Polio, also called poliomyelitis or infantile paralysis, is a crippling and potentially deadly infectious disease which mainly affects young children, caused by the poliovirus. It is a contagious viral illness that in its most severe form causes nerve injury leading to paralysis, difficulty breathing and sometimes death.
There are three types (PV1, PV2 and PV3) of polioviruses identified. These types are antigenically distinct strains of viruses. Infection or immunity to one type does not protect against the other two types, however, if immunity is established to one or all of the three strains, immunity is lifelong. All three are extremely virulent and produce the same disease symptoms. PV1 is the most commonly encountered form and the one most closely associated with paralysis.
Polio is a serious viral infection that used to be common worldwide. It's rare nowadays because it can be prevented with vaccination.
Infectious diseases are generally believed to arise from the interplay of various developments such as humans' settlement in urban structures, crowding that causes poor hygiene, food shortages enhancing populations' morbidity, and the domestication of animals.
The exact origin of the disease is not known, but based on the characteristics of the disease, epidemiologists are able to hypothesize how the disease has evolved and spread. Because the disease requires a human host and does not survive outside the human body for longer than one to two weeks, the disease could only have developed when humans started to settle in larger agglomerations. Various skeletons have been found with deformations similar to polio but the most widely-referenced indication of polio has been an Egyptian stele depicting Doorkeeper Roma with one leg skinnier and deformed, both typical symptoms of paralytic polio.
Poliovirus is usually spread from person to person mainly through infected faecal matter entering the mouth. In areas with poor sanitation, the virus easily spreads from faeces into the water supply, or by touch, into food. You can get infected with poliovirus if you have faeces on your hands and you touch your mouth. Also, you can get infected if you put in your mouth objects like toys that are contaminated with faeces.
Occasionally, one can get infected with the droplets launched into the air when an infected person coughs or sneezes.
Once the virus has entered an individual, it infects the cells of the throat and intestine, where it starts to multiply. The virus stays within the intestines, before spreading to other areas of the body. Eventually, the virus moves into the bloodstream where it can spread to the entire body.
People who don’t have symptoms can still pass the virus to others and make them sick.
There have been rare cases where polio has been caused by being vaccinated with a live version of the polio virus. This is no longer a risk because the vaccine used nowadays contains an inactive version of the virus.
Signs and Symptoms
Although polio can cause paralysis and death, the majority of people who are infected with the virus do not have any visible symptoms and may not be aware they have been infected.
About 95 percent of all cases are asymptomatic, and between 4 and 8 percent of cases are symptomatic.
Some people who develop symptoms from the poliovirus contract a type of polio that doesn't lead to paralysis (abortive polio). This usually causes the same mild, flu-like signs and symptoms typical of other viral illnesses.
Signs and symptoms, which can last up to 10 days, include:
Back pain or stiffness
Neck pain or stiffness
Pain or stiffness in the arms or legs
Muscle weakness or tenderness
These symptoms usually go away on their own.
This most serious form of the disease is rare. Initial signs and symptoms of paralytic polio, such as fever and headache, often mimic those of non-paralytic polio. Within a week, however, other signs and symptoms that affect the brain and spinal cord appear, which include:
Loss of reflexes
Paraesthesia (feeling of pins and needles in the legs)
Meningitis (infection of the covering of the spinal cord and/or brain) occurs in about 1 out of 25 people with poliovirus infection
Severe muscle aches or weakness
Loose and floppy limbs (flaccid paralysis), occurs in about 1 out of 200 people with poliovirus infection
Paralysis is the most severe symptom associated with polio because it can lead to permanent disability and death. Between 2 and 10 out of 100 people who have paralysis from poliovirus infection die because the virus affects the muscles that help them breathe.
There are also:
The virus attacks motor neurons in the spinal cord that causes paralysis in the arms and legs, and breathing problems.
The virus affects the neurons responsible for sight, taste, swallowing, and breathing.
The virus causes symptoms of both spinal and bulbar polio.
Post-polio syndrome is a cluster of disabling signs and symptoms that affect some people years after having polio (15 to 40 years later). Common signs and symptoms include:
Progressive muscle or joint weakness and pain
Muscle wasting (atrophy)
Breathing or swallowing problems
Sleep-related breathing disorders, such as sleep apnoea
Decreased tolerance of cold temperatures
Note that “poliomyelitis” (or “polio” for short) is defined as the paralytic disease. Only people with the paralytic infection are considered to have the disease.
Doctors often recognize polio by symptoms, such as neck and back stiffness, abnormal reflexes, and difficulty swallowing and breathing. To confirm the diagnosis, a sample of throat secretions, stool or a colourless fluid that surrounds your brain and spinal cord (cerebrospinal fluid) is checked for poliovirus.
Because there is no cure for polio once a person develops the virus, treatments are focused on increasing comfort, managing symptoms, speeding recovery and preventing complications.
Supportive treatments include:
Antibiotics for additional infections
Portable ventilators to assist breathing
Moderate exercise (physical therapy) to prevent deformity and loss of muscle function
As is the case with many other infectious diseases, people who get polio tend to be some of the most vulnerable members of the population. This includes the very young, pregnant women, and those with immune systems that are substantially weakened by other medical conditions.
Polio mainly affects children younger than 5. However, anyone who hasn't been vaccinated is at risk of developing the disease.
Additional risk factors for polio include:
travelling to places where polio is endemic or widespread
living with someone infected with polio
having a weak immune system
pregnant women are more susceptible to polio, but it does not appear to affect the unborn child
working in a laboratory where live poliovirus is kept
The most effective way to prevent polio is vaccination.
However, other methods of limiting the spread of this potentially fatal disease include:
avoiding food or beverages that may have been contaminated by a person with poliovirus
checking with a medical professional that your vaccinations are current
being sure to receive any required booster doses of the vaccine
washing your hands frequently
using hand sanitizer when soap is not available
making sure you only touch the eyes, nose, or mouth with clean hands
covering the mouth while sneezing or coughing
avoiding close contact with people who are sick, including kissing, hugging, and sharing utensils
as a precaution against infection, public swimming pools were often closed in affected areas during poliomyelitis epidemics
Be sure to receive a vaccination before travelling to an area that is prone to polio breakouts.
Almost all children (99 children out of 100) who get all the recommended doses of vaccine will be protected from polio.
There are two types of vaccine that can prevent polio: inactivated poliovirus vaccine (IPV) and oral poliovirus vaccine (OPV).
IPV consists of a series of injections that start 2 months after birth and continue until the child is 4 to 6 years old. This version of the vaccine is provided to most children in the U.S. The vaccine is made from inactive poliovirus. It is very safe and effective and cannot cause polio.
OPV is created from a weakened form of poliovirus. This version is the vaccine of choice in many countries because it is low in cost, easy to administer, and gives an excellent level of immunity.
Polio vaccinations or boosters are highly recommended for anyone who is not vaccinated or is unsure whether they are.
The World Health Organisation’s (WHO) aim is to eradicate polio completely and, if this happens, it will be only the third disease to have been beaten in this way, after smallpox and rinderpest.