Overview

Poliomyelitis, commonly known as polio, is a highly infectious viral disease caused by the poliovirus. This disease primarily affects the nerves in the spinal cord or brain stem. In severe cases, it can cause paralysis, difficulty breathing, and even death.

Polio spreads through fecal-oral transmission, often through contaminated water, food, or contact with infected individuals. Most people infected with polio experience no symptoms or mild, flu-like illness. However, a small percentage can develop severe paralysis.

Vaccination is the most effective way to prevent polio. There is no cure for the disease, so preventing infection through immunization is crucial. The U.S. Centers for Disease Control and Prevention (CDC) advises that vaccinated adults who plan to travel to areas where polio is spreading should receive a booster dose of the inactivated poliovirus vaccine (IPV), which provides lifetime immunity.

Prevalence

Historically, polio outbreaks caused significant global health concerns, leading to widespread fear and disability. Thanks to global vaccination efforts, polio cases have decreased by over 99% since 1988.

There are three types of poliovirus: type 1, type 2, and type 3. Types 2 and 3 have been eradicated. However, type 1 poliovirus still circulates in some parts of the world, particularly in Pakistan and Afghanistan, due to challenges in vaccination coverage and healthcare infrastructure.

Polio has been effectively eradicated in the United States since the 1970s. No recent cases of naturally occurring polio have been reported within the country.

Global eradication of polio remains a key public health goal. Continued vaccination campaigns and surveillance programs are crucial for achieving this objective.

Symptoms

In most instances, the poliovirus causes no symptoms or only mild, flu-like symptoms. However, a small percentage of infections (less than 1%) lead to paralysis, a severe complication. Signs and symptoms of polio can vary depending on the severity of the infection.

Abortive Polio

Abortive polio is the mildest form of polio. It causes flu-like and intestinal symptoms that typically last a few days and do not result in long-term issues. Symptoms include fever, decreased appetite, nausea/vomiting, sore throat, malaise, constipation, and abdominal pain.

Non-paralytic Polio

Non-paralyic polio is similar to abortive polio but with more severe symptoms and a longer duration. It may cause aseptic meningitis, which is a swelling of the area around the brain. It may require hospitalization. Symptoms include:

• Pain in the muscles of the neck, trunk, arms, and legs
• Stiffness in the neck and along the spine

Paralytic Polio

Paralytic polio is the most severe form of polio. It occurs when the poliovirus attacks the brain and spinal cord, potentially leading to paralysis. Depending on the affected areas, it can be classified as spinal polio, bulbar polio, or bulbospinal polio. Symptoms include muscle weakness, severe constipation, muscle wasting, weakened breathing, trouble swallowing, and muscle paralysis.

Less than 1% of polio cases result in paralytic polio.

Polioencephalitis

Polioencephalitis is a rare type of polio that primarily affects infants. It causes swelling of the brain.

Post-Polio Syndrome

Post-polio syndrome occurs when symptoms of polio return years after the initial infection. This can happen to anyone who has had polio in the past, even if they fully recovered. Symptoms may include muscle weakness, fatigue, and pain the muscles and joints

General Symptoms of Polio

Poliovirus is highly infectious, with an incubation period typically ranging from 7 to 10 days, but it can vary from 4 to 35 days. The virus enters the body through the mouth and multiplies in the intestine before invading the nervous system. Initial symptoms include:

• Fever
• Fatigue
• Headache
• Vomiting
• Stiffness in the neck
• Pain in the limbs

In most cases, these symptoms last for 2 to 10 days, and recovery is usually complete. However, in a small proportion of cases, the virus causes paralysis, typically in the legs, which is often permanent. Paralysis can occur rapidly, sometimes within hours of infection. Among those paralyzed, 5-10% die when their breathing muscles become immobilized.

Polio primarily affects children under 5 years of age, but unvaccinated individuals of any age can contract the disease. There is no cure for polio, but it can be prevented through vaccination. The polio vaccine, given multiple times, can protect a child for life.

