF), which is collected by a lumbar puncture ("spinal tap") reveals an increased number of white blood cells (primarily lymphocytes) and a mildly elevated protein level. Detection of virus from the CSF is diagnostic of paralytic polio, but rarely occurs.

# Medical Therapy
Only treatment for symptoms is available, ranging from pain and fever relief to intubation and mechanical ventilation for patients with respiratory insufficiency.

# Prevention
Two polio vaccines are used throughout the world to combat polio. Both vaccines induce immunity to polio, efficiently blocking person-to-person transmission of wild poliovirus, thereby protecting both individual vaccine recipients and the wider community (so-called herd immunity).