Polio

Overview of Polio

In many of the underdeveloped, developing, low-income and middle-income countries, the practice of childhood immunisations is almost absent due to the lack of adequate knowledge or poor facilities. These conditions pave way for numerous diseases that may debilitate a person for a lifetime. Polio is one such life-threatening disease.

Collaborative Polio-eradication initiatives have led to the drop of incidence rate by about 99% in the last 10 years (source: CDC reports). It is also said that nearly 80% of the current global population is now immunised against Polio. But the remaining 20% is either struggling with or has a high likelihood of acquiring the disease. Funds for polio immunisations should be increased in order to completely eradicate the disease and improve overall health standards worldwide.

What is Polio?

Polio or Polio myelitis is an infectious disease mediated by certain viral pathogens that causes muscle weakness and immobility. The disease gets its name from the Greek words “polio” meaning “grey” and “myelon” meaning marrow (indicates the spinal cord).

This implies that the disease mainly impacts the spinal cord and results in paralysis. But in various other cases, Polio has been found to affect the gastrointestinal tract and the muscles.

In all three cases, the person is crippled for life and cannot move without aids. Past incidences have shown that nearly 2-5% of children and 15-30% adults die from the disease.

What are the main causes of Polio?

Polio is caused by the Poliovirus, which is a member of the Enterovirus subgroup, that belong to the Picornaviridiae family. The Picornaviruses are tiny, ether-sensitive viruses with an RNA genome. Three distinct Poliovirus serotypes have been identified so far namely- P1, P2 and P3. It must be noted in this regard that immunization against one serotype does not provide protection against the remaining two serotypes. Separate immunizations for all three serotypes are necessary.

The general factors that increase the risks of contracting the disease are given below-

• Immune suppression
• Malnourishment
• Vitamin deficiency
• Tonsillectomy
• Physical activity following exposure to the poliovirus
• Injury to the skeletal muscles due to the injection of vaccines (or other therapeutic agents)
• Pregnancy
• Travelling to an area where a recent epidemic outbreak has occurred
• Taking care of a polio-patient or living with a polio patient
• Being in a laboratory having ample specimens of poliovirus

Pathogenesis of Polio

The poliovirus enters the body mainly through the mouth. It starts propagating right from the site of implantation in the pharynx and the gastrointestinal tract. The duration of the incubation period is normally 6-20 days. In some cases, it might range from 3-35 days.

Before the onset of the illness, the virus is normally found in the stool and the throat. After a week of the onset, only trace amount of virus is present in the throat, while more viruses are excreted through the faecal matters.

This condition lasts for several weeks. The virus gradually attacks the local lymphoid tissue, enters the circulating bloodstream and finally infects the cells of the Central Nervous System. This is followed by the multiplication of the poliovirus in the motor neurons of two primary sites-

• The anterior horn
• The brain stem

This results in massive cell destruction and gives rise to a wide range of clinical manifestations.

How does the poliovirus spread?

The poliovirus spreads through the following transmission routes-

• Faecal-oral route
• Oral-oral route
• Respiratory droplets or throat secretions of the infected person
• Contaminated foods and drinks
• Unclean and contaminated utensils
• Unhygienic habits like having food without washing hands
• Putting contaminated hands or objects inside the mouth (common in babies)

What are the main clinical manifestations?

In 95% of the cases, Polio is asymptomatic, that is does not have visible symptoms. Nearly 4-8% patients exhibit the following symptoms-

• Sore throat
• Fever
• Nausea
• Vomiting

The remaining 1-2% of the infected individuals may develop non-paralytic aseptic (viral) meningitis. The main features in this condition are- stiffness or immobility of the head, neck, back, arms and limbs.

In less than 1% of the cases, “flaccid paralysis’ is observed, wherein the patient is left with permanent weakness of the arms, limbs or both.

What are the main types of Polio?

Based on the severity of the symptoms, Polio can be classified into two types-

Non-paralytic polio: It is a less severe form of polio and is also known as abortive polio, since it is partly recoverable. The symptoms that last for 1-10 days include-

• Sore throat
• Fever
• Headache
• Meningitis
• Vomiting
• Fatigue

Paralytic polio: It is the more serious type and is observed in 1% of the cases. It can lead to permanent disability. The general symptoms in this case are-

• Muscle pain and spasm
• Loss of reflex
• Loose and hanging limbs (unilateral or bilateral)
• Sudden onset of paralysis
• Deformities in limbs, ankle, feet and heels

Based on the parts affected, polio can be categorised into three types-

• Spinal polio: In this case, the virus infects the motor neurons of the anterior horn cells or the ventral gray matter in the spinal column. Hence this condition impacts the movement of the trunk and limbs, as well as the intercoastal muscles.
• Bulbar polio: Here, weakening and destruction of the muscles supplied by the cranial nerves occurs. The nerves that are mainly affected in this disease are the glossopharyngeal nerve, vagus nerve, accessory nerve, trigeminal nerve and the facial nerve. The main symptoms are-problems in breathing, speaking, swallowing and encephalitis in some cases.

Diagnosis, treatment, & prevention

The following diagnostic tests are essential for determining the occurrence and severity of the disease-

• Stool culture
• Swab test
• Cerebrospinal fluid analysis
• White Blood Cell count
• Protein level
• Oligonucleotide mapping

In the present scenario, the treatment of Polio has not been devised.  The focus of the treatment is chiefly in providing symptomatic relief and preventing the occurrence of complications. The supportive treatment encompasses the administration of analgesics (pain reliever medications), physical therapy (physical exercises in order to prevent loss of muscle function and deformity), and portable ventilators (to help in breathing).

Prevention of the disease can be done by vaccination. There are two forms of vaccination OPV – Oral Polio vaccine (administered orally) and IPV- Inactivated Polio vaccine (an injectable form of the vaccine).