Transmission

Polio is caused by the poliovirus, a member of the Picornaviridae family. The virus is primarily transmitted through the fecal-oral route, entering the body via contaminated food, water, or direct contact with an infected person.

Once inside the body, the poliovirus multiplies in the intestines and can spread to the bloodstream and lymphatic system. It then targets motor neurons in the spinal cord, causing inflammation and damage. This damage interrupts the signals sent from the brain to the muscles, leading to muscle weakness, paralysis, and potentially fatal respiratory failure.

There are three distinct serotypes of the poliovirus (types 1, 2, and 3). Infection with one type does not provide immunity against the others, making vaccination against all three crucial for prevention.

Risk Factors

Several factors can increase the risk of contracting polio:

• CIncomplete Vaccination: Individuals who have not received the polio vaccine or have incomplete vaccination schedules are at higher risk.
• Poor Sanitation: The virus spreads primarily through the fecal-oral route, so those living in areas with inadequate sanitation and hygiene practices are at increased risk.
• Travel to Endemic Regions: Visiting regions where polio is still endemic, such as Pakistan or Afghanistan, or where outbreaks have occurred, increases the risk of exposure.
• Immunocompromised Individuals: People with weakened immune systems, such as those with HIV/AIDS or those undergoing immunosuppressive therapy, may be at increased risk of developing more severe forms of polio if infected.
• Young Children: Children under the age of 5 are most susceptible to poliovirus infection, especially if they have not been vaccinated.
• Seasonal Outbreaks: Polio outbreaks often occur during warmer months, which may increase the risk of transmission due to factors such as increased population movement and outdoor activities.
• Crowded Living Conditions: Those living in crowded conditions, such as densely populated urban areas, are at higher risk of polio transmission due to close contact with infected individuals.
• Close Contact with Infected Individuals: Close contact with someone infected with the poliovirus, particularly in settings where hygiene practices are poor, increases the risk of transmission.

Diagnosis

In the United States, healthcare providers who suspect a patient has polio generally hospitalize the patient right away and may diagnose through a combination of clinical evaluation, lab testing, and medical history, including vaccination history and history of any recent travel.

Healthcare providers assess symptoms such as acute onset of muscle weakness or paralysis, conduct physical exams to evaluate reflexes and muscle strength, and may perform lab tests such as viral culture or polymerase chain reaction (PCR) testing on samples of throat swabs, stool, or cerebrospinal fluid to detect the poliovirus, keep in mind that poliovirus is most likely to be detected in stool specimens.

Differential diagnosis is also considered to rule out other conditions with similar symptoms. Additionally, imaging studies may be used to assess nerve damage or complications.

Treatment

Polio has no cure and does not have specific treatment. However, arm or leg weakness resulting from polio can be alleviated and long-term outcomes potentially improved through physical or occupational therapy, particularly if initiated early during the illness.

Healthcare providers are encouraged to consult with neurology and infectious disease specialists to explore potential treatments and advise on specific interventions tailored to individual cases.

If you suspect either yourself or a family member of experiencing symptoms of polio, it is important to immediately contact your healthcare provider or seek assistance at an emergency room.

Prevention

Vaccination is the most effective way to protect against polio. In the United States, the following vaccine is offered for the prevention of polio:

Inactivated Poliovirus Vaccine (IPV):

IPV is a vaccine that provides immunity against all 3 serotypes of the poliovirus (type 1, type 2, and type 3). It is administered as a series of injections given at 2 months, 4 months, 6-18 months, and 4-6 years of age, and can be administered as a shot in the arm or leg, is very safe, and protects against paralysis.

IPV is part of the routine childhood immunization schedule in the U.S. and is also recommended for certain adults who may be at increased risk of exposure to poliovirus, such as travelers to areas where polio is endemic.

In addition to vaccination, other prevention measures for polio include the following:

• Improving proper sanitation and hygiene practices, including access to clean water and proper waste disposal, can help reduce the risk of poliovirus transmission.
• Active surveillance for polio cases, timely detection of outbreaks, and rapid response with vaccination are important for controlling outbreaks and preventing the spread of poliovirus.