Page 354 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com 2 mebooksfree.com DNA Polymerase CHAPTER 41 Hepatitis Viruses 343 mebooksfree.com
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TABLE 41–2 Important Properties of Hepatitis Viruses
Replication
HBsAg in
Virus
in Virion
Defective
Genome
Virus Family
Envelope
ssRNA
HAV
No
Picornavirus
No
No
1
dsDNA
HBV
Yes
Hepadnavirus
Yes
No
No
Flavivirus
No
No
ssRNA
HCV
HDV
ssRNA
Yes
Deltavirus
Yes
No
HEV
ssRNA
No
Calicivirus
No
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ds = double-stranded; ss = single-stranded.
1
Interrupted, circular dsDNA.
2
Circular, negative-stranded ssRNA.
Important Properties
HAV is a typical enterovirus classified in the picornavirus
The pathogenesis of HAV infection is not completely
family. It has a single-stranded RNA genome and a nonen-
understood. The virus probably replicates in the gastroin-
veloped icosahedral nucleocapsid and replicates in the
cytes are infected, but the mechanism by which cell damage
cytoplasm of the cell. It is also known as enterovirus 72. It
occurs is unclear. HAV infection of cultured cells produces
has one serotype, and there is no antigenic relationship to
HBV or other hepatitis viruses. testinal tract and spreads to the liver via the blood. Hepato-
no cytopathic effect. It is likely that attack by cytotoxic
T cells causes the damage to the hepatocytes. The infection
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Summary of Replicative Cycle
is cleared, the damage is repaired, and no chronic infection
ensues. Hepatitis caused by the different viruses cannot be
HAV has a replicative cycle similar to that of other entero-
viruses (the replicative cycle of poliovirus is discussed in
The immune response consists initially of IgM antibody,
Chapter 40).
which is detectable at the time jaundice appears. It is there-
fore important in the laboratory diagnosis of hepatitis A.
Transmission & Epidemiology
The appearance of IgM is followed 1 to 3 weeks later by the
HAV is transmitted by the fecal–oral route. Humans are the
production of IgG antibody, which provides lifelong
reservoir for HAV. Virus appears in the feces roughly 2 weeks
protection.
before the appearance of symptoms, so quarantine of patients
is ineffective. Children are the most frequently infected
Clinical Findings
group, and outbreaks occur in special living situations such
as summer camps and boarding schools. Common-source
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mebooksfree.com mebooksfree.com mebooksfree.com The clinical manifestations of hepatitis are virtually the mebooksfree.com
same, regardless of which hepatitis virus is the cause
outbreaks arise from fecally contaminated water or food
(Table 41–3). Fever, anorexia, nausea, vomiting, and jaun-
such as oysters grown in polluted water and eaten raw.
dice are typical. Dark urine, pale feces, and elevated trans-
Unlike HBV, HAV is rarely transmitted via the blood,
because the level of viremia is low and chronic infection does
aminase levels are seen. Most cases resolve spontaneously
not occur. About 50% to 75% of adults in the United States
in 2 to 4 weeks. Hepatitis A has a short incubation period
(3–4 weeks) in contrast to that of hepatitis B, which is 10 to
have been infected, as evidenced IgG antibody.
TABLE 41–3 Clinical Features of Hepatitis Viruses
Available
Carriers
Virus
Useful
Used for Diagnosis
HAV Mode of Transmission Chronic Laboratory Test Usually Vaccine Immune Globulins
Yes
Fecal–oral
No
IgM HAV
Yes
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Yes
Yes
Blood, sexual, at birth
HBsAg, HBsAb, IgM HBcAb
Yes
HBV
1
Yes
No
HCV Ab
HCV
No
Blood, sexual
HDV
Blood, sexual
Yes
None
HEV
Fecal–oral
No
No
No
Ab = antibody; Ag = antigen.
1
Sexual transmission seems likely but is poorly documented.
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