Post-polio syndrome

Affecting people who have recovered from polio, post-polio syndrome is a cluster of disabling signs and symptoms that appear decades — between 10 and 40 years — after the initial illness.

Common signs and symptoms include:

• New muscle weakness in limbs
• Breathing or swallowing problems
• Sleep-related breathing disorders, such as sleep apnea
• Decreased tolerance of cold temperatures
• General fatigue and exhaustion with minimal activity
• Muscle and joint pain

Virus target tissues

Polio has also been divided into several types, depending on which part of the body is affected.

Spinal polio
This type of the disease, the most common form, attacks nerve cells in the spinal cord and may cause paralysis of the muscles in arms, legs, and respiratory muscles. Children under the age of 5 are most likely to become paralyzed in a single leg, whereas paralysis of both arms and legs is more common in adults. An affected limb becomes floppy and poorly controlled — the condition of acute flaccid paralysis (AFP).

Bulbar polio
During this type of infection the virus affects the motor neurons in the brain, where the centers of certain nerves, called the cranial nerves, are located. These nerves are involved in the patient’s ability to see, hear, smell, taste and swallow.  

Bulbospinal polio
This is a combination of both bulbar and spinal paralytic polio. It usually leads to paralysis of arms and legs and may also affect breathing, swallowing and heart function.

The cause of poliomyelitis, ways of transmission

The cause of poliomyelitis is a virus called Poliovirus, which resides exclusively in humans. It is transmitted primarily through the fecal-oral path of infection, especially in areas where ventilation and sanitation systems are inadequate. Several studies have proven that it also can be transmitted through contaminated water and food. Although people carrying the virus are most contagious seven to 10 days before and after the signs and symptoms appear, they can spread the virus for weeks thereafter through their feces.

Pathogenesis of poliomyelitis

Once the poliovirus invades a patient’s body, it multiplies in throat lining and intestinal tract, and then travels to the central nervous system through blood and lymph. While the virus moves along nerve fibers, it damages the motor neurons that normally carry messages between the patient’s brain and muscles.
The mechanism by which the virus does harm after reaching the nervous system has been well studied: In order to compensate for the missing neurons, the remaining nerve cells spread new fibers. This places added stress on the nerve cell body, which has to nourish the additional fibers. Over time, this stress may be more than the neuron can handle.