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Reoviruses are medium-sized viruses with a double-stranded, segmented RNA genome. The family includes human rotaviruses, the most important cause of infantile gastroenteritis around the world (Figure 37-1). Acute gastroenteritis is a very common disease with significant public health impact. In developing countries, it is estimated to cause as many as 1.3 million deaths of preschool children annually, of which rotavirus is responsible for up to about 500,000 deaths. In the United States, acute gastroenteritis is second only to acute respiratory infections as a cause of disease in families.
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Caliciviruses are small viruses with a single-stranded RNA genome. The family contains noroviruses, the major cause of nonbacterial epidemic gastroenteritis worldwide. Astroviruses also cause gastroenteritis.
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REOVIRUSES AND ROTAVIRUSES
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Important properties of reoviruses are summarized in Table 37-1.
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Structure and Composition
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The virions measure 60–80 nm in diameter and possess two concentric capsid shells, each of which is icosahedral. (Rotaviruses have a triple-layered structure.) There is no envelope. Single-shelled virus particles that lack the outer capsid are 50–60 nm in diameter. The inner core of the particles is 33–40 nm in diameter (Figure 37-2). The double-shelled particle is the complete infectious form of the virus.
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The reovirus genome consists of double-stranded RNA in 10–12 discrete segments with a total genome size of 16–27 kbp, depending on the genus. Whereas rotaviruses contain 11 genome segments, orthoreoviruses and orbiviruses each possess 10 segments and coltiviruses have 12 segments. The individual RNA segments vary in size from 680 bp ...