Infectious Diseases

Updated 19 May 2015


Polio is caused by a virus belonging to the family Picornaviridae.


  • Polio is an illness caused by a virus of the family Picornaviridae.
  • Although now very uncommon in the Western world, there continues to be a threat that it might get out of control.
  • The virus will most often cause a minor illness with symptoms similar to an upper respiratory tract infection, but it can cause an aseptic meningitis, and, more seriously, spinal cord inflammation resulting in paralysis.
  • Polio leaves a significant number of people paralysed in one or more limbs.
  • There is no specific treatment for polio, but it can effectively be prevented by vaccination.


Polio, strictly speaking called poliomyelitis, is a viral infection which has a wide range of signs and symptoms.

These can range from minor, flu-like illnesses, to weakness and paralysis of various muscle groups.

Alternative names

Infantile paralysis; Acute anterior poliomyelitis


Polio is caused by a virus belonging to the family Picornaviridae. There are three different types: 1, 2 and 3. Polio was an important disease in temperate Western countries (Europe and the USA) during the last part of the nineteenth century and well into the twentieth century, until a vaccine was developed in the 1950s. The disease is now very rarely seen (a consequence of importation) in these countries.

However, polio remains a serious public health threat in the developing world to this day. Despite a global vaccination campaign by the WHO, there are still pockets of the disease in a few countries in Asia and Africa where there is cultural or political resistance to vaccination, or where vaccination programmes have broken down due to war or other upheaval.

In South Africa, there is an ongoing intensive polio vaccination programme and no cases have been identified since the 1980’s. However, polio outbreaks occurred in neighbouring Angola and Namibia in the early 1990’s and again in Namibia in 2006.

Who gets it and who is at risk?

Where there are poor socio-economic circumstances and poor sanitation and hygiene, the virus is potentially present year-round. If polio is endemic, people can acquire a natural immunity since they are exposed to it as children, often getting the mild form of the illness. In these circumstances, the paralytic form of polio is usually seen only in children less than five years old. In outbreaks in naïve (previously unexposed) populations, the disease will affect all age groups.

The disease spreads primarily through the "faecal-oral route". In the context of an outbreak this usually means that infected faeces has contaminated the drinking water supply. It can also spread within households through poor hygienic practices that allow faeces to contaminate food or drink.

Symptoms and signs

Polioviruses cause the disease "poliomyelitis" when they spread from the gut to the central nervous system (brain and spinal cord).

At least 80 to 90% of cases of infection with the polio virus result in a minor illness. These are usually in young children and the illness is mild, with a sore throat, slight fever, malaise, headache and vomiting which develops three to five days after exposure to the virus. The child recovers within 24 to 72 hours.

The major illness may follow several days of appearing to be well after a minor illness. However, it often occurs with no signs of previous illness at all, particularly in older children and adults.

The incubation period is seven to 14 days. The first sign is often fever, followed by a severe headache and a stiff neck. This is in fact a form of meningitis, and is called an aseptic meningitis because it is not caused by a bacteria. There may also be muscle and back pain or muscle spasms and sometimes increased sensitivity to pain when the skin is touched and pins and needles in the arms and legs.

The disease may stop at this stage and the person recovers. If the disease progresses, there is gradually progressing weakness or paralysis of various muscle groups. This is often only on one side of the body – asymmetric. The paralysis is what is called flaccid, meaning floppy. This is important because other forms of paralysis are often rigid.

There is no loss of sensation – again important because this distinguishes polio from other forms of paralysis. Frighteningly, the disease can involve the part of the brain stem where cranial nerves originate and where the centre that controls respiration (breathing) is found. In these cases, signs such as difficulty swallowing or respiratory paralysis occur.


Asymmetric flaccid paralysis in the arms and/or legs without any signs of loss of sensation during an acute illness with fever in a child or young adult almost always indicates polio infection.

The virus can be isolated from the throat and/or faeces which can confirm the diagnosis.

Polio must be distinguished from diseases such as Guillain-Barré syndrome or infection with other viruses related to the polioviruses such as the coxsackie and echoviruses which also rarely cause paralysis. In the case of Guillain-Barré syndrome, the clinical picture is slightly different and the cerebro-spinal fluid shows a different cell count and chemistry when examined. In South Africa all cases of “acute flaccid paralysis” must be notified to the Department of Health and be investigated to exclude polio.


The short answer is yes. Active immunisation is recommended for all children and infants. In South Africa, immunisation against polio is part of the normal vaccination schedule and periodically, there are specific campaigns in which booster doses are given to children and adults.

Travellers intending visiting areas where polio is active should obtain a booster vaccination 10 days or more before departure at a travel clinic or through a government health facility.

The World Health Organisation has targeted polio as an illness which it would like to eradicate in the early part of this century, through global vaccination. However, their efforts in Africa are being countered by the problems of gaining access to the many countries which are disrupted by continuing wars.


There is no specific treatment for polio. The mild illness is treated by relieving the symptoms with painkillers and anti-fever medication and fluids.

When a child or adult has muscle weakness or paralysis, they need rest on a firm bed, with painkillers and the application of warm packs to the affected muscles which will also help relieve pain.

A common complication of the paralytic form of polio is the inability to pass urine. This can be helped by certain drugs or by using a catheter periodically to empty the bladder.

If the muscles of respiration are affected then the person will need to be ventilated.

During the recovery phase physiotherapy is very important to prevent wasting of the muscles and contraction of the tendons which could result in deformity and loss of use.


In the mild illness, recovery is complete. Recovery is also complete in the more serious form of the illness with aseptic meningitis but without paralysis.

Death occurs in a small percentage of cases of paralytic poliomyelitis, the highest risk being in those with respiratory paralysis. In those who recover, a high proportion of persons are left with some degree of disability.

Most function returns within the first six months after the illness, but improvement may be seen for around two years.

A rare complication is called postpolio syndrome and is seen in people who have suffered the paralytic form of the illness. This can occur many years after the attack and is seen mainly in older and more severely affected people. The symptoms and signs of this are muscle fatigue and decreased endurance capacity. This can be accompanied by weakness, twitching of the muscles (fasciculation) and wasting in selected muscles.

When to see your doctor

If you live in an area or have travelled to an area where polio still occurs and you or your child has an illness which seems similar to the more serious forms of polio, then see your doctor immediately.

Reviewed by Dr J Yeats, MBChB, FC Path(SA)viro

Updated August 2006


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