Lancaster farming. (Lancaster, Pa., etc.) 1955-current, February 24, 1996, Image 31

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    INCLUSION BODY
HEPATITIS: A
RE-EMERGING DISEASE
Barrett S. Cowen
M.S., Ph.D.
Dept of Vet Science
Wiley Lab
Inclusion body hepatitis (IBH)
is an economically important dis
ease of commercial chickens,
especially broilers, which was first
reported in the USA in 1963.
It was described as a necrotizing
hepatitis in 7-week-old chickens
associated with intranuclear inclu
sion bodies in hepatocytes. Subse
quently, it was shown that the dis
ease was associated with fowl ade
novirus (FAV) infection.
IBH has been recognized in
numerous countries/regions of the
wwld and is reappearing as an
important contemporary poultry
health problem. It is characterized
by a sudden onset of mortality
which peaks in 3-4 days and usual
ly stops by the Sth day.
However, mortality occasional
ly continues for 2-3 weeks. Mor
bidity is low and sick chickens are
in what seems to be a crouching
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position with ruffled feathers and
die within 48 hours or recover.
Historically, mortality has usually
been no more than 10 percent, but
occasionally can be as high as 30
percent However, this feature has
changed in the last 10 years. IBH
usually is observed in broilers 3-7
weeks of age, but it had been
reported in chickens as young as
seven days of age and as old as 20
weeks of age.
Twelve serotypes (to date) of
FAV have been isolated from
chickens. Numbers of FAV have
been isolated from both healthy
and diseased flocks and this has
resulted in differing opinions
regarding their role as pathogens.
There have been variable results
when attempting to reproduce IBH
with FAV isolates and marked dif
ferences in virulence have been
demonstrated among isolates of
the same and differing FAV
serotypes.
Numerous field and experimen
tal studies have emphasized a pre
disposing role for infectious bursu
al disease (IBD) and chicken infec
tious anemia (CIA) in IBH.
Additionally, other studies have
shown that simultaneous infection
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of chickens with FA V and rhieiryn
anemia agent (CAA) resulted in
hepatitis and anemia, a condition
which corresponds well with the
IBH that was seen in the 1960 s and
19705.
Based on field and experimental
evidence pointing to FAV acting
as secondary pathogens (that is, as
a result of primary immunosup
pression) in a multifactorial dis
ease (for example, IBDV+CAA +
FAV ss IBH), it is not surprising
that the use of IBD vaccines mark
edly reduced outbreaks of IBH in
the USA and other areas of the
world.
In the late 1980 s, a previously
unknown disease having many
similarities to IBH spread through
out Pakistan. The disease initially
was observed almost exclusively
in 3-6 week old broilers, although
it has occasionally been seen in
breeder pullets and layers. It is
characterized by the accumulation
of straw-colored fluid in the heart
sac, severely affected liver and
kidney, minimal morbidity, and
20-75 percent mortality. The heart
lesion gave rise to the name
“hydropericardium syndrome
(HPS),” but it could well be a dif
ferent form of IBH because the
important signs, gross lesions, and
histological changes associated
with HPS are very similar to IBH.
At about the same time a HPS
like disease was reported in Mex
ico; hepatitis, hydropericardium,
and high mortality being common
features. This disease, which was
reported as IBH, has subsequently
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been observed in Venezuela,
Ecuador, Peru, and Chile. HPS has
also been recently reported in Iraq,
Kuwait, and India.
Many of the IBH/HPS out
breaks in these widely separated
regions of the world have been
found to be associated with ser
otype 4 FAV. The fact that there
has been higher mortality and a
much higher incidence of hydro
pericardium associated with these
IBH/HPS outbreaks than has been
die case, historically, with classi
cal IBH (that is, primary or concur
rent immunosuppression: secon
dary IBH) supports the need for a
better understanding and know
ledge of this disease syndrome.
In addition to the apparent
changes in the clinical and patho
logical features of IBH during the
past decade, new field and experi
mental findings have demon
strated that FAV can be primary
pathogens. For example, there
have been peracute IBH outbreaks
(in broilers 7-21 days of age) in
Australia and New Zealand in
which there is no evidence of con
current IBD and/or CIA.
Serotype 8 FAV were common
ly isolated from affected flocks in
both of these locations. Vaccina
tion of broiler breeders with ser
otype 8 FAV in Australia has suc
cessfully protected broilers against
peracute IBH outbreaks. What is
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the significance of the changes
observed in this disease syndrome
and associated causative agents
during die past decade? Are there
increasing numbers of highly
pathogenic FAV arising in nature?
Do some of FAV serotypes
(e.g., serotype 4) have greater ttop
ism for certain organs (e.g., the
heart) than other isolates/
serotypes, or ate they mote viru
lent and heart-associated when
interacting with other agents (e.g.,
IBDV and/or CAA)?
The fact that this disease syn-
is changing and spread
ing should be of concern for the
poultry industry of the USA, as
well as other countries, as trade
barriers are rapidly disappearing
(for example, NAFTA). It is
imperative that research on these
syndromes and their associated
disease agents be initiated so that
poultry diagnosticians can rapidly
recognize and distinguish these
syndromes (if differences truly do
exist) and will have the means
(e.g., vaccines) to control them.
Research on IBH has been ini
tiated at the Animal Diagnostic
Laboratory at Penn State Universi
ty and will initially be focused on
observing and comparing the clini
cal and pathological features ol
this disease syndrome in experi
mentally inoculated chickens.