Polio

Polio - What is Polio?

Polio (medically termed Poliomyelitis) is derived from Greek words Polio – meaning grey and myelon – meaning the spinal cord. The disease commonly affects the spinal cord leading to classic paralysis.

History of polio

Michael Underwood from Britain first reported this debilitating paralysis of lower limbs in children in 1789.

The early 19th century saw the initial outbreaks in Europe followed by similar outbreaks in the United States a few years later.

Outbreaks and epidemics of polio were common in the northern hemisphere for the next century every summer and fall.

The disease additionally became more severe with more deaths from polio. In 1952 there were over 20,000 paralytic cases signifying peak rise in the numbers.

Transmission electron micrograph (TEM) of poliovirus type 1. Virions are 20-30nm in diameter, and have icosahedral symmetry. Image Credit: CDC

Sir Gus Nossal is a world-renowned scientist, Member of the Order of Australia, and one of Australia's Living National Treasures. In the 1950s he experienced first-hand the fear and panic that polio's spread creates. Decades later, as one of the world's leading immunologists, he also knows the devastating impact this disease has, and how remarkable it has been to achieve a 99% reduction of cases, and bring eradication within reach.

Introduction of polio vaccines

The numbers of deaths and paralytic cases from polio, however, declined following introduction of effective vaccines. United States for example has reported its last case of wild-virus polio in 1979.

Polio in developing countries

Outbreaks still occur in the developing countries, usually in groups of people who have not been vaccinated.

There are now only four countries in which the condition remains a serious health problem. These are:

  • Nigeria
  • India
  • Afghanistan
  • Pakistan.

It is hoped that with vaccination worldwide the disease may be eradicated worldwide in the next decade. (1-5)

This 1989 photograph depicted a polio patient’s lower limb leg splints lying on a tiled floor, which when worn by a polio victim who’s lower limbs had become paralyzed, would help the person maintain an upright position. Image Credit: CDC

Cause of polio

Polio is caused by a virus that can affect the nerves of the spinal cord leading to partial or full paralysis.

The virus spreads by person to person contact, contact with infected mucus from mouth or nose and contact with water contaminated with infected faeces.

The virus enters the mouth and nose and starts to multiply in the throat and intestines. From there it reaches the blood vessels and lymphatic channels. On average an infection takes 7 to 14 days to manifest. (1-5)

Who is at risk of polio?

Those at risk of getting polio include children without vaccine who are exposed to the virus and unvaccinated or unexposed travellers to an area where there is a polio outbreak.

Pregnant women, children and the elderly are more at risk.

Polio infection can manifest as subclinical infections with no paralysis or symptoms; nonparalytic, and paralytic forms of polio without and with paralysis respectively.

About 95% of infections are subclinical infections, which may have no symptoms. Of the rest 4-8% have the non-paralytic variety and 1% develops paralysis. (1-5)

Treatment of polio

The goal of treatment of polio is to reduce and control the symptoms while the infection runs its course. In severe paralysis - that may affect the respiratory muscles as well leading to difficulty in breathing - life saving measures are needed.

Symptoms are treated based on their severity. There is no specific treatment against polio.

If the spinal cord and brain are spared by the infection, which is the case more than 90% of the time, complete recovery is very likely.

However, if the spinal cord or brain is affected there is a risk of respiratory paralysis and death. Infection that is located high in the spinal cord or in the brain increases the risk of breathing problems and difficulties.

Many patients with lesions in the lower spinal cord however may go on to develop permanent paralysis or disability of the lower limbs. (1-5)

Prevention of polio

Polio cannot be cured once the disease begins. Thus treatment focuses more on prevention.

Polio vaccine effectively prevents poliomyelitis in most people with over 90% effectiveness in most populations.

There are two types of vaccine that can prevent polio. This includes the inactivated polio vaccine (IPV given as injection) and oral polio vaccine (OPV – given as drops). (1-5)

Causes of Polio

Poliomyelitis is a viral illness. It leads to infection of the nerves and sometimes the spinal cord and the brain leading to partial or complete paralysis.

Poliomyelitis is a disease caused by infection with the poliovirus. This virus spreads via person to person contact, via contact with infected mucus from the nose or mouth of the infected child and on contact with infected faeces usually through contaminated water. (1-4)

How does the virus cause polio?

The infection occurs through the gastro-intestinal route. On contact the virus enters through the mouth or nose and goes on to multiply in the throat and intestines.

From there it is taken up by blood vessels and lymphatic channels.

The time from being infected with the virus to developing symptoms (termed incubation period) ranges from 5 - 35 days (average 7 - 14 days).

In about 95% cases the infection is mild and harmless. However in 1% or less number of individuals there may be paralysis of limbs or other muscles, brain affliction or meningitis and encephalitis.

This happens when the virus invades the nerves of the spinal cord (especially a part of the spinal cord called the anterior horn) and lower part of the brain called the brain stem.

The brain stem deals with controlling the respiration. Damage to this area may lead to paralysis of muscles of respiration and even death. Damage to the spinal cord may lead to permanent muscle weakness and disability. (1-4)

Who is at risk of polio?

Children who have never been vaccinated are at a higher risk of getting polio.

Additionally, children, pregnant women and elderly who have never been exposed to the infection and never been vaccinated are at a higher risk of getting the infection if they visit an area where there is a polio outbreak. The disease is more common in the summer and fall. (1-4)

Types of polio

Types of polio virus include (2) –

  • Wild virus – This is the naturally present polio virus. This is the culprit virus that causes paralytic polio in countries where the infection is widespread. It has three sub varieties. These are termed P1, P2 and P3.
  • Vaccine-induced paralytic polio (VAPP) – The polio vaccine is made by live attenuated viruses. In other words weakened but living polio viruses are used in the vaccine.

When administered the body learns to recognise the virus and prepares its immune defences against the real active virus when it comes in contact with the individual.

Rarely the vaccine virus in the oral polio vaccine (OPV) can cause paralysis - either in the vaccinated child, or in a close contact. This occurs in about 1 in 2.5 million doses of the vaccine.

  • Vaccine-derived polioviruses (VDPVs) – Very rarely a strain of virus in the OPV may genetically change to become a more virulent form and cause paralysis. This is called vaccine-derived polioviruses (VDPVs).

The polio virus

The polio virus belongs to the enterovirus subgroup within family Picornaviridae. Enteroviruses are those that are transient inhabitants of the gastrointestinal tract. They can sustain at acid pH.

These are small viruses that have RNA as their genetic material. The polio virus may be destroyed by heat, chemicals like formaldehyde and chlorine and by ultraviolet light. (3)

Symptoms of Polio

Poliomyelitis may manifest with a range of symptoms. These may vary according to severity.

For example, a large number of infected individuals have no apparent signs of infection and are thus termed asymptomatic. These patients however may transmit the virus by shedding it in their stools.

The symptoms of polio may be outlined as subclinical infection, non paralytic polio and so forth. (1-5)

Subclinical infection

This is seen in 95% of individuals infected with polio. In places where outbreaks are common, children with this type of infection are called the “reservoirs” of polio since they inadvertently shed the virus in their stools that gets transmitted to other exposed individuals.

There is a general feeling of illness or malaise, red and sore throat, fever (mild), headache and sometimes vomiting. The symptoms may last for less than 72 hours.

Non-paralytic polio

Non paralytic polio may last for a week or two. It is characterized by:

  • back pain
  • muscle stiffness
  • headache
  • fatigue
  • irritability
  • diarrhea
  • pain over the calf muscles
  • mild to moderate fever
  • muscle spasm and pain
  • neck pain and stiffness
  • pain in front of the neck or in the back, arms, abdomen and legs
  • skin rashes
  • nausea with vomiting

Paralytic polio

In less than 1% of polio infections the virus may invade the nerves of the anterior horn of the spinal cord. It specifically affects the nerves that control motor movements.

If the spinal cord is affected closer to the brain or if the lower part of the brain called the brain stem is affected there may be severe paralysis of the respiratory muscles making it difficult to breathe. This may be life threatening.

In the lower parts of the spinal cord the infection may lead to permanent muscle weakness of the lower limbs and paralysis and disability. Thus the level of spinal cord that is affected determines the outcome of the illness.

It is called spinal (commonest of paralytic polios), bulbar (seen in 2% of paralytic cases) or spinobulbar or bulbospinal (seen in 19% of paralytic cases).

Spinal paralysis affects the spine and leads to paralyzed legs. This is seen in 80% of the paralytic cases. The paralysis of the legs may be patchy and non-uniform. In bulbar polio the brain is affected.

Paralytic polio begins with a fever for 5 to 7 days before any other symptom.

There may be:

  • abnormal sensation in the paralyzed area
  • bloating of the abdomen
  • constipation
  • difficulty in urinating
  • difficulty breathing
  • drooling
  • headache and irritability
  • muscle pain and stiffness in the back, neck and legs
  • weakness over one side that comes in quickly and worsens into paralysis
  • simple touch may be painful
  • there may be difficulty in swallowing

Post-polio syndrome

After resolution of the symptoms of polio the patient may develop post-polio syndrome (PPS). This may appear 30 to 40 years after the initial infection.

There is severe muscle weakness and paralysis of the previously unaffected muscles. It is rarely fatal but has a slow and unpredictable course. PPS is not infective.

Diagnosis of Polio

Polio is caused by a viral infection. In most cases (95% infections) there are no clinical symptoms and these infections do not need treatment.

However, these patients continue to shed the virus in their stools and act as reservoirs of infection.

Those with non-paralytic and paralytic forms of polio manifest the disease clinically.

Diagnosis of polio involves medical history, physical examination and so forth. (1-5)

Medical history

Medical history of the patient includes enquiry about exposure to a case of polio. This includes travelling to an area where polio in endemic, direct contact with nasal or mucus secretions of an individual with polio infection.

History or polio vaccination is also important. Inactivated injectable polio vaccine or IPV for example has an effectiveness of around 90% protection from the infection. Individuals who are vaccinated are usually protected from the infection.

Medical history also includes feeling of illness and fever.

Physical examination

This involves a complete check up of the systems. The respiratory muscles are examined for function as polio affecting spinal cord and brain stem may affect respiratory muscles.

Muscle reflexes are tested. Abnormal reflexes are detected. There may be a stiff neck and stiff muscles of the back. There may be difficulty in bending the neck and difficulty in lifting the head or legs when lying flat on the back.

Acute flaccid paralysis

Acute flaccid paralysis (AFP) is a common clinical manifestation of poliomyelitis. AFP is defined as the sudden onset of flaccid paralysis in one or more limbs.

AFP is also caused by Guillain-Barré syndrome and transverse myelitis. AFP is monitored closely worldwide to detect stray cases of polio due to wild virus subtypes.

Laboratory diagnosis

Laboratory diagnosis includes routine blood tests. There may be raised white blood cells.

Cerebrospinal fluid examination

The Cerebrospinal fluid bathes the spinal cord and the brain. This CSF is tested using a lumbar puncture. Lumbar puncture involves insertion of a long thin needle between the vertebrae. This draws out a small amount of CSF that is sent to the laboratory for evaluation.

Routine CSF examination includes assessment of cells (white blood cells, blood etc.) and levels of sugar and other chemicals in the CSF. Typically there are 10 to 200 cells/mm3 and there may be a mildly elevated protein content in CSF from 40 to 50 mg/100 ml.

Throat washing

Throat washing is taken and assessed for the virus. The washings are incubated at a favourable atmosphere in a culture media.

If the culture is positive for the virus it may be detected under microscope. Stool samples are also examined for polio virus. Isolation of virus from the cerebrospinal fluid (CSF) is diagnostic but is rarely possible.

Blood tests

Blood is tested for antibodies for polio virus. Antibodies are molecules that are produced by the body against an invading virus or bacteria.

When a person is infected with polio virus, special tests can detect the levels of polio virus specific antibodies and confirm the diagnosis.

Fingerprinting the polio virus

Once the polio virus is isolated it is tested by a special test called oligonucleotide mapping (fingerprinting) or genomic sequencing. This is essentially looking at the genetic sequence of the virus to detect if the origin of the virus is “wild type” or “vaccine like”.

Wild type virus naturally occurs in the environment and may occur as 3 subtypes – P1, P2 and P3. Vaccine like virus is derived after a spontaneous mutation of the genes of the virus in the polio vaccine.