Poliomyelitis (polio) is a highly contagious disease, but in the majority of cases it causes no symptoms.
Since the implementation of polio vaccines the number of cases has greatly reduced, and many countries are now thought to have eliminated the poliovirus. Infection is possible in certain countries of Asia and Africa if immunization coverage is suboptimal.
Rapidly developing flaccid paralysis is asymmetrical. Sensation is preserved in the paralysed limbs.
Post-polio syndrome (e.g. fatigue, muscle weakness, myalgia and arthralgia) is a condition that affects patients several years after recovery from an initial acute attack. The treatment of these late effects is symptomatic (analgesia, exercises, rest, weight control, assistive devices).
Transmission
The poliovirus belongs to the enterovirus genus of the picornavirus family.
There are 3 serotypes of wild poliovirus. Wild poliovirus type 2 has been eradicated from the world already in 2015 and wild poliovirus type 3 in 2019. Consequently, the only wild poliovirus that causes the disease is type 1, which still occurs in Pakistan and Afghanistan. Disease caused by vaccine derived polio viruses (VDPV) has been detected in several other countries.
Polio is a highly contagious disease.
Human-to-human transmission occurs via the respiratory route or through contaminated food or drink.
The incubation period is 7-18 days.
Clinical picture
Polio causes no symptoms in over 90% of cases.
Fewer than 10% of infected individuals will develop signs of an infection, e.g. fever, malaise and sore throat.
After a few days, paralytic symptoms appear; these occur in less than 1% of non-vaccinated infected patients.
The rapidly developing flaccid paralysis is typically asymmetrical. The poliovirus only damages motor neurones so there is no sensory loss, but sensory disturbances may occur.
Respiratory distress may be caused by muscle weakness as well as by damage to the respiratory centre.
In a small proportion of patients with paralytic disease, an infection of the medulla oblongata will lead to bulbar symptoms, including difficulty in speaking and swallowing as well as paralysis of the eye muscles.
Recovery begins a few weeks after the onset of symptoms, and in about half of patients the recovery will be almost or totally complete.
Diagnosis
The confirmation of a virological diagnosis requires two stool samples collected on two consecutive days during the first two weeks after the onset of paralysis. The virus is excreted even longer, but after this time the proportion of culture-negative samples increases.
Additional samples may include a throat swab for a viral culture as well as serum and CSF fluid samples for antibody analysis at the start of the disease and two weeks later.
Samples must be sent to the appropriate local laboratories.
Polio is a notifiable disease, and local government officials must be informed of all cases confirmed by laboratory testing.
Differential diagnosis
Coxsackie, ECHO virus and other enteroviruses may cause mild symptoms which resemble polio.
There are two types of polio vaccine: inactivated polio vaccine (IPV) which is given by injection and live oral polio vaccine (OPV).
A decision is made nationally as to which vaccine to use. IPV is currently used routinely in many countries.
Immunization schedules vary slightly from country to country. IPV is usually a part of the combination vaccine given routinely to children.
In the national immunization programme applied in Finland, the IPV vaccine is included in the multicomponent combination vaccine given at the ages 3 months, 5 months, 12 months and 4 years.
If the vaccinations are started at an older age, three doses of IPV vaccine given at 0, 2 and 6 months provide sufficient protection.
Additional doses of vaccine may be required by travellers to endemic areas. Travellers should ensure they are fully immunized in accordance with the current immunization guidelines.
When travelling for longer than 4 weeks in a country where polio still occurs, has occurred in recent years or where there is an increased risk of the disease spreading from country to country, a booster vaccine should be given if more than 12 months have passed since the previous vaccination. If the time spent in the country is less than 4 weeks, no booster vaccination is required.
A person who has had polio will only have immunity against one serotype of the virus and will therefore still need to be vaccinated.
Post-polio syndrome
Post-polio syndrome (PPS) affects some patients who have previously contracted polio. PPS is characterised by the emergence of new symptoms. The most common symptoms include fatigue, muscle weakness, myalgia and arthralgia
The symptoms usually develop gradually, but in some cases they may emerge suddenly, e.g. during a period of bed rest following an injury or surgery.
Late effects may also develop in some patients who experienced no paralysis during the acute disease phase.
The exact cause of PPS is unknown, but the most common theory involves the combined effect of overuse and premature ageing of motor neurones.
Diagnostic criteria
History of paralytic polio with evidence of motor neurone loss
History of the acute paralytic illness
Weakness and atrophy of muscles noted on neurological examination
Signs of denervation on electroneuromyography (ENMG)
Partial or complete recovery after the acute disease, followed by a neurologically and functionally stable interval (usually 15 years or more)
Gradual or sudden onset of progressive and persistent new muscle weakness or abnormal muscle fatigability (decreased endurance). Further symptoms may include increased fatigue, muscle atrophy, myalgia and arthralgia. Less commonly, problems with breathing or swallowing may occur.
Symptoms have persisted for at least a year.
Other neurological, medical and orthopaedic problems as causes of symptoms have been excluded.
Treatment and rehabilitation
So far no specific medication exists to treat the late effects of polio Treatment for Postpolio Syndrome; pain management should follow the usual guidelines. The most important treatment forms include exercises to maintain mobility and functional capacity, a sufficient amount of rest, weight control and the introduction of suitable assistive devices.
Improvement and/or maintenance of mobility
An individual self-care plan should be drawn up, based on an assessment by a physiotherapist
Exercise should be regular and varied; it is important to strike a balance between exercise and rest
Hydrotherapy
Breathing exercises (e.g. using a “blow bottle” device)
If needed, a rehabilitation plan should be drawn up (e.g. outpatient physiotherapy, multidisciplinary individual rehabilitation, rehabilitation and adjustment training courses).
Developing the patient's mental resources
Assessing the need for assistive devices, testing them and providing guidance
Consideration of whether the patient's home needs to be adapted
Assessing the feasibility of, and the patient's need for, vocational rehabilitation
Mapping out the social security assistance available, and the completing of applications and issuing of relevant statements
Management of specific problems
Assessment of respiratory function (spirometry, sleep apnoea investigations, a referral to a specialist in pulmonary diseases if indicated)
Problems with speech and dysphagia (an assessment by a speech therapist, a referral to an ENT specialist if indicated)
Fatigue, depression, sleep disturbances (a referral to a psychologist or a psychiatric nurse if indicated, peer support, a psychiatrist may be consulted if necessary)