7-12. CAUSATIVE AGENTS
Of the several viruses capable of producing hepatitis, four are considered to be
the most predominant causative agents of the disease today. These agents are:
a. Hepatitis A virus (HAV).
b. Hepatitis B virus (HBV).
c. Hepatitis D virus (HDV, "Delta Hepatitis").
d. Hepatitis Non-A, Non-B (NANB).
7-13. HEPATITIS IMMUNOLOGICAL MARKERS
Testing for the specific type of viral hepatitis involved in the disease process is
based on detecting certain possible viral antigens present in the patient's serum as well
as the detection of specific antibodies produced in the immune response to the viral
agent. Antibodies associated with viral hepatitis are either IgM or IgG immunoglobulins.
IgM immunoglobulins are involved in the primary immune response and serve as good
immunological test markers of recent or acute infection since they appear at the onset
of the infection and are fairly short lived. IgG immunoglobulins usually appear at about
the same time as IgM but result in a longer sustained response and generally serve as
good immunological markers of past exposure and possible immunity. The most
common methodology utilized to detect the serological markers of hepatitis is the
Section IV. HEPATITIS A VIRUS
7-14. VIRUS STRUCTURE
The hepatitis A virus (HAV) is a small nonenveloped, single-stranded RNA virus
that belongs to the picornavirus class of viruses. It consists of an outer capsid containing
the hepatitis A antigen. The capsid surrounds the single strand of RNA and the viral
protein genome (VPG). The VPG aids the virus in attaching to the host cytoplasmic
ribosomes for self-replication (figure 7-3).