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This is a fragile, enveloped paramyxovirus (150-300 nm) containing
a single strand of negative-sense RNA (15 kb). It has four types
that share antigenic determinants.
Pathogenesis and Epidemiology
The virus attaches to host cells, where the envelope fuses with the
host cell membrane. The virus multiplies throughout the tracheobronchial
tree. Infection, which is transmitted by the respiratory
route, peaks in the winter, with the highest attack rates occurring
in children under 3 years old.
In this common, self-limiting condition, which usually lasts 4-5
days, children are distressed, coryzal and febrile. In young children,
hoarse coughing often alternates with hoarse crying and is
associated with inspiratory stridor secondary to laryngeal obstruction
(croup). Rarely, bronchiolitis, bronchopneumonia or acute
epiglottitis may develop, signalled by reduced air entry and
Diagnosis and Treatment
Diagnosis is clinical. Direct immunofluorescence gives rapid
results; viral isolation and reverse transcriptase nucleic acid amplification
tests (NAATs) are available as part of a respiratory virus
screen. Treatment is symptomatic (e.g. paracetamol and humidification).
Severe infection can be treated with ribavirin and humidified
Respiratory syncytial virus
This enveloped paramyxovirus (120-300 nm) containing a single
strand of negative-sense RNA attaches to host cells by 12-nm
glycoprotein spikes. There is antigenic variation within the two
types, designated A and B.
Respiratory syncytial virus (RSV) is found worldwide, infecting
children during the first 3 years of life. There are yearly epidemics
in the winter months in temperate countries and in the rainy season
in tropical countries. RSV spreads readily in the hospital environment.
Patients who are elderly and frail, and those with a compromised
respiratory tract can develop serious infection.
Coryza develops after a 4 to 5-day incubation period. In 40% of
cases bronchitis develops in older children and bronchiolitis in
the very young. Severe disease can develop quickly but, with intensive
care, mortality is very low. Children with bronchiolitis are
febrile and tachypnoeic, with chest hyperinflation, wheezing and
crepitations. Cyanosis is rare. The radiological appearances are
variable and include hyperinflation and increased peribronchial
Diagnosis and Treatment
Direct immunofluorescence or enzyme immunoassay (EIA) of
nasopharyngeal secretions is rapid. Many laboratories use
reverse transcriptase NAAT for diagnosis. The virus can be
Treatment for RSV infection is based on symptomatic relief and
humidification. Severe cases may require hospitalization and
humidified oxygen. Severely ill, immunocompromised patients
may benefit from aerosolized ribavirin.
There is no currently available vaccine.
This is a spherical enveloped virus (80-160 nm) with positive-sense
linear single-stranded RNA (27 kb); the envelope contains widely
spaced club-shaped spikes. Coronaviruses cause a coryza-like
illness similar to that of rhinovirus. The virus has been observed
in the faeces of patients with diarrhoeal disease and asymptomatic
subjects. Diagnosis is by serology using a complement fixation test
(CFT) or EIA, by detection of coronavirus-specific antigens or by
A coronavirus that emerged in China was associated with severe
pneumonia (SARS). It was transmitted by the respiratory and oral
route; mortality was approximately 10%, but higher in elderly
people and patients who were immunocompromised. Healthcare
workers were vulnerable to infection, so stringent precautions were
required to prevent hospital transmission. Coordinated infection
control has permitted eradication of the virus.
Human metapneumovirus, a paramyxovirus, has recently been
identified from children with acute respiratory tract infections. It
accounts for just under 10% of cases that occur in the winter
months, causing a clinical syndrome that is similar to RSV infection.
Dual infection with RSV is associated with severe disease.
Diagnosis is by reverse transcriptase NAAT.