Aetiology, epidemiology and transmission^[1]

'Wild' polio infection

• The naturally occurring polio virus is known as 'wild virus'. There are 3 subtypes of poliovirus; type 1 was commonest before vaccination was introduced.
• The infection is transmitted by the faeco-oral route:
  • Infection is oral and the virus has high infectivity.
  • The virus multiplies in the oropharynx for 1-3 weeks. It is then excreted in saliva for a few days and in faeces for 2-3 weeks.
  • Most infections (95%) are mild, either asymptomatic or with a mild flu-like illness.
• Polio has been eradicated from many countries, but is still endemic in India, Nigeria, Pakistan and Afghanistan. There have also been recent cases elsewhere, eg Angola, Chad and Niger.^[2]
• Risk factors for developing the paralytic form of infection (rather than mild illness) include physical activity and intramuscular injections. The bulbar form of acute polio was more common in children who had undergone tonsillectomy and adenoidectomy.^[1]

Polio associated with vaccines^[3]

• Vaccine-induced paralytic polio (VAPP):
  • Rarely, the live attenuated vaccine virus in oral polio vaccine (OPV) can cause paralysis - either in the vaccinated child, or in a close contact. Immune deficiency of the recipient may contribute.
  • This occurs in about 1 in 2.5 million doses of the vaccine.
  • It may affect either the vaccinated person or their contacts,^[4] because the vaccinated person excretes the virus.
  • Many countries, including the UK, are now using the inactive (injected) vaccine for this reason.
• Vaccine-derived polioviruses (VDPV):
  • Also rarely, a strain of poliovirus in OPV may genetically change so that it can both cause paralysis and circulate among a population.

Pathophysiology^[5]

The virus may invade lymphatic tissue and spread into the bloodstream. It can be neurotropic, destroying motor neurones particularly in the anterior horn of the spinal cord and brainstem. This causes flaccid paralysis which may be spinal or bulbar.

Presentation^[1][6][7]

With acute poliovirus infection, there are various clinical scenarios :

• No symptoms, or flu-like illness ('abortive infection') - 95%.
• Non-paralytic polio (flu-like symptoms plus aseptic meningitis) - about 4%.
• Paralytic (with variable severity and recovery) - about 1%. Clinical features are:
  • Initially, a flu-like illness, then symptoms subside for a few days.
  • Symptoms then recur with myalgia. severe muscle spams and meningism for a few days.
  • Next there is asymmetrical, flaccid motor paralysis, predominantly lower limb. This maximises at 48 hours.
  • There is also a bulbar form of paralysis (about 10-25% of paralytic cases). This may cause autonomic features, eg hyper/hypotension, respiratory failure, and bulbar symptoms, such as dysphagia and dysphonia.
• Rarely, acute encephalitis can occur from poliovirus.

Differential diagnosis^[1]

• Bacterial or other viral meningitis; encephalitis
• Other causes of acute flaccid paralysis, e.g:
  • Various infections
  • Guillain-Barré syndrome
  • Spinal cord lesions
  • Neuropathies
  • Myasthenia gravis
  • Myopathy or myositis.

A full list is given elsewhere.^[1]

Investigations^[5]

• Serology: take acute and convalescent samples. A positive IgM or a four-fold increase in IgG is diagnostic.
• The virus can be detected by polymerase chain reaction using samples from throat, stool or CSF.

Management^[1]

Notification and contacts:

• For any suspected case of polio infection, report immediately to a consultant in communicable diseases.
• Household contacts require immediate polio vaccination (click here for details in separate Polio Vaccination article). Other people in the neighbourhood may also require vaccination.
• A supply of the appropriate vaccine will be issued on Health Protection Agency advice.

Acute paralytic polio:

• Strict bed rest to prevent extension of the paralysis
• Supportive care, e.g:
  • Prevent problems related to immobility, eg pressure sores, constipation
  • Analgesia
  • May need urinary catheter
  • Acute respiratory failure can develop rapidly; may need respiratory support and/or tracheostomy

Recovery:

• Prevent deformity by stretching exercises and splinting of affected limbs

Rehabilitation:

• Intensive physiotherapy
• Orthoses and splints if needed
• Occupational therapy

Complications of paralytic polio^[1][7]

Early complications

• Paralysis, often of one leg or paraplegia. Quadriplegia is more common in adults, possibly with bladder and respiratory muscle dysfunction.
• Other potential complications include pneumonia (including aspiration pneumonia) and urinary tract infection.

Late complications and their prevention

Osteoporosis and osteomalacia:

• Limbs which are less used or are non-weightbearing are vulnerable to osteopenia.
• Patients spending less time outdoors are at risk of vitamin D deficiency and osteomalacia, which can exacerbate bone and joint problems.

Post-polio syndrome (see separate article):

• This can occur years (or many years) after acute polio.
• It comprises symptoms such as functional deterioration, fatigue and respiratory problems.
• Prevention or amelioration of post-polio syndrome may be possible to some extent by:
  • Maximising support for the polio disability, eg ensuring aids and orthoses are correctly fitting.
  • Avoiding over-use of muscles.
  • Detecting and treating problems early, eg respiratory problems.

Prognosis^[5][7]

• The milder spectrum of poliovirus infection (asymptomatic or flu-like illness only) carries no specific complications.
• With paralytic polio:
  • Muscle function can return gradually, but there is some residual paralysis in 90% of polio survivors.
  • Mortality is 2-5% in children and 15-30% in adults. Most deaths occur within the first 2 weeks. Bulbar poliomyelitis may have a mortality of up to 60%.

Prevention^[8]

Immunisation - see separate article on Polio Vaccination above.

• There are two types of vaccine:
  • Inactivated: the Salk vaccine given by injection.
  • Live attenuated: the Sabin vaccine given orally. This parallels natural infection and has some advantages. However, with OPV there is a small risk of vaccine-associated paralytic polio (see above).
• In 2004 the UK switched from live attenuated OPV to inactivated polio vaccine (IPV) injections.

Polio vaccination in the UK^[8]:

• This is part of the childhood immunisation programme.
• Immunisation should also be given to:
  • Those who do not have a reliable history of completed polio vaccination of a type suitable for the UK environment (further details in the 'Green Book'^[8]).
  • Those born in the UK before 1962, who may not have had full immunisation.
  • Polio vaccination may be required for those travelling to endemic areas (depending on destination).