Introduction to Human Nutrition

334 Introduction to Human Nutrition

Table 14.3 Characteristics of the illnesses caused by hepatitis A and norovirus

Hepatitis A (picornavirus) Norovirus (calicivirus)

Properties Particles are featureless spheres 28 nm in diameter, single-
stranded RNA coated with protein

Particles are spheres 25–35 nm in diameter, single-stranded RNA
coated with protein that has characteristic cupped surface
depressions
Infection Infection via intestine to liver, incubation period 15–20
days (mean 28 days)

Infection of intestinal lining, incubation period 24–48 h

Illness Illness from immune destruction of infected liver cells:
fever, malaise, anorexia, nausea, abdominal discomfort,
often followed by jaundice; severity tends to increase
with age: ranges from unapparent infection to weeks of
debility, occasionally with permanent sequelae

Nausea, vomiting, diarrhea, etc., lasting for 24–48 h

Shedding Shedding of virus peaks during the second half of the
incubation period (10–14 days), usually ends by 7 days
after onset of jaundice

During illness (in vomitus and feces), possibly 7 days after onset

Diagnosis Based on detection of IgM class antibody. Hepatitis A
virus in the patient’s blood serum (kits available)

Detection of virus in stool ELISA or PCR or of antibody against the
virus in patient’s blood serum; no standard methods, reagents
not readily available for most agents
Immunity Immunity is durable (possibly lifelong) after infection Apparently transient

ELISA, enzyme-linked immunosorbent assay; IgM, immunoglobulin M; PCR, polymerase chain reaction.

Exposure is by contact with infected individuals or
fecally contaminated water or other materials. Shell-
fi sh (bivalve molluscs) have been the predominant
food vehicle. Shellfi sh beds may frequently become
contaminated with human feces from sewage dis-
charges. Aerosolization of vomitus-containing virus
particles has been proposed as another mode of trans-
mission of the virus and may also be a source of food
contamination. Sensitive detection assays have now
revealed that shedding of the virus in feces may con-
tinue for up to a week after the illness subsides.

Astroviruses

Under the electron microscope, astroviruses appear as
small, round viruses that have surface projections
resembling a fi ve- or six-pointed star (Greek astron,
star). The illness differs from the norovirus in that the
incubation period is longer (3–4 days), the duration
of illness is longer (often lasting for 7–14 days), and
vomiting is less common, with diarrhea being the
predominant symptom. In addition, the very young
(<1 year) appear to be the most susceptible group,
whereas norovirus affects all age groups. Astrovirus
outbreaks have been reported to occur in crèches,
schools, hospital wards, and nursing homes, but in
many cases there was no well-defi ned mode of trans-
mission. One large outbreak linked to contaminated

food from a common supplier occurred in Osaka,

Japan, in 1991, affecting 4700 teachers and pupils

from 14 schools in the city.

Rotaviruses

Serogroup A rotaviruses are the single most impor-

tant cause of infantile gastroenteritis worldwide,

affecting an estimated 130 million infants and causing

873 000 deaths every year. The rotavirus genome

consists of 11 segments of double-stranded RNA

surrounded by a double-shelled viral capsid. When

examined by electron microscopy, the double-shelled

particles resemble a wheel-like structure morphologi-

cally (Latin rota, wheel). The incubation period of the

illness is 1–3 days, and the illness is characterized by

fever, vomiting, and diarrhea. Although the majority

of rotavirus infections involve infants, outbreaks of

food-borne, and water-borne disease affecting all age

groups have been reported, albeit infrequently.

Other viruses

Picornaviruses other than hepatitis A can also be

transmitted by the food-borne route. Polioviruses are

transmitted by food but virulent strains of this agent

are now extremely rare. Coxsackie virus and echovi-

rus have been associated with food-borne outbreaks,

but data are limited. Hepatitis E has been linked to a