Chapter 15: Viruses of Diarrhea

INTRODUCTION

Viral gastroenteritis (inflammation of stomach, small, and large intestine) is caused by rotaviruses, caliciviruses, astroviruses, and adenoviruses (some serotypes), which results in vomiting or diarrhea. Acute diarrheal disease is an illness, usually of rapid evolution (within several hours), that lasts less than 3 weeks. In addition to the bacterial and protozoal agents responsible for approximately 20% to 25% of these cases, viruses mentioned above are a significant cause of the balance. These viruses, including rotaviruses, caliciviruses, astroviruses, and some adenovirus serotypes are described below.

GENERAL FEATURES

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 in an attempt 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 have been used frequently to detect and identify the presumed causative viruses; the latter method could also be used to detect humoral antibody responses to infection. More recently, polymerase chain reactions (PCRs) and enzyme immunoassays (EIAs) have been increasingly employed in diagnosis.

Detection of a specific virus in the stools of symptomatic patients is not sufficient to establish the role of the virus in causing disease. Other criteria to be fulfilled include the following:

1. Establish that the virus is detected in patients who are ill significantly more frequently than in asymptomatic, appropriately matched controls, and that virus shedding temporally correlates with symptoms.

2. Demonstrate significant humoral or secretory antibody responses, or both, in patients shedding the virus.

3. Reproduce the disease by experimental inoculation of nonimmune human or animal hosts (usually the most difficult criterion to fulfill).

4. Exclude other known causes of diarrhea, such as bacteria, bacterial toxins, and protozoa.

Using these criteria, four groups of viruses have been clearly established as important causes of gastrointestinal disease: rotaviruses, caliciviruses, astroviruses, and some adenovirus serotypes (“enteric” adenoviruses). Other viruses have also been implicated, but many of the preceding criteria have not been fulfilled; ...