RESPIRATORY SYNCYTIAL VIRUS
VIROLOGY
Respiratory syncytial virus (RSV) is classified as a
pneumovirus within the paramyxo-virus family. Its name is derived from its
ability to produce cell fusion in tissue culture (syncytium formation). Unlike
influenza or parainfluenza viruses, it possesses no hemag-glutinin or
neuraminidase. The RNA genome is nonsegmented, negative sense, and single
stranded and codes for at least 10 different proteins. Among these are two
matrix (M) proteins in the viral envelope. One forms the inner lining of the
viral envelope; the func-tion of the other is uncertain.
The antigens on the surface spikes of the viral
envelope include the G glycoprotein, which mediates virus attachment to host
cell receptors, and the fusion (F) glycoprotein, which induces fusion of the
viral envelope with the host cell surface to facilitate entry. F glycoprotein
is also responsible for fusion of infected cells in cell cultures, leading to
the appearance of multinucleated giant cells (syncytium formation). Antibodies
directed at the F glycoprotein are more efficient than anti-G glycoprotein
antibodies in neutraliz-ing the virus in vitro.
At least two antigenic subgroups (A and B) of RSV are
known to exist. This dimor-phism is due primarily to differences in the G
glycoprotein. The epidemiologic and bio-logical significance of these variants
is not yet certain; however, epidemiologic studies have suggested that group A
infections tend to be more severe. RSV is the single most important etiologic
agent in respiratory diseases of infancy, and it is the major cause of
bronchiolitis and pneumonia among infants under 1 year of age.
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