Poliomyelitis

Poliomyelitis is an infection by the polio virus that affects the motor neurons of the central nervous system.

Learning Objective

Describe poliomyelitis and its effect on motor neurons

Key Points

Spinal polio is the most common type of polio and results in asymmetric paralysis, usually involving the legs.
Bulbar polio is infection of the cranial nerves and causes weakness and paralysis in muscles innervated by the cranial nerves, while bulbospinal polio occurs when both the cranial nerves and spinal nerves are affected.
Although approximately 90% of polio infections cause no symptoms at all, affected individuals can exhibit a range of symptoms if the virus enters the blood stream.

Terms

paralysis
The complete loss of voluntary control of part of person's body, such as one or more limbs.
poliomyelitis
acute infection by the poliovirus, especially of the motor neurons in the spinal cord and brainstem, leading to muscle weakness, paralysis and sometimes deformity
spinal polio
Spinal polio is characterized by asymmetric paralysis that most often involves the legs.
motor neuron
A neuron located in the central nervous system that projects its axon outside the CNS and directly or indirectly control muscles.

Example

Franklin D. Roosevelt is perhaps the most famous polio sufferer, though the late onset of the disease and symptoms brings the diagnosis into question. He contracted the virus at Campobello Island, where his family was vacationing, and suffered the characteristic muscular paralysis from the waist down. Although he was paralyzed by his illness, he never allowed the public to see him in a wheelchair and usually appeared standing, supported by his aides or children.

Full Text

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.

Although approximately 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.

Polio

Man on street with atrophy and paralysis of the right leg and foot due to polio.

BACKGROUND

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 19^th century, polio was one of the most dreaded childhood diseases of the 20^th 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 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.

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 today under a thousand. Enhanced vaccination efforts led by the World Health Organization, UNICEF, and Rotary International could result in global eradication of the disease.

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