Avian
Tuberculosis: The Disease
and Its
Management
By Darrel K. Styles, MS, DVM
If
your birds are suspected of having avian TB, you and you alone, are responsible
for the health of your flock. Your failure to take all necessary precautions in
managing avian TB in your birds and facilities may expose you and your flock to
significant risk. The sale or transfer of your birds to any other person or
facility -without a full disclosure and acknowledgement of the TB risk may
expose you to personal liability in the event one of your birds infects other
"clean" birds or infects individuals susceptible to the avian TB
bacterium.
Avian
Tuberculosis or avian TB is caused by a bacterium, usually
Mycobacterium
avium or Mycobacterium genavense. This disease
causes a
wide range of clinical signs such as "going lite" yet having a
voracious appetite; depression, fluffing, occasionally masses under the skin,
and typical "sick bird syndrome". In advanced disease, neurological
signs may be observed such as Imbalance, weakness, and inability to walk, perch,
or fly. This organism is found everywhere in the environment including soil and
water. It is shed from wildlife including our native avifauna. However,
some species of
birds may be
particularly susceptible to infection through mechanisms not completely
understood. The stressors found in captivity may have some bearing on the
disease.
We
are experiencing a problem of unknown magnitude with this disease. Many or most
of individual flocks have had at least one case of avian TB diagnosed by
pathological examination. And therein lies the problem; there are currently no
reliable diagnostic tests for avian TB in the live bird. Most diagnoses are made
on tissues of dead specimens. This disease may be carried "occultly",
meaning hidden, by a bird displaying no signs of clinical illness. When this
'carrier' becomes stressed from transport, overcrowding, or reproductive
demands, it may begin to shed the organism and cause disease to itself and
others around it. The bacteria are passed through the droppings and can live for
an extended period outside the body. Any excretion from the bird may
carry the
organisms. [Remember the old "Don't Spit on the Sidewalk" signs from
the early part of the 20th century?] Therefore, by the time the diagnosis is
made, avian TB may have already infected some or all of the exposed birds.
Therefore, there is a tremendous need for reliable diagnostic tests in the live
bird.
The
only tests most veterinarians have at their disposal for live birds
are
cultures, blood tests, and special stains. The special stain is called the
acid-fast stain. This stain is usually performed on tissues or droppings. Avian
tuberculosis bacteria stain positively on acid-fast staining (£. coli and many
other bacteria do not stain positively on the acid-fast test). However, there
are other bacteria unrelated to TB that may stain positively on acid-fast, but
these are uncommon
in avian
species. Therefore, if acid-fast organisms are observed, especially in a bird
displaying signs of clinical illness, then z presumptive diagnosis of
tuberculosis is made. The diagnosis may be confirmed by culture. Culture
requires special laboratory conditions and the samples are usually sent to USDA
labs for identification and typing. These results can take literally months to
be returned.
Culture
is expensive and time consuming. Neither culture nor staining will detect the
organisms in birds that are not actively shedding the organisms. Blood tests are
sufficiently sensitive