Polio

Infectious disease caused by the poliovirus

A child receiving a polio vaccine.

Polio, also known as poliomyelitis, is an infectious disease caused by the poliovirus. The virus spreads from person to person and can infect a person's spinal cord, leading to paralysis. While many infections result in no symptoms, some cases can lead to severe outcomes, including paralysis and even death.

Signs and symptoms

Electron micrograph of the poliovirus.

Most people infected with the poliovirus do not have any visible symptoms. However, about 25% of infected individuals may experience flu-like symptoms such as sore throat, fever, tiredness, nausea, headache, and stomach pain. These symptoms usually last 2 to 5 days and then go away on their own.

In a smaller proportion of cases, the virus can invade the nervous system and cause more severe symptoms, such as paresthesia (feeling of pins and needles in the legs), meningitis (infection of the covering of the spinal cord and/or brain), and paralysis or weakness in the arms, legs, or both. Paralysis is the most severe symptom associated with polio because it can lead to permanent disability and death.

Pathophysiology

Diagram of the human spine, which can be affected by poliovirus.

The poliovirus is a member of the genus Enterovirus, a group of small, RNA viruses. It primarily spreads through the fecal-oral route, meaning it is transmitted through contaminated water and food. Once ingested, the virus multiplies in the intestine and can invade the nervous system.

The virus specifically targets motor neurons in the spinal cord, brainstem, or motor cortex, leading to the characteristic muscle weakness and paralysis. The destruction of these neurons is what causes the paralysis associated with polio.

Diagnosis

Diagnosis of polio is based on clinical symptoms and laboratory tests. A sample of throat secretions, stool, or cerebrospinal fluid can be tested for the presence of poliovirus. Molecular techniques such as PCR (polymerase chain reaction) are commonly used to detect the virus.

Prevention

Oral polio vaccine being administered.

The most effective way to prevent polio is through vaccination. There are two types of vaccines available: the inactivated poliovirus vaccine (IPV) and the oral poliovirus vaccine (OPV). IPV is given as an injection, while OPV is administered orally.

Vaccination campaigns have significantly reduced the incidence of polio worldwide. The World Health Organization has been working towards the global eradication of polio, with significant progress made in reducing the number of cases.

Epidemiology

Graph showing the number of polio cases since 2000.

Polio was once one of the most feared diseases, causing paralysis and death across the world. However, due to widespread vaccination efforts, the number of polio cases has decreased dramatically. As of 2023, polio remains endemic in only a few countries.

Complications

A person with polio sequelae.

Complications of polio can include permanent muscle weakness, paralysis, and post-polio syndrome, a condition that affects polio survivors years after recovery. Post-polio syndrome is characterized by new muscle pain, weakness, or paralysis.

Treatment

There is no cure for polio once a person is infected. Treatment focuses on supportive care to alleviate symptoms. This may include pain relief, physical therapy, and the use of assistive devices such as braces or wheelchairs.

History

Orthotic device used for polio-affected leg.

Polio has been known since ancient times, with depictions of the disease found in ancient Egyptian art. The first clinical description of polio was made in 1789 by British physician Michael Underwood. Major polio epidemics began to occur in the late 19th century, and the disease reached pandemic proportions in the first half of the 20th century.

The development of effective vaccines in the 1950s and 1960s led to a dramatic decline in polio cases. The Global Polio Eradication Initiative, launched in 1988, has further reduced the incidence of polio worldwide.

Related pages

• Vaccine
• Infectious disease
• Virus
• Paralysis