Poliomyelitis may manifest with a range of symptoms. These may vary according to severity.

For example, a large number of infected individuals have no apparent signs of infection and are thus termed asymptomatic. These patients however may transmit the virus by shedding it in their stools.

The symptoms of polio may be outlined as subclinical infection, non paralytic polio and so forth. (1-5)

Subclinical infection

This is seen in 95% of individuals infected with polio. In places where outbreaks are common, children with this type of infection are called the “reservoirs” of polio since they inadvertently shed the virus in their stools that gets transmitted to other exposed individuals.

There is a general feeling of illness or malaise, red and sore throat, fever (mild), headache and sometimes vomiting. The symptoms may last for less than 72 hours.

Non-paralytic polio

Non paralytic polio may last for a week or two. It is characterized by:

• back pain
• muscle stiffness
• headache
• fatigue
• irritability
• diarrhea
• pain over the calf muscles
• mild to moderate fever
• muscle spasm and pain
• neck pain and stiffness
• pain in front of the neck or in the back, arms, abdomen and legs
• skin rashes
• nausea with vomiting

Paralytic polio

In less than 1% of polio infections the virus may invade the nerves of the anterior horn of the spinal cord. It specifically affects the nerves that control motor movements.

If the spinal cord is affected closer to the brain or if the lower part of the brain called the brain stem is affected there may be severe paralysis of the respiratory muscles making it difficult to breathe. This may be life threatening.

In the lower parts of the spinal cord the infection may lead to permanent muscle weakness of the lower limbs and paralysis and disability. Thus the level of spinal cord that is affected determines the outcome of the illness.

It is called spinal (commonest of paralytic polios), bulbar (seen in 2% of paralytic cases) or spinobulbar or bulbospinal (seen in 19% of paralytic cases).

Spinal paralysis affects the spine and leads to paralyzed legs. This is seen in 80% of the paralytic cases. The paralysis of the legs may be patchy and non-uniform. In bulbar polio the brain is affected.

Paralytic polio begins with a fever for 5 to 7 days before any other symptom.

There may be:

• abnormal sensation in the paralyzed area
• bloating of the abdomen
• constipation
• difficulty in urinating
• difficulty breathing
• drooling
• headache and irritability
• muscle pain and stiffness in the back, neck and legs
• weakness over one side that comes in quickly and worsens into paralysis
• simple touch may be painful
• there may be difficulty in swallowing

Post-polio syndrome

After resolution of the symptoms of polio the patient may develop post-polio syndrome (PPS). This may appear 30 to 40 years after the initial infection.

There is severe muscle weakness and paralysis of the previously unaffected muscles. It is rarely fatal but has a slow and unpredictable course. PPS is not infective.