Poliomyelitis

Poliomyelitis, or polio, is an acute infectious disease of viral origin that can affect the central nervous system. It is a highly contagious condition, primarily contracted by children. Although it usually presents in a mild form, in severe cases, it can cause permanent paralysis and even death.

Currently, due to systematic vaccination, poliomyelitis outbreaks have almost disappeared.

Based on the degree of central nervous system involvement, polio is classified into two types:

• Minor illness or abortive poliomyelitis: A very mild form of the disease that does not affect the central nervous system.
• Major illness: Involves the central nervous system.
• Non-paralytic poliomyelitis: A severe form that does not cause paralysis.
• Paralytic poliomyelitis: A very severe and less common form that leads to paralysis.
• Spinal poliomyelitis: The infection affects the spinal cord.
• Bulbar poliomyelitis: The brainstem is compromised.
• Bulbospinal poliomyelitis: A combination of the previous two forms.

Since its first description in the 19th century, poliomyelitis was an endemic disease until the development of the first vaccine in 1954, followed by a second vaccine ten years later. Massive vaccination campaigns have led to the World Health Organization declaring the Americas (1994), the Western Pacific (2000), Europe (2002), Southeast Asia (2014), and Africa (2020) polio-free. However, some countries still experience active polio transmission, where the disease remains endemic.

Symptoms

In most cases, people infected with poliomyelitis do not develop symptoms. When symptoms do appear, they vary depending on the type of polio:

Abortive poliomyelitis:

Symptoms appear between three and five days after exposure to the virus and last up to three days. They resemble flu symptoms, including:

• Fever
• Headache
• Nausea and vomiting
• General discomfort: muscle, stomach, or throat pain

Non-paralytic poliomyelitis:

In addition to intensified flu-like symptoms, aseptic meningitis symptoms appear due to nervous system involvement:

• Severe headache
• Stiffness in the neck or back
• Neck pain
• Constipation and urinary problems

A second phase of symptoms may occur after an apparent improvement, featuring muscle weakness and decreased reflexes.

Paralytic poliomyelitis:

A severe progression of the non-paralytic form, lasting two to three days, with additional symptoms:

• Severe muscle pain
• Extreme skin sensitivity
• Tingling, numbness, or itching sensation in the skin
• Muscle spasms
• Asymmetric flaccid paralysis in the limbs, in spinal poliomyelitis cases—typically affecting one leg
• Difficulty swallowing, nasal regurgitation, and pharyngeal paralysis, in bulbar involvement cases

Causes

Poliomyelitis is caused by the poliovirus, a virus belonging to the enterovirus genus. Three serotypes of poliovirus have been identified, with type 1 being the most common. All three are highly virulent and produce the same symptoms.

The virus is transmitted through contact with the feces or saliva of an infected person or, less commonly, through the consumption of water or food contaminated with the virus. The poliovirus enters the body through the mouth, infecting the oropharynx and intestinal tract, replicating there, and reaching the cervical and mesenteric lymph nodes. It is then absorbed into the bloodstream and spreads throughout the body. This initial viremia is usually neutralized by the immune system, resulting in an asymptomatic infection. However, in rare cases, the virus continues replicating, leading to a second viremia that causes minor illness symptoms, and if it enters the central nervous system, it results in major illness.

Following the eradication of the virus through vaccination campaigns, most current poliomyelitis cases are not due to the wild-type virus but to vaccine-derived poliovirus from the oral polio vaccine. This vaccine contains attenuated viruses that, once ingested, replicate in the intestines and are excreted in feces, potentially spreading among individuals—particularly in areas with low immunization rates and poor hygiene conditions. This virus itself does not cause polio, but its transmission can lead to mutations that result in more virulent forms capable of causing the disease.

Risk Factors

Factors that increase the likelihood of contracting poliomyelitis include:

• Lack of vaccination
• Age: primarily affects children aged 4 to 15 years
• Compromised immune system
• Malnutrition
• Poor hygiene and sanitation conditions

The risk of developing neurological damage after contracting polio increases in the following cases:

• Pregnancy
• Recent tonsillectomy or intramuscular injection
• Impaired B lymphocyte function
• Physical exertion concurrent with the onset of central nervous system involvement

Complications

In bulbar poliomyelitis cases, paralysis can affect the respiratory and circulatory centers in the brainstem, compromising respiratory function. If the diaphragm or intercostal muscles become paralyzed, respiratory failure can occur, potentially leading to death.

Additionally, poliomyelitis can cause permanent complications such as chronic pain, muscle atrophy, paralysis, and bone or joint deformities due to muscle shortening, potentially resulting in lifelong disability.

Some patients who have had paralytic poliomyelitis develop post-polio syndrome years or decades after the initial infection. This syndrome is characterized by weakness, muscle pain and wasting, fatigue, and decreased endurance. Muscle contractions and atrophy may also occur.

Prevention

The most effective way to prevent polio is through vaccination. There are two types of polio vaccines:

• Salk vaccine (inactivated poliovirus vaccine - IPV): Contains a mixture of the three inactivated poliovirus types. It is administered via intramuscular injection. This vaccine prevents the disease but does not stop virus transmission.
• Sabin vaccine (oral poliovirus vaccine - OPV): Available in three different varieties, one for each type of polio. It contains live attenuated viruses and is administered orally. It provides immunity against the disease and prevents virus carriage. However, some countries have discontinued its use due to its association with vaccine-derived poliomyelitis.

For children, the vaccine is typically administered four times—at 2, 4, and 11 months and at 6 years—usually combined with other vaccines. Unvaccinated adults or those with incomplete vaccination should get vaccinated if they risk exposure to wild poliovirus, such as when traveling to endemic areas or working in laboratories handling samples.

Which Doctor Treats Poliomyelitis?

Poliomyelitis is diagnosed and treated by specialists in neurology, pediatric neurology, and infectious diseases, including internal medicine.