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CHAPTER 15 Viruses of 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 are a significant cause of the balance. Rotaviruses, caliciviruses, astroviruses, and some adenoviruses are considered here. GENERAL FEATURES 1. 2. 3. 4. 5. 6. 7. Viral diarrhea was a diagnosis of exclusion Many viral particles seen in stool by electron microscopy Confirmation by EIA or PCR is now possible Multiple criteria used for establishing etiologic relationship Rotaviruses, caliciviruses, astroviruses, and adenoviruses are established "Candidate" viruses meet some criteria Vomiting commonly follows short incubation period ROTAVIRUSES 1. The human intestinal rotaviruses were first found in 1973 by electron microscopic examination of duodenal biopsy specimens 2. Most common cause of winter gastroenteritis in children <2 years of age I. VIROLOGY 1. 2. 3. 4. 5. 6. 7. 8. Double-stranded RNA viruses are shaped like a wheel Antigenic types are based on capsid proteins VP4 and VP7 ISVP is infectious not the whole virion RNA-dependent RNA polymerase directs the synthesis of mRNA and genomic RNA by using negative strand RNA of the double stranded RNA genome Virus assembly takes place at the endoplasmic reticulum Animal rotaviruses produce diarrhea but interspecies spread not demonstrated in nature Reassortment of the 11 RNA segments readily occurs Live vaccines can incorporate genes from animal viruses II. HUMAN ROTAVIRUS INFECTIONS A. EPIDEMIOLOGY 1. Primarily infants and children in colder months 2. Most older children and adults are immune B. PATHOGENESIS 1. Destroys villus cells of jejunum and duodenum 2. Absorptive surface is decreased 3. Enterotoxin-like effects are also present C. IMMUNITY 1. Type-specific humoral and secretory IgA antibodies are protective 2. IgA and mucin glycoproteins confer protective role of breastfeeding II. ROTAVIRUS INFECTIONS: CLINICAL ASPECTS A. MANIFESTATIONS 1. After an incubation period of 1 to 3 days, there is usually an abrupt onset of vomiting, followed within hours by frequent, copious, watery, brown stools 2. The major complications result from severe dehydration, occasionally associated with hypernatremia. 3. This complication can lead to death, particularly in very small or malnourished infants B. DIAGNOSIS 1. Electron microscope or EIA detect virus C. TREATMENT AND PREVENTION 1. Vigorous replacement of fluids and electrolytes is required in severe cases and can be life-saving 2. Control consists of rigorous hygienic measures, including careful hand washing and adequate disposal of enteric excretions 3. Live attenuated, or reassortant vaccines are available and recommended for infants CALICIVIRUSES 1. First associated with an outbreak in Norwalk, Ohio and called the Norwalk agent I. VIROLOGY 1. Small, round, naked, icosahedral capsid RNA viruses are hardy 2. Two genera: Norovirus and Sapovirus 3. Several serotypes but not yet grown in cell or organ culture II. CALICIVIRUS INFECTIONS A. EPIDEMIOLOGY 1. Sharp outbreaks include older children and adults 2. Transmission is by fecal–oral route B. PATHOGENESIS 1. Both pathogenesis and pathology are similar to rotaviruses 2. Enterotoxic features are not present C. IMMUNITY 1. Reinfection can occur with same serotypes III. CALICIVIRUS INFECTIONS: CLINICAL ASPECTS 1. The incubation period is 10 to 51 hours, followed by abrupt onset of vomiting and diarrhea 2. Clinical picture and diagnostic tests are similar to rotavirus 3. No treatment or vaccine exists ADENOVIRUSES, ASTROVIRUSES, AND "CANDIDATE" VIRUSES I. Adenoviruses 1. Some adenoviruses, most of which are exceedingly difficult to cultivate in vitro, are now recognized as significant intestinal pathogens 2. Serotypes 40 and 41 are commonly found II. Astroviruses 1. Astroviruses have a shape that resembles a 5- or 6-pointed star 2. Naked capsid, positive-sense RNA viruses 3. Illness is often, but not always, mild III. “Candidate” Viruses 1. Coronavirus-like agents 2. Toroviruses 3. Group A coxsackieviruses