There are four serotypes of parainfluenza viruses: parainfluenza 1, 2, 3, and 4. These en-veloped viruses belong to the paramyxovirus group; contain nonsegmented, negative-sense, single-stranded RNA; and, like the influenza viruses, possess a neuraminidase and hemag-glutinin. Their mode of spread and pathogenesis is similar to that of the influenza viruses. They differ from the influenza viruses in that RNA synthesis occurs in the cytoplasm rather than the nucleus. In addition, the antigenic makeup of the four serotypes is relatively stable, and significant antigenic shift or drift does not occur. Each serotype is considered separately.
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