Page 333 - Review of Medical Microbiology and Immunology ( PDFDrive )

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PART IV Clinical Virology
322
Transmission & Epidemiology
hyperimmune globulins against RSV may be more
Transmission occurs via respiratory droplets and by direct
effective.
contact of contaminated hands with the nose or mouth.
RSV causes outbreaks of respiratory infections every win-
Prevention
ter, in contrast to many other “cold” viruses, which reenter
the community every few years. It occurs worldwide, and
killed vaccine resulted in an increase in severity of symp-
virtually everyone has been infected by the age of 3 years.
RSV also causes outbreaks of respiratory infections in hos-
toms. Passive immunization with a monoclonal antibody
directed against the fusion protein of RSV (palivizumab,
pitalized infants; these outbreaks can be controlled by There is no vaccine. Previous attempts to protect with a
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handwashing and use of gloves, which interrupt transmis-
Synagis) can be used for prophylaxis in premature or
sion by hospital personnel.
immunocompromised infants. Hyperimmune globulins
(RespiGam) are also available for prophylaxis in these
Pathogenesis & Immunity
comial outbreaks can be limited by handwashing and use
RSV infection in infants is more severe and more often
of gloves.
involves the lower respiratory tract than in older children
and adults. The infection is localized to the respiratory
tract; viremia does not occur.
PARAINFLUENZA VIRUSES
The severe disease in infants may have an immuno-
pathogenic mechanism. Maternal antibody passed to the
Diseases
infant may react with the virus, form immune complexes,
These viruses cause croup (acute laryngotracheobronchitis),
and damage the respiratory tract cells. Trials with a killed
vaccine resulted in more severe disease, an unexpected
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disease resembling the common cold in adults.
finding that supports such a mechanism.
Most individuals have multiple infections caused by
Important Properties
RSV, indicating that immunity is incomplete. The reason
for this is unknown, but it is not due to antigenic variation
The genome RNA and nucleocapsid are those of a typical
of the virus. IgA respiratory antibody reduces the fre-
paramyxovirus (see Table 39–1). The surface spikes con-
quency of RSV infection as a person ages.
sist of hemagglutinin (H), neuraminidase (N), and fusion
(F) proteins (see Table 39–4). The fusion protein mediates
Clinical Findings
the formation of multinucleated giant cells. The H and N
In infants, RSV is an important cause of lower respiratory
tract diseases such as bronchiolitis and pneumonia. RSV is
rate spike. Both humans and animals are infected by para-
also an important cause of otitis media in young children.
influenza viruses, but the animal strains do not infect
In older children and young, healthy adults, RSV causes proteins are on the same spike; the F protein is on a sepa-
humans. There are four types, which are distinguished by
respiratory tract infections such as the common cold and
antigenicity, cytopathic effect, and pathogenicity (see
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bronchitis. However, in the elderly (people older than 65
later). Antibody to either the H or the F protein neutral-
years of age) and in adults with chronic cardiopulmonary
izes infectivity.
diseases, RSV causes severe lower respiratory tract disease,
including pneumonia.
Replication is similar to that of measles virus (see page 318).
Laboratory Diagnosis
An enzyme immunoassay (“rapid antigen test”) that detects
Transmission & Epidemiology
the presence of RSV antigens in respiratory secretions is
These viruses are transmitted via respiratory droplets.
commonly used. The presence of the virus can be detected
by immunofluorescence on smears of respiratory epithe-
months.
lium or by isolation in cell culture. The cytopathic effect in
cell culture is characterized by the formation of multinucle- They cause disease worldwide, primarily in the winter
Pathogenesis & Immunity
ated giant cells. A fourfold or greater rise in antibody titer
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is also diagnostic. A reverse transcriptase polymerase chain
These viruses cause upper and lower respiratory tract
reaction (RT-PCR) test is also available.
disease without viremia. A large proportion of infections
Treatment
causes of croup. Parainfluenza virus 3 is the most com-
Aerosolized ribavirin (Virazole) is recommended for
mon parainfluenza virus isolated from children with
lower respiratory tract infection in the United States.
severely ill hospitalized infants, but there is uncertainty
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