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A34-Lancatwr Arming, Sirturday. -April 13, 1996
ASPERGILLOSIS
IN POULTRY
Patty Dunn, DVM
Animal Diagnostic Lab
Dept of
Veterinary Science
Infections caused by fungi
(molds) are relatively sporadic, but
important diseases of poultry and
most other species of birds.
By far the most common fungal
infection in birds is known as
“aspergillosis,” which is caused by
the mold species Aspergillus
Fumigatus. Birds appear to be
much more susceptible to fungal
infections than mammals, probab
ly due to differences in their respir
atory and immune systems as well
as die unique features of their
propagation and housing.
The following are common
questions and answers pertaining
to aspergillosis in poultry.
• What kind of poultry are
affected? Chickens, turkeys and
ducks can all be affected, although
chickens seem to be the most resis
tant of the three. Very young birds
(less than three weeks of age) are
most often affected, but older
market turkeys and turkey breed
ers also tend to develop" clinical
aspergillosis. As with other respir
atory infections, males tend to
react mote severely than females,
which is due to the stresfjof their
faster growth and heavier muscle
mass.
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• How do birds get infected with
Aspergillus? Inhalation of large
numbers of mold spdres appears to
be the primary route of exposure.
Spores are the propagative stage of
the mold and can be likened to
small, round microscopic “seeds,”
each capable of producing new
mold growth if “landing” on
material or tissue that can support
its growth. Moldy litter, grain,
feed, dust and contaminated eggs
and hatcheiy equipment are the
common sources of the mold.
Shavings from hard wood tend to
support the growth of A. Fumiga
tus better than those from soft
wood (pines).
• What environmental condi
tions favor the growth of Aspergil
lus Fumigatus in the hatcheiy and
poultry house? Many of the condi
tions that favor growth of other
microorganisms such as bacteria
are also good for fungus. Aspergil
lus Fumigatus prefers a relatively
humid, warm environment, abun
dant oxygen and plant-based subs
trates (wood shavings, feed). In the
poultry house, litter and spilled,
moist feed are excellent substrates.
Although the pelleting process
destroys most mold present in feed
or feed ingredients, fungal spores
can recontaminate the finished
feed, particularly if it becomes
wet. Fungus can then grow and
spread rapidly. Unfortunately, A.
Fumigatus can also grow inside of
eggs that may have been contami
nated from the environment in the
breeder house. Egg incubation
temperatures and humidity are
very favorable for growth of the
mold. If these eggs are broken in
the hatchery, millions of spores
can contaminate the immediate
surroundings and newly hatched
chicks will likely develop severe
aspergillosis.
• What kind of clinical signs are
seen in infected birds? Because
the fungus primarily affects the
respiratory tract, most signs are
related to that system. Labored,
rapid breathing and gasping with,
outstretched necks are common
symptoms. Decreased activity,
increased thirst and stunted growth
are additional symptoms. Ascites
may develop in meat type birds
secondary to lung damage. Less
frequendy, Aspergillus Fumigatus
can infect the eye or brain, causing
eye swelling and neurologic signs.
Total mortality during a flock
infection is generally less than 10
percent, but can be as high as SO
percent in complicated cases. The
onset of clinical signs is often
noticed from one to three weeks of
age. Hence, aspergillosis is some
times called “brooder
pneumonia.”
• What internal lesions are seen
in affected birds? In very young
birds, small, yellow caseous
nodules or disks can be found in
the lungs, adjacent air sacs, and
occasionally in the trachea or
bronchi where they obstruct air
flow into the lungs. Older growing
or mature turkeys often have
extensive plaques of yellow mater
ial in the air sac walls. Occasional
ly in the air sacs actual blue-greeu/
gray “fuzzy” mold can be seen. In
the ocular form, caseous nodules
are present in the conjunctival sac
in the inside comer of the eye or
elsewhere under the eyelids. In the
nervous form, portions of the brain
contain yelloty or red
discoloration.
• How is the disease diagnpsed?
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Clinical signs and lesions
described above are good clues in
identifying the infection. Howev
er, the lesions can resemble those
caused by certain bacterial dis
eases (E. coli infections, pullorum
disease, etc.), and further testing at
a diagnostic laboratory may be
necessary to confirm the fungal
infection. Fungal cultures and
microscopic examination of
affected tissues are two common
laboratory test methods, that are
relatively rapid for confirmation of
aspergillosis.
• How can aspergillosis be
treated? Unfortunately, there is no
direct medication against this fun
gal infection that can be mass
applied. Antibiotics have no effect,
except if a concurrent bacterial
infection is present. Severely
affected birds should be culled,
and ventilation should be optim
ized to decrease ammonia and
dust. In pet birds and expensive
zoological species of birds,
aggressive therapy with injectable,
oral, or nebulized antifungal medi
cations can be effective. This is
sometimes coupled with surgery to
remove obstructive fungal masses
from the upper respiratory
urways.
• What are some management
practices that help prevent asper
gillosis? In the breeder house, any
techniques employed to ensure
clean hatching eggs (clean, dry
nests, frequent egg collection, low
house humidity) and good shell
strength will help keep down fun-
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gal contamination. Egg storage
facilities should be clean and sur
faces dry. Care should be taken
during transport of eggs to minim
ize cracks and breakage. In the
hatchery, setting only clean, intact
hatching eggs is extremely impor
tant. Strict hatchery sanitation pro
cedures including the use of disin
fectants and fumigants with known
antifungal activity are necessary to
decrease numbers of fungal organ
isms invariably present in the
environment
Most hktcheries routinely moni
tor for fungus and bacteria in the
incubators and hatchers. In the
poultry house, control measures
include thorough cleaning, anti
fungal disinfection and complete
drying of the house between
flocks, particularly in the brooding
areas; use of high quality, clean,
dry soft wood shavings as litter;
thorough cleaning, disinfection
and drying of feed handling equip
ment (bins, augers, pans); prevent
ing any wet areas caused by water
leakage from water lines, drinkers,
etc.; optimizing ventilation to
decrease relative humidity and
remove dust and gasses; and
avoiding overcrowding of birds.
As in many poultry'diseases, a var
iety of factors may predispose the
onset of aspergillosis. Strict atten
tion to sanitation and eliminating
favorable conditions for fungal
growth both in the hatchery and at
the farm are keys to reducing the
risk of aspergillosis in your poultry
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