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Polio

Overview

Poliomyelitis, usually referred to as Polio, is a viral infection caused by Poliovirus. Poliovirus is a member of the Picornaviradae family and of the Enterovirus genus. The virus is highly infectious and can invade the nervous system to cause paralysis in a matter of hours. It most commonly affects children under 5 years old. 1 in 200 cases result in irreversible paralysis, usually in the legs. 5-10% of paralysed individuals have their breathing muscles immobilised, leading to fatality. Since 1988, the number of reported cases has reduced by 99% from 350,000 to 359 in 2014. 125 countries were endemic in 1988, whilst now just Afghanistan and Pakistan remain Polio-endemic. The reduction in cases is due to the global effort of building effective surveillance and immunisation programmes. The UK has not experienced an endemic case of poliomyelitis since 1984.

 

Signs and symptoms

The majority of individuals infected with the virus will remain asymptomatic whilst 1 in 4 experience mild symptoms of:

  • Fever

  • Fatigue

  • Headache

  • Vomiting

  • Sore throat

 

More severe cases present with:

  • Stiffness of the neck

  • Pain in the limbs

  • Loss of reflexes

  • Severe myalgia

  • Weakness

  • Loose and floppy limbs, often worse on one side of                                                                                                                 the body

  • Meningitis

 

Complications can develop years later in some individuals, known as post-polio syndrome which has disabling signs and symptoms such as:

  • Progressive muscle/joint weakness and pain

  • General fatigue and exhaustion after minimal activity

  • Muscle atrophy

  • Breathing or swallowing problems

  • Sleep-related breathing disorders - sleep apnoea

  • Decreased tolerance of cold temperatures

  • Cognitive problems - concentration and memory difficulties

  • Depression

  • Mood swings

 

Causes

The poliovirus resides only in humans. It is spread primarily through the faecal-oral route, especially in areas with poor sanitation and limited/no access to clean water. Poliovirus can be transmitted through contaminated food/water or through direct contact with an infected individual. The virus can also be spread through airborne droplets when an infected person sneezes or coughs. Polio is extremely contagious and anyone living with a recently infected individual is extremely likely to become infected. The virus is contagious 1 week before symptoms develop and remains infectious in the faeces for several weeks after symptoms have ended. The virus enters through the gastrointestinal tract where it replicates in the gut and surrounding lymphoid tissue. Patients are no longer asymptomatic when the virus reaches reticuloendothelial tissue via the bloodstream. At this point symptoms of minor illness present (fever, sore throat, headache etc.).

 

Paralytic poliomyelitis occurs in <1% of reported cases, where the virus enters the central nervous system and replicates in motor neurons in the spinal cord, medulla and pons. Motor neurons become destroyed as a result and the related skeletal muscles lose function due to acute flaccid paralysis, due to lack of nervous enervation.

 

The most severe cases show bulbar polio, where the virus attacks the motor neurons of the brain stem. This reduces breathing capacity and causes swallowing and speaking difficulties. Fatality results in the absence of respiratory support.

 

Risk factors / at risk groups

  • Travel to an endemic area

  • Living with/caring for an infected individual

  • Children aged under 5 years old.

  • Pregnant women

  • Individuals with a compromised immune system

  • Individuals who have had a tonsillectomy

 

Diagnosis / microbiology testing

Usually diagnosed by symptoms and clinical assessment. To confirm diagnosis, a sample of

throat secretions, stools or cerebrospinal fluid is checked for poliovirus presence.

 

Treatment

There is no recommended antiviral treatment for poliomyelitis. Treatment focuses on preventing complications, reducing recovery time and increasing patient comfort. Supportive treatment includes:

  • Bed rest to reduce paralysis extension

  • Analgesics

  • Ventilators and breathing support once vital capacity falls to >50%

  • Tracheal intubation required in severe bulbar paralysis

  • Physical therapy to prevent deformity and loss of muscle function once paralysis progression has ceased

  • Splints/braces to support weak limbs/joints

Intramuscular injections must be avoided in poliomyelitis.

 

Vaccine / preventative measures

The inactivated poliovirus vaccine (IPV) was introduced in 1956. It now contains all 3 serotypes. Neutralising antibodies are present in 100% of vaccinated individuals after the third dose. It can be administered alone or in combination with other vaccines for diphtheria, tetanus, pertussis, hepatitis B and

haemophilus influenza. The vaccine is given in 5 doses and the

NHS recommends administration to occur when the individual is

aged 2 months, 3 months, 4 months, 3 years and 4 months and

finally between 13-18 years old.

 

Alternatively, an oral vaccine (OPV) was developed in 1963. OPV

consists of live attenuated poliovirus strains of all 3 serotypes. OPV

promotes antibody formation in the gut and boosts community

immunity. 1 dose in every 2.6 million results in vaccine-virus related

disease. However, it remains the vaccine of choice in developing

areas due to its lower cost and simpler administration.

 

Preventative measures include:

  • Avoiding endemic areas

  • Avoiding infected people

  • Washing hands often

  • Avoid touching eyes, nose or mouth unless hands are clean

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