Poliomyelitis (polio) is caused by infection with the poliovirus, an enterovirus. The virus may invade lymphatic tissue and spread into the bloodstream. It can be neurotropic, destroying motor neurons, particularly in the anterior horn of the spinal cord and brain stem. This causes flaccid paralysis which may be spinal or bulbar.
Poliomyelitis causes a spectrum of illness from asymptomatic (most infections) to a meningitic or paralytic acute illness; the paralytic form can cause permanent muscle weakness. Acute polio infection is now rare in most countries following immunisation programmes. Polio survivors may have residual disability or post-polio syndrome.
Aetiology, epidemiology and transmission
'Wild' polio infection
- The naturally occurring poliovirus is known as 'wild virus'. There are three subtypes of poliovirus; type 1 was the most common before vaccination was introduced. Wild type 2 virus has not caused a case since 1999 and type 3 since 2012.
- 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.
- Since its launch in 1988, the World Health Organization's Global Polio Eradication Initiative has reduced worldwide polio incidence by over 99%.
- By 2003, the early programmes had reduced the number of countries with serious endemic infection to four: India, Pakistan, Afghanistan and Nigeria.
- Subsequent years have seen only limited progress in preventing the last 1% of cases, particularly with continued endemicity in Pakistan and Afghanistan. There has been success in India and Nigeria.
- There have also been recent cases elsewhere - eg, Syria.
- Risk factors for developing the paralytic form of infection (rather than mild illness) include physical activity and intramuscular injections.
- One review found that the bulbar form of acute polio was more common in children who had undergone tonsillectomy and adenoidectomy.
Polio associated with vaccines
Vaccine-associated 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, 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 (VDPVs): also rarely, a strain of poliovirus in OPV may genetically change so that it can both cause paralysis and circulate among a population.
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 0.5%. Clinical features are:
- Initially, a flu-like illness, then symptoms subside for a few days.
- Symptoms then recur with myalgia, severe muscle spasms 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.
- Bacterial or other viral meningitis; encephalitis.
- Other causes of acute flaccid paralysis - eg:
- 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.
Notification and contacts
- For any suspected case of polio infection, report it immediately to a consultant in communicable diseases.
- Household contacts require immediate polio vaccination. Other people in the neighbourhood may also require vaccination.
- A supply of the appropriate vaccine will be issued on Public Health England advice.
Acute paralytic polio
- Strict bed rest to prevent extension of the paralysis.
- Supportive care - eg:
- Prevent problems related to immobility - eg, pressure sores, constipation.
- A urinary catheter may be needed.
- Acute respiratory failure can develop rapidly; the patient may need respiratory support and/or tracheostomy.
Prevent deformity by stretching exercises and splinting of affected limbs.
- Intensive physiotherapy.
- Orthoses and splints if needed.
- Occupational therapy.
Complications of paralytic polio
- 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
- Limbs which are less used or are non-weight-bearing 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.
- 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 overuse of muscles.
- Detecting and treating problems early - eg, respiratory problems.
The milder spectrum of poliovirus infection (asymptomatic or flu-like illness only) carries no specific complications.
With paralytic polio, muscle function may return gradually. However 5-10% of people with paralytic polio will die when their breathing muscles become affected. There is some residual paralysis in the majority of survivors. Mortality is higher in adults than in children and with bulbar poliomyelitis.
See also the separate Immunisation Schedule (UK) article.
- 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 VAPP (see above).
- Because OPV can rarely cause paralysis and generate revertant polio strains, inactivated polio vaccine (IPV) will have to replace OPV after eradication of wild polio virus is certified in order to sustain eradication of all polioviruses. However, uncertainties remain, related to IPV's ability to induce intestinal immunity in populations where faecal-oral transmission is predominant.
- In 2004 the UK switched from live attenuated OPV to IPV injections. OPV is no longer available for routine use.
- The polio vaccine is now only given as part of combined products:
- Diphtheria/tetanus/acellular pertussis/inactivated polio vaccine/Haemophilus influenzae type b (DTaP/IPV/Hib)
- Diphtheria/tetanus/acellular pertussis/inactivated polio vaccine (DTaP/IPV, or dTaP/IPV)
- Tetanus/diphtheria/inactivated polio vaccine (Td/IPV).
- These vaccines are inactivated, do not contain live organisms and cannot cause the diseases against which they protect. IPV can therefore be given safely to people with immunosuppression (including those with HIV) and to pregnant and breast-feeding women.
- Td/IPV vaccine should be used where protection is required against tetanus, diphtheria or polio in order to provide comprehensive, long-term protection against all three diseases.
- Vaccines should be stored in the original packaging at +2°C to +8°C and protected from light.
- The vaccines should not be given to those who have had:
- A confirmed anaphylactic reaction to a previous dose of IPV-containing vaccine; or
- A confirmed anaphylactic reaction to neomycin, streptomycin or polymyxin B (which may be present in trace amounts).
|Children||Adults (who have not been immunised as a child)|
|Primary Course||Three doses of vaccine - as DTaP/IPV(polio)/Hib at 2, 3 and 4 months of age.||Three doses of vaccine - as Td/IPV(polio), each one month apart.|
|Fourth dose||Three years after the primary course - as part of the DTaP/IPV(polio) pre-school booster at 3 years and 4 months to 5 years.||Five years after the primary course - as Td/IPV(polio).|
|Fifth dose||Aged 13-18 years - the school leaver booster - as Td/IPV(polio).||10 years after the fourth dose - as Td/IPV(polio).|
If the primary course is interrupted it should be resumed but not repeated, allowing an interval of one month between the remaining doses. Those who commenced vaccination with OPV can complete the course with IPV-containing vaccines.
Those born before 1962 may not have been immunised or may have received a low-potency polio vaccine.
All travellers to epidemic or endemic areas should ensure that they are fully immunised according to the UK schedule (see above). Additional doses of vaccines may be required according to the destination and the nature of travel intended.
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