Biomedical Engineering Reference
In-Depth Information
The clinical and laboratory findings for viral hepatitis
are the same for all of these agents, in varying degrees, with
elevated serum enzyme levels of aspartate and alanine
aminotransferases and
g
-glutamyltransferase being the
most consistent. The serological markers now available for
all but one of the human agents are the most important
diagnostic tests.
(
World Health Organization, 2008
). There has been
a drastic decline in the number of infected individuals since
a national HBV elimination strategy was implemented in
the USA in 1991. Between 6% and 10% of infected indi-
viduals become chronic carriers, many of whom will
develop hepatocellular carcinoma and may die from
cirrhosis (
Alter, 1982
). Hepatitis B has been reported to be
the most frequently occurring laboratory-associated infec-
tion, with an incidence of up to seven times that seen in the
general population in some categories of
Hepatitis A
The hepatitis A virus (HAV) causes what was formerly
known as infectious hepatitis. This agent is a unique
picornavirus, currently grouped with the enteroviruses
(
Purcell et al., 1984; Robertson, 2001
).
Serological tests, which can be quantitated to differen-
tiate between the acute and convalescent phases, are
available for antiHAV IgM, which is positive only during
the acute phase, and for anti-HAV IgG, which persists and
confers lifelong immunity after infection.
More than 100 human cases of hepatitis A associated
with newly imported chimpanzees (Pan troglodytes) have
been reported (
Centers for Disease Control, 1971
), and
sporadic cases still occur from contact with experimentally
infected animals. Naturally occurring HAV has also been
reported in newly imported owl monkeys (Aotus trivirgatus)
(
LeDuc et al., 1983; Lemon et al., 1990
), in African green
monkeys, cynomolgus macaques (
Shevtsova et al., 1988
),
and rhesus monkeys (
Lankas and Jensen, 1987
).
laboratory
workers (
Pike, 1976
).
Transmission of HBV, found in blood, saliva, semen
(
Scottetal.,1980
), cerebrospinal fluid, and urine (
Vil-
larejos et al., 1974
), is by parenteral inoculation, droplet
exposure of mucous membranes, and contact exposure of
broken skin. Since the virus may be stable in dried blood
or blood components for several days, the potential for
entry through inconspicuous breaks in the skin from
environmental surfaces must not be ignored (
Lauer et al.,
1979
).
The hepatitis B status of an individual can be deter-
mined by testing for serological markers. HBsAg: The
hepatitis B surface antigen is present only in acute or
chronic infection. Anti-HBs: The antibody to HBsAg is
found in convalescent or immunized individuals. Vaccines
produce only anti-HBs because there is no viral replication.
Anti-HBc: The antibody to the hepatitis B core antigen is
indicative of virus replication and appears in the acute
phase after HBsAg. It persists with HBsAg in chronic
carriers and with anti-HBs in convalescent individuals. If
anti-HBc is present without HBsAg or anti-HBs, the indi-
vidual must be considered a carrier.
Prevention
Biosafety Level 2, with special emphasis on
hand washing and personal hygiene, is recommended for
work involving contact with feces from animals and people
known to be or potentially infected with HAV. A safe,
effective hepatitis A vaccine is available and is recom-
mended for all those working with animals experimentally
infected with hepatitis A. For postexposure prophylaxis,
a single dose of 0.02 ml/kg immune serum globulin (ISG)
should be given as soon as possible, but within 2 weeks
after exposure (
Centers for Disease Control, 1991
).
Prevention
Biosafety Level 2 facilities are adequate for
containment of these agents. Safe, effective vaccines for
HBV are available, and all human healthcare and chim-
panzee contact workers should be given the immunization
series of three injections (at 0, 1, and 6 months). The
asymptomatic carrier state exists in chimpanzees and
gorillas in the wild (
Linnemann et al., 1984
), thus the
hepatitis B status of all captive chimpanzees should be
determined so that carriers can be identified and properly
handled. A hepadnavirus causing severe hepatitis in
a woolly monkey has been documented but experimental
inoculation into a chimpanzee did not result in an active
infection (
Lanford, et al., 1998
). This may be a useful
nonhuman primate animal model of the human disease.
Hepatitis B
Hepatitis B, caused by the human hepadnavirus (HBV),
reproducibly infects only humans and apes, and chimpan-
zees are the only suitable animal models (
Tabor et al.,
1983
), although gibbons (Hylobates spp.) have been used
(
Scott et al., 1980
). The woodchuck hepatitis virus and the
hepadnaviruses of other species, including ground squirrels
and Pekin ducks, do not infect people.
Hepatitis B, formerly known as “serum hepatitis,” is an
important human disease with approximately 2 billion
people infected world wide, with 360 million living with
chronic disease. Between 500 000 and 700 000 infected
individuals die annually of hepatitis B complications
Hepatitis C
After tests for serological markers of both hepatitis A and B
were developed and transfusion blood was routinely tested
to remove units with hepatitis B infectivity, it became
