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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
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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
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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