Poliomyelitis

This disease is notifiable in the UK under the Public Health (Infectious Diseases) Regulations 1988.

Infection with the poliovirus, an enterovirus (picornaviridae). Also known as infantile paralysis, it has been around since the time of ancient Egypt. When infected early, maternal antibodies confine the infection to the gut until the baby's immune response is able to eliminate it. There are 3 different types of poliovirus

• Abortive (flu-like illness)
• Non-paralytic (aseptic meningitis)
• Paralytic (with variable severity and recovery).

• Virtually eradicated from the Western world¹ but still endemic in India, Pakistan, countries of West and Central Africa and Middle East.
• Spreads by contamination of food or drink by faeces. May result from exposure (via faecal-oral spread) to live attenuated poliovirus used in oral polio vaccination.² Incidence from oral polio vaccine has been estimated to be about one in 2-3 million vaccine doses.
• Epidemics usually occur when there is overcrowding, insufficient immunization, and poor sanitary conditions.
• Only about 5-10% of people exposed to human poliovirus develop symptoms.
• Risk factors for developing the paralytic form include elderly if not immunised, recent tonsillectomy, intramuscular injections, pregnancy, strenuous exercise and immune deficiency.

• In 99% cases: minor illness (abortive poliomyelitis) with fever, malaise, headache, vomiting, diarrhoea, constipation and sore throat.
• Non-paralytic poliomyelitis: in 0.9% of cases in addition to above, aseptic meningitis with neck and back stiffness. Recovery usually occurs after 10 days.
• Paralytic poliomyelitis (0.1% of infections): 5-10 days after respiratory infection, an asymmetrical flaccid paralysis caused by motor neurone destruction (major illness). Features include intense myalgia, hyperaesthesia as well as sensory loss.
• Variations include predominantly spinal, predominantly bulbar, mixed, predominantly dysautonomia and encephalitic (with changes in mental state and seizures).
  • Weakness most often affects the lumbar region and therefore lower limbs.
  • Bulbar weakness occurs in 10-20% of cases and presents with double vision, dysphagia, dysphonia, facial weakness and difficulty in chewing, swallowing and expelling of saliva with regurgitation of fluids through the nose. Bulbar form may cause lethargy or coma due to hypoxia caused by hypoventilation and progress to respiratory paralysis.

• Bacterial or other viral meningitis; encephalitis
• Guillain-Barre syndrome
• Transverse myelitis
• Diphtheria.

• CSF: raised leucocytes, predominantly lymphocytes, after first 24 hours
• Poliovirus isolation: polymerase chain reaction from CSF, saliva, or stool
• Serology: rise in IgM poliovirus titre
• MRI of the spinal cord: preferential involvement of the ventral horn of the spinal cord
• Electromyography and nerve conduction studies: anterior horn cell involvement and no evidence of demyelination or sensory nerve dysfunction.

Management involves variable degrees of supportive therapy.

• Strict bed rest in first days of illness reduces rates of paralysis. However measures to avoid bed sores, e.g. by using a firm mattress, frequently changing position, are essential
• Aspirin or paracetamol for fever and analgesia
• Measures to combat constipation and faecal impaction, e.g. fluids, high fibre diet, laxatives
• Treatment for urinary retention - may require catheterization
• Respiratory support: may require ventilation, which should be started before hypoxia develops. Tracheostomy may also be required
• Rehabilitation may require physiotherapy, occupational therapy and orthopaedic surgery (e.g. spinal fusion, orthoses).

• In children under 5 years old, the commonest outcome is paralysis of one leg. In children aged 5-15 years most often develop weakness of one leg or paraplegia.
• In adults, quadriplegia is more common, often with urinary bladder symptoms and respiratory muscle dysfunction. 90% survivors have residual paralysis but some muscle function may return slowly.
• Other potential complications include pneumonia (including aspiration pneumonia), myocarditis, paralytic ileus and bowel perforation, and urinary tract infection.
• Disablity caused by paralytic poliomyelitis may lead to severe psychological (e.g. depression) and social difficulties.

• Recovery from paralytic poliomyelitis is variable over 2-6 months.
• Mortality is 2-5% in children and 15-30% in adults. Most deaths occur within the first 2 weeks. Bulbar poliomyelitis may have mortality of up to 50%.
• Up to 30% of patients with paralytic poliomyelitis who appear to recover fully go on to develop post-polio syndrome 20-40 years after the acute illness.

Immunisation is routinely part of the child immunisation programme.

• There are two types of vaccine:
  • Inactivated: Salk vaccine given by injection.
  • Live attenuated: Sabin vaccine given orally. Parallels natural infection and is easy to administer and more cost effective. However, may be problems in tropics with maintaining correct temperature during storage also, risk of vaccine-associated poliomyelitis.
• In 2004 the UK switched from live attenuated oral polio vaccine (OPV) to inactivated polio vaccine (IPV) injections. IPV contains inactivated strains of three types of human polioviruses (1, 2 and 3). OPV (Sabin) and IPV (Salk) both give good individual immunity but OPV can rarely revert back to a virulent strain causing vaccine associated paralytic polio (VAPP).
• Polio vaccine should be given to people travelling into endemic areas at least 2 weeks before departure if they have not been vaccinated within the last 10 years.