Poliovirus infection (poliomyelitis) Poliomyelitis occurs when a susceptible individual is infected with poliovirus type 1, 2 or 3. These viruses have a propensity for the nervous system, especially the anterior horn cells of the spinal cord and cranial nerve motor neurones. Poliomyelitis is found worldwide but its incidence has decreased dramatically following improvements in sanitation, hygiene and the widespread use of polio vaccines. Spread is usually via the faecal-oral route, as the virus is excreted in the faeces.
The incubation period varies from 7 to 14 days. Although polio is essentially a disease of childhood, no age is exempt. The clinical manifestations vary considerably:
NAPPARENT INFECTION is common and occurs in 95% of infected individuals.
ABORTIVE POLIOMYELITIS occurs in approximately 4- 5% and is characterized by the presence of fever, sore throat and myalgia. The illness is self-limiting and of short duration.
NON-PARALYTIC POLIOMYELITIS has features of abortive poliomyelitis as well as signs of meningeal irritation, but recovery is complete.
PARALYTIC POLIOMYELITIS occurs in approximately 0.1% of infected children (1.3 % of adults). Several factors predispose to the development of paralysis:
• male sex,
• exercise early in the illness,
• trauma, surgery or intramuscular injection which localize the paralysis,
• recent tonsillectomy (bulbar poliomyelitis) This form of the disease is characterized initially by features simulating abortive poliomyelitis. Symptoms subside for 4-5 days, only to recur in greater severity with signs of meningeal irritation and muscle pain, which is most prominent in the neck and lumbar region. These symptoms persist for a few days and are followed by the onset of asymmetric paralysis without sensory involvement. The paralysis is usually confined to the lower limbs in children under 5 years of age and the upper limbs in older children, whereas in adults it manifests as paraplegia or quadriplegia.
BULBAR POLIOMYELITIS occurs in 5-30% and is characterized by the presence of cranial nerve involvement. Soft palate, pharyngeal and laryngeal muscle palsies are common. Aspiration pneumonia, myocarditis, paralytic ileus and urinary calculi are late complications of poliomyelitis.
POST-POLIO SYNDROME refers to an increase in the degree of muscle atrophy of an affected limb many years after the primary attack.
The diagnosis is a clinical one. Distinction from the Guillain- Barre syndrome is easily made by the absence of sensory involvement and the asymmetrical nature of the paralysis in poliomyelitis. Laboratory confirmation and distinction between the wild virus and vaccine strains is achieved by virus culture, neutralization and temperature marker tests.
Treatment is symptomatic. Bed rest is essential during the early course of the illness. Respiratory support with intermittent positive pressure respiration is required if the muscles of respiration are involved. Once the acute phase of the illness has subsided, occupational therapy, physiotherapy and occasionally surgery play an important role in patient rehabilitation.
PREVENTION AND CONTROL
Immunization has dramatically decreased the prevalence of this disease worldwide. Trivalent oral poliovaccine (OPV) (active virus) is used (see Information box 1.2); occasionally, inactivated poliovirus vaccine is used intramuscularly. Coxsackievirus. echovirus and enterovirus infection These viruses are spread by the faecal-oral route. They each have a number of different types and are responsible for a broad spectrum of disease involving the skin and mucous membranes, muscles, nerves, the heart, and rarely other organs, such as the liver and pancreas. Skin and oropharyngeal disease There is a vesicular eruption on the fauces, palate and uvula (herpangina). The lesions eventually evolve into aphthous ulcers. The illness is usually associated with fever and headache but is short-lived, recovery occurring within a few days. Hand, foot and mouth disease Oral lesions are similar to those seen in herpangina but may be more extensive in the oropharynx. Vesicles and a maculopapular eruption also appear, typically on the palms of the hands and the soles of the feet, but also on other parts of the body. This infection commonly affects children; recovery occurs within a week. Neurological disease Other enteroviruses in addition to poliovirus can cause a broad range of neurological disease, including meningitis, encephalitis, and a paralytic disease characteristic of poliomyelitis. Heart and muscle disease Enteroviruses are an important cause of acute myocarditis and pericarditis, from which, in general, there is complete recovery. However, these viruses can also cause chronic congestive cardiomyopathy and, rarely, constrictive pericarditis. Skeletal muscle involvement, particularly of the intercostal muscles, is an important feature of Bornholm disease, a febrile illness usually due to Coxsackievirus B. The pain may be of such an intensity as to mimic pleurisy or an acute abdomen. The infection affects both children and adults and may be complicated by meningitis or cardiac involvement. Rhinovirus infection Rhinoviruses are responsible for the common cold; peak incidence rates occur in the colder months, especially spring and autumn. There are multiple rhinovirus immunotypes, which makes vaccine control impracticable. In contrast to enteroviruses which replicate at 37°C, rhinoviruses grow at 33°C, the temperature of the upper respiratory tract, which explains the localized disease characteristic of common colds.
Reovirus infection occurs mainly in children, causing mild respiratory symptoms and diarrhoea. A few deaths have been reported following disseminated infection of brain, liver, heart and lungs. Rotavirus infection Rotavirus (Latin rota = wheel) is so named because of its characteristic circular outline with radiating spokes. It is responsible worldwide for both sporadic cases and epidemics of diarrhoea, and is presently one of the most important causes of childhood diarrhoea. The prevalence is higher during the winter months. Other viruses associated with gastroenteritis Clinically the illness is characterized by vomiting, fever, diarrhoea, and the metabolic consequences of water and electrolyte loss. Histology of the jejunal mucosa in children shows shortening of the villi, with crypt hyperplasia and mononuclear cell infiltration of the lamina propria.
Diagnosis can be established by ELISA for the detection of rotavirus antigen in faeces but this is rarely indicated clinically, since infection is self-limiting and there is no specific treatment. Treatment is directed at overcoming the effects of water and electrolyte imbalance with adequate oral rehydration therapy and, when indicated, intravenous fluids. Antibiotics should not be prescribed. Adults may become infected with rotavirus but symptoms are usually mild or absent. The virus may, however, cause outbreaks of diarrhoea in patients on geriatric wards. Rotavirus vaccines are under evaluation. Live, attenuated, oral bovine rotavirus vaccines (R1T 4237 and WC3) are moderately effective in the industrialized world but less so in the developing world. Reassortant rotaviruses are being constructed by recombinant DNA technology that have an attenuated animal rotavirus ‘backbone’ but contain RNA inserts from human rotavirus in an attempt to improve immunogenicity.