What are paramyxoviruses and how they affect us

MEASLES (RUBEOLA)

Measles is caused by a paramyxovirus which spreads by droplet infection. One attack confers a high degree of immunity. Most people suffer from measles in childhood, and a mother who has had the disease confers passiva immunity on her infant for the first 6 months of life. In tropical countries and on a background of malnutrition measles can be very severe, with a high mortality. The incubation period is about 10 days to the commencement of the catarrhal stage.

Clinical features (see the information box)

Catarrhal stage

There is a febrile onset, with nasal catarrh, sneezing, redness of the conjunctivae and watering of the eyes. In addition, cough, hoarseness of the voice and photophobia usually appear by the second day.

At this stage, a diagnosis of measles may be made from the presence of Koplik's spots on the mucous membrane of the mouth. These are small white spots surrounded by a narrow zone of inflammation. The disease is highly infectious during the catarrhal stage and the child is miserable and irritable.

Exanthematous stage

After 3 or 4 days Koplik's spots disappear and the red macular or maculo-papular rash develops, first at the back of the ears and at the junction of the forehead and the hair. Within a few hours there is invasion of the whole skin and as the spots rapidly become more numerous they fuse to form the characteristic blotchy appearance of measles (see Fig. 2.2, p. 64). The rash fades after several days into a faint brown staining followed by a fine desquamation. The malaise and the fever subside as the rash fades. As with most infectious diseases, measles is more severe in older children and adults.

Complications

These are listed in the information box.

Management

The patient should be isolated if possible and excluded from school for 10 days from the appearance of the rash. Most patients, in spite of the high temperature, remain uncomplicated and antibiotics should be prescribed only for bacterial Complications.

Prevention

Active immunisation

There is a highly effective live attenuated measles vaccine (usually given in association with mumps and rubella vaccines, as 'MMR vaccine). In the UK it is recommended that children should receive two doses: shortly after their first birthday and prior to school entry. In countries where measles is epidemic there may be a case for earlier immunisation, but if it is given too early, residual maternal antibody may diminish vaccine efficacy.

Passive immunisation

Human normal immunoglobulin, given intramuscularly, is used for the prevention or attenuation of measles in contacts under 18 months of age and for non-immune debilitated children, especially those with malignant disease. The dose is 250 mg for children under 1 year old, 500 mg for those 1-2 years old, and 750 mg over 3 years.

MUMPS

Mumps is spread by droplet infection and affects mainly children of school age and young adults. The infectivity rate is not high and there is serological evidence that 30 40% of infections are clinically unapparent. The incubation period is about 18 days.

Clinical features

Malaise, fever, trismus and pain near the angle of the jaw are soon followed by tender swelling of one or both parotid glands. Parotid swelling alone is often the first feature. The submandibular salivary glands may also be involved. The swollen glands subside in a few days, and may be succeeded by swelling of a previously unaffected gland. Acute lymphocytic meningitis is another mode of presentation and is the most common form of extra-salivary gland involvement; encephalomyelitis is rare. Orchitis occurs in about 1 in 4 males who develop mumps after puberty; it is usually on one side only, but if it is bilateral, sterility may be a sequel. Obscure abdominal pain may be due to pancreatitis or oophoritis.

Investigations

Most cases of mumps can be diagnosed on clinical grounds alone but, if in doubt, the diagnosis can be confirmed by the demonstration of specific antibodies; alternatively, the virus may be cultured from the saliva, or from the cerebrospinal fluid in meningitis. Differential diagnosis is from salivary calculus, which is unilateral, and sarcoidosis, which causes bilateral chronic parotitis.

Management

Apart from the relief of symptoms, no other treatment is necessary. Orchitis can be relieved by prednisolone (40 mg orally daily for 4 days).

Prevention

Mumps vaccine is given in two doses with measles and rubella vaccines (MMR) shortly after the first birthday and prior to school entry.

RESPIRATORY SYNCYTIAL VIRUS

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract infection in infants and young children. It produces yearly epidemics and during these RSV can be isolated from nearly 90% of children admitted to hospital with lower respiratory tract disease. Most children are infected within their first 2–3 years. (By age 2, 95% are seropositive.)

Clinical features

RSV produces upper respiratory tract infection (nasal congestion, pharyngitis) which, particularly with primary infection in infants (in 30–80%), progresses to lower respiratory tract infection with bronchiolitis and pneumonia.

Cough, often paroxysmal, is a prominent symptom. Bronchiolitis is characterised by wheezing and hyperinflation of the lungs. Infection in older children and adults is frequently symptomatic, including secondary and repeated infections; upper respiratory tract infection and tracheobronchitis are common but lower respiratory tract illness is uncommon in these groups.

Management

There are several rapid diagnostic techniques for instance, t hose based on immunofluorescence of throat washings or swabs; serology is unhelpful for hospital diagnosis. For young children admitted to hospital with lower respiratory tract infection supportive respiratory care is important. Ribavirin given as a small-particle aerosol (by tent, mask or ventilator for 12-18 hours a day for 3-7 days) has been shown to improve arterial oxygen saturation and clinical outcome in severe RSV bronchiolitis.

Prevention

Maternal antibody does not protect infants and repeated infection occurs in older children and adults despite previous infection. A killed vaccine introduced in the 1960s was associated with worse disease when the recipients encountered natural infection. This has suggested that the immune response may somehow contribute to the pathogenesis of natural RSV infection, and there is still no vaccine for RSV.

PARAINFLUENZA VIRUSES

These are associated with upper respiratory tract infections colds, croup, otitis media and conjunctivitis, and with lower respiratory tract infections-tracheobronchitis, bronchiolitis and pneumonia.