Polio is common usage for poliomyelitis which is an infectious disease caused by poliovirus resulting in acute illness, paralysis and sometimes death and in residual paralytic deformities.
Pathophysiology of Polio
Poliovirus is a type of enterovirus, a group of RNA viruses that colonize the gastrointestinal tract. Three serotypes of poliovirus have been identified. PV1 is the most commonly encountered form, and the one most closely associated with paralysis.
The incubation period ranges from 3 to 35 days[avg-20 days].
Poliomyelitis usually spreads through the fecal-oral route. After inital infections, virus particles are excreted in the feces for several weeks. The disease is transmitted, by ingesting contaminated food or water.
It is occasionally transmitted via the oral-oral route.
Increased risk of getting polio infection is seen in following people
- Very young
- Pregnant women
- Immunocompromised
- Unimmunized people
- traveling to endemic places
- Living with someone infected with polio
- Working in a laboratory where live poliovirus is kept
The virus enters the body through the mouth and infects the first cells with which it contacts — the pharynx and intestinal mucosa. The virus divides within gastrointestinal cells for about a week, from where it spreads to the tonsils, the intestinal lymphoid tissue including the M cells of Peyer’s patches, and the deep cervical and mesenteric lymph nodes and is subsequently absorbed into the bloodstream and spreads.
The virus may invade the central nervous system and cause a self-limiting inflammation of the meninges.
The poliomyelitis virus, once established in the central nervous system, has a special affinity for the anterior horn cells of the spinal cord and for certain motor nuclei in the brain stem.
The earliest visible change is chromatolysis of the Nissl substance in the cytoplasm of the nerve cell. This is followed by inflammatory polymorphonuclear and cells, at first in the perivascular regions and the diffusely in the grey matter.
In the irreversible case chromatolysis progress the cell nucleus shrinks and the necrotic cell is removed by neuronophagia.
As a result of the destruction of the nerve cells in the anterior horn, the peripheral nerve degenerates and the muscle supplied by it atrophy. The extent of muscle degeneration depends on the amount of nerve involved.
Types of Polio
Non-paralytic polio
It is also called abortive poliomyelitis, leads to flu-like symptoms that last for a few days or weeks. These include:
- Fever
- Sore throat
- Headache
- Vomiting
- Fatigue
- Back and neck pain
- Arm and leg stiffness
- Muscle tenderness and spasms
- Meningitis
Paralytic polio
Paralytic polio affects only a small percentage of those invaded by the polio virus. The virus enters motor neurons where it replicates and destroys the cells in the spinal cord, brain stem, or motor cortex of the brain.
The presentation is similar to non- paralytic polio later progress to more serious symptoms such as:
- a loss of muscle reflexes
- severe muscle pain and spasms
- loose or floppy limbs that are often worse on one side of the body
- loss of superficial and deep reflexes, paresthesia (pins and needles), irritability, constipation, or difficulty urinating
Paralysis generally develops one to ten days after early symptoms begin, progresses for two to three days, and is usually complete by the time the fever breaks
Depending on the involvement, the paralytic polio may also be classified as:
Spinal poliomyelitis
The involvement of motor neurons in the spinal cord that causes paralysis in the arms and legs, and breathing problems. The extent of spinal paralysis depends on the region of the cord affected.
Bulbar poliomyelitis
- The virus affects the neurons in bulbar region of brain stem affecting sight, taste, swallowing, and breathing.
- Pulmonary edema and shock are also possible and may be fatal.
Bulbospinal poliomyelitis
- Approximately 19 percent of all paralytic polio cases have both bulbar and spinal symptoms
Clinical Course of Paralytic Poliomyelitis
Acute stage
- Febrile phase
- 4 to 7 days
Preparalytic stage
- Fever, malaise and nausea or vomiting.
- Neck stiffness
- Irritable and complains of pain in the trunk or limbs.
Paralytic stage
- Usually supervenes usually on the third of fourth day but may appear at any time during the major illness.
- Spinal or bulbar type paralysis.
Convalescent stage
- Starts immediately after the acute stage of major illness and ends when no further significant recovery in muscle power is anticipated.
Residual stage
Significant increase in reliable muscle chart recordings seldom occurs later than 2 years after the onset of poliomyelitis, but functional improvement may continue for several years especially in young children.
Diagnosis
Symptoms like acute febrile illness, as neck and back stiffness, abnormal reflexes, especially in setting of outbreak should lead to suspicion of polio and investigated accordingly.
Laboratory studies include
- Recovery of poliovirus from a stool sample or a swab of the pharynx.
- Antibodies to poliovirus in the blood of infected patients.
- Lumbar puncture and CSF analysis
- Increased WBCs (lymphocytes)
- Mildly elevated protein level.
- Detection of virus [rare]
- Isolation of poliovirus
Treatment of Polio
Because there is no cure for polio once a person develops the virus, treatments are focused on increasing comfort, managing symptoms, and preventing complications. This can include bed rest, antibiotics for additional infections, painkillers, ventilators to help breathing, physiotherapy, moderate exercise, and a proper diet.
Acute cases are admitted and provided supportive treatment. The extent of support would vary with presentation. For example, in case of respiratory difficulty, respiratory support is provided.
Convalescent phase
- Splint to eliminate deformity tendencies
- Restore joint mobility
- To train the coordination of recovering muscles.
- Muscle strengthening exercises at a later stage
Post-polio syndrome
It describes a cluster of symptoms occurs several years after polio has passed. On average, post-polio syndrome occurs 35 years after the infection.
Signs and symptoms include:
- Progressive muscle and joint pain
- Muscle atrophy (shrinking)
- Exhaustion for no reason
- Swallowing and breathing difficulties
- Suffering in colder temperatures
- Sleep-related problems such as apnea (stopping breathing)
- Concentration and memory difficulties
- Mood swings and depression
Post-poliomyelitis syndrome is a slow, progressive disease. There is no cure, but it is not infectious or contagious.
Prevention of Poliomyelitis
There are two vaccines available to fight polio:
Inactivated poliovirus (IPV)
IPV consists of a series of injections that start 2 months after birth and continue until the child is 4-6 years old. The vaccine is made from inactive poliovirus. It is very safe and effective and cannot cause polio. It provides full protection against polio.
Oral polio vaccine (OPV)
OPV is created from a weakened form of poliovirus. It is low-cost, easy to administer, and gives an excellent level of immunity. However, in very rare cases, OPV has been known to revert to a dangerous form of poliovirus, which is able to cause paralysis.