Why does polio affect the legs?

Polio also called poliomyelitis is an infectious disease caused by any one of the three types of polio virus. Between 70% and 95% of people infected with poliovirus don’t have symptoms. Of those with symptoms, most people have the mildest form (abortive poliomyelitis) and flu-like symptoms. The most severe symptoms are seen with paralytic polio or post-polio syndrome, causing serious problems that affect the brain and nerves, and weakness in your muscles (paralysis), usually in the legs. In about 1 in 200 cases, people who have polio become paralysed. The paralysis usually affects the legs and is permanent. Lets take a look at why polio affects the legs.

✅ Facts about polio

• Polio is caused by any one of the three types of polio virus. There are three variations of poliovirus, called wild poliovirus type 1, 2 and 3 (WPV1, WPV2 and WPV3)
• Cases of polio still exist in some parts of the world today. Polio vaccination is essential to the eradication effort. Polio is still a significant problem in Afghanistan, Nigeria and Pakistan, and there’s a potential risk of infection in other parts of Africa and some Middle Eastern countries
• Two types of vaccine are available: An inactivated poliovirus vaccine (IPV) and a live attenuated oral polio vaccine (OPV). Inactivated polio vaccine is injected intramuscularly and recommended by the CDC and the NHS. Oral poliovirus vaccine is still used in endemic areas such as Afghanistan and Pakistan. Experts now recommend that the OPV not be given and that only IPV be used
• People at high risk of infection with the poliovirus are young children under 5 years of age, pregnant women, elderly people, people with a weakened immune system and people travelling to an area where polio is common or where an outbreak has recently occurred

📝 How does polio spread?

The poliovirus is spread when food, water or hands contaminated with faeces, throat or nasal secretions of an infected person enter the mouth of an uninfected person.

A person may develop symptoms within 3 to 21 days of coming into contact with the virus and will be most infectious 7 to 10 days before and after the beginning of symptoms.

People remain infectious for as long as the virus continues to be excreted in their faeces, which may continue for up to 6 weeks. Typically, the virus remains in the throat for 1 to 2 weeks.

📝 What happens when polio attacks the body?

Nerve cell (neuron)

The nervous system is made up of small units called neurons or nerve cells. A typical neuron has three main parts; a cell body (soma), dendrites (branching fibres) and a single axon. This unit is often described as a tree:

• The axon is a tree root (where neurons talk to each other through an electrical message)
• The soma is a tree trunk (where the DNA lives in the nucleus)
• The dendrites are tree branches (neurons receive messages from other cells)

A myelin sheath covers neurons to insulate and protect them.

Why are the legs commonly affected by polio?

When poliovirus infects your body, it affects a specific type of nerve cell called motor neurons. Motor neurons carry messages (electrical impulses) between your brain and your muscles, directly controlling all voluntary muscle movements throughout the body, including walking, breathing and fine motor skills, like writing and drawing. It is the final pathway for the brain to initiate movement by stimulating contractions.

Poliovirus particularly affects the motor neurons in the spinal cord. A polio infection often damages or destroys many of these motor neurons, preventing movement, particularly in leg muscles, significantly affecting your ability to walk. This could lead to falls and other complications.

📊 Types of polio

Poliovirus infection is classified into four main types based on the severity of the disease and its symptoms. As mentioned earlier the legs are generally affected by paralytic polio and post-polio syndrome. Lets take a deeper look into the other symptoms of polio.

Symptoms of abortive poliomyelitis

Abortive poliomyelitis symptoms are a mild form of polio, affecting most people that contract the virus. Flu-like symptoms start three to seven days after getting infected and last a few days. Symptoms of abortive poliomyelitis include:

• Fatigue
• Fever
• Headache
• Vomiting
• Diarrhoea or constipation
• Sore throat

Symptoms of non-paralytic poliomyelitis

Non-paralytic poliomyelitis starts with the same symptoms as abortive poliomyelitis, then symptoms progress onto:

• Neck stiffness
• Pain or pins-and-needles in your arms and legs
• Severe headaches
• Sensitivity to light

Symptoms of paralytic poliomyelitis

Paralytic poliomyelitis starts out with symptoms similar to abortive poliomyelitis or non-paralytic poliomyelitis. The polio virus then goes onto attack the brain and spinal cord, causing paralytic poliomyelitis. Symptoms include:

• Sensitivity to touch
• Muscle pain
• Spinal poliomyelitis, preventing movement of arms or legs or both (paralysis)
• Bulbar poliomyelitis, which makes it hard to breathe, swallow and speak. If the breathing muscles are affected, it can be life threatening
• Bulbospinal poliomyelitis has symptoms of both spinal and bulbar polio

Post polio syndrome (PPS)

Most people who have had polio fight off the infection without even realising when they are infected. Other people however go on to develop post-polio syndrome symptoms that appear decades after the initial polio illness. It is not clear why some polio survivors develop post-polio syndrome while others do not.

It has been suggested that in some people, after initial infection, the remaining nerves and muscles in the body have worked harder to compensate over the years. This has resulted in nerves becoming exhausted and even dying, forcing the nerves and muscles that are left to work even harder. This gradual change can explain why it can take years for post-polio syndrome symptoms to appear.

Symptoms of post-polio syndrome usually develop gradually over time, these include:

• Extreme tiredness
• Progressive muscle weakness
• Muscle atrophy (muscles shrinking in size)
• Muscle and joint pain

These symptoms can be debilitating and affect quality of life severely.

🏥 How post-polio syndrome is treated

There is no cure for post-polio syndrome, but support and a range of treatments are available from your healthcare provider to help manage your symptoms and improve your quality of life.

Some of the ways that symptoms of post-polio syndrome may be managed include:

• Physical therapy/physiotherapy to help with any movement problems and build up muscle strength
• Devices such as splints and braces to support weak limbs or joints
• Mobility aids such as walking sticks or scooters
• Weight control and healthy eating – to avoid putting unnecessary strain on muscles and joints
• Medication for muscle or joint pain
• Psychological support

🩺 When should I see my healthcare professional?

Contact your healthcare provider if you’ve been exposed to polio and have symptoms, especially if you aren’t vaccinated. If you have questions about getting vaccinated or getting your child vaccinated speak to a healthcare professional.

📝 Conclusion

Polio is a disease that severely affects motor neurons in the body, causing a range of symptoms, particularly problems affecting the legs. However, between 70% and 95% of people infected with poliovirus don’t have symptoms. The most severe symptoms are seen with paralytic polio or post-polio syndrome, usually in the legs. There is no cure for PPS, but supportive therapies can help you manage the condition. Always speak to your healthcare provider if you are experiencing symptoms affecting the legs after a polio infection.

Sources

• Post-polio syndrome – Symptoms & causes – Mayo Clinic
• Polio: Virus, Causes, Symptoms, Transmission & Treatment
• Post-polio syndrome – NHS
• Polio – NHS
• Poliomyelitis
• NaTHNaC – Poliomyelitis
• Polio – NHS inform
• Disease factsheet about poliomyelitis