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OVERVIEW

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Overview

Viral gastroenteritis (inflammation of stomach, small, and large intestine) is caused by rotaviruses, caliciviruses, astroviruses, and adenoviruses (some serotypes), which results in vomiting and/or diarrhea. In addition to the bacterial and protozoal agents responsible for approximately 20% to 25% of these cases, these viruses are a significant cause of the balance. Acute diarrheal disease is an illness, usually of rapid evolution (within several hours), that lasts less than 3 weeks. Worldwide, diarrhea caused by rotavirus resulted in an estimated 528 000 infants death in 2000, which has dropped to an estimated 21 500 in 2013 due to rotavirus vaccination. In the United States, the total annual deaths before the vaccine era used to be less than 60, but these viruses were still the major causes of severe illness and hospitalization in early life. Since the introduction of rotavirus vaccine in the United States in 2006, rotaviruses-related illness, and hospitalizations have significantly dropped and deaths are rare. Symptoms of the rotavirus disease like vomiting, abdominal cramps, and low-grade fever followed by watery stools that usually do not contain mucus, blood, or pus, are all characteristics of the acute phase of illness and can also be seen with infections due to caliciviruses, astroviruses, and adenoviruses. These viruses and their clinical diseases are described in this chapter.

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GENERAL FEATURES

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Until the 1970s, proof of viral causation of acute diarrhea was usually based on exclusion of known bacterial or protozoan pathogens and supported by feeding cell-free filtrates of diarrheal stools to volunteers to reproduce the disease. As might be expected, the results of such experiments were variable, and the methods were impractical for routine laboratory diagnosis. One aspect of such infections that proved to be of great help was the frequent association with abundant excretion of virus particles during the acute phase of illness. Virion numbers greater than 108 per gram of diarrheal stool are relatively common, allowing ready visualization with an electron microscope (Figure 15–1). Direct electron microscopy and immunoelectron microscopy were used to detect and identify the presumed causative viruses; the latter method was also be used to detect humoral antibody responses to infection. More recently, polymerase chain reactions (PCRs) and enzyme immunoassays (EIAs) are employed in diagnosis.

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Viral diarrhea was a diagnosis of exclusion

Many viral particles seen in stool by electron microscopy

Diagnosis confirmation by PCR or EIA

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FIGURE 15–1.

Viruses of diarrhea. All are photographed at the same magnification to illustrate the size and morphologic differences. A. Rotavirus. B. Calicivirus. C. Astrovirus. (Courtesy of Claire M. Payne.)

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Several criteria were used to establish the role of viruses in diarrheal diseases, including detecting viruses in symptomatically ill patients more frequently than in asymptomatic individuals, demonstrating significant antibody response in patients shedding the virus, reproducing the disease by experimental inoculation ...

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