Polio Virus

Source:  Polio Virus    Tag:  poliovirus types

Polio Virus:

Introduction:

Polio is known in full as poliomyelitis – also called infantile paralysis. It is an acute viral infectious disease of the nervous system that usually begins with general symptoms such as fever, headache, nausea, fatigue, and muscle pains and spasms and is sometimes followed by a more serious and permanent paralysis of muscles in one or more limbs, the throat, or the chest. More than half of all cases of polio occur in children under the age of five. The paralysis so commonly associated with the disease actually affects fewer than 1 percent of persons infected by the poliovirus.



Between 5 and 10 percent of infected persons display only the general symptoms outlined above, and more than 90 percent show no signs of illness at all. For those infected by the poliovirus, there is no cure, and in the mid-20th century hundreds of thousands of children were struck by the disease every year. Since the 1960s, thanks to widespread use of polio vaccines, polio has been eliminated from most of the world, and it is now endemic only in several countries of Africa and South Asia. Approximately 1,000–2,000 children are still paralyzed by polio each year, most of them in India.


History:

A notable year in the history of polio was 1789, during which Michael Underwood first described a debility of the lower extremities in children that was recognizable as polio. Polio outbreaks were first reported in the United States in 1843. A turning point for the disease occurred in 1955, following the introduction of an inactivated polio vaccine (IPV). The decline in the incidence of polio continued following oral polio vaccine (OPV) introduction in 1961.
Signs and Symptoms:
When a person becomes infected with poliovirus, the virus begins to multiply within the cells that line the back of the throat, nose, and intestines. Polio symptoms usually appear 7 to 14 days after a person becomes infected with the poliovirus. This period between polio transmission and the start of symptoms is called the "polio incubation period." The incubation period for polio can be as short as 4 days or as long as 35 days.
Up to 95 percent of people who are infected with poliovirus will have no symptoms. However, people who are infected and do not have polio symptoms can still spread the poliovirus and cause others to develop polio.

If a person does develop symptoms, the symptoms can be categorized into one of three groups, which include:

        Minor polio symptoms (also known as abortive poliomyelitis)
        Aseptic meningitis
        Paralytic poliomyelitis. 

Causes:

Poliovirus is a very contagious virus that can spread easily from person to person. In fact, when a person is infected with poliovirus, it is expected that polio transmission among susceptible household contacts will occur in nearly 100 percent of children and over 90 percent of adults.

Poliovirus is a single-stranded RNA virus from the family Picornaviridae and genus enterovirus.

Poliovirus only infects humans. It is more common during summer months in temperate climates. In tropical climates, there is no seasonal pattern. The poliovirus is rapidly inactivated by heat, formaldehyde, chlorine, and ultraviolet light.

Prevention:
Polio prevention begins with polio vaccination. Polio vaccine is highly effective in producing immunity to the poliovirus and protection from paralytic polio. Approximately 90 percent or more of polio vaccine recipients develop protective antibodies to all three poliovirus types after two doses, and at least 99 percent are immune following three doses. If vaccinations were stopped, polio would return to pre-vaccine levels in the United States and hundreds of people would die from polio-related illnesses.
Polio vaccine in the United States is administered as an inactivated polio vaccine that contains no live poliovirus. Polio vaccine is highly effective in producing immunity to the poliovirus and protection from paralytic polio. Approximately 90 percent or more of polio vaccine recipients develop protective antibodies to all three poliovirus types after two doses, and at least 99 percent are immune following three doses.

There is no cure for polio, only treatment to alleviate the symptoms.  Heat and physical therapy is used to stimulate the muscles and antispasmodic drugs are given to relax the muscles. While this can improve mobility, it cannot reverse permanent polio paralysis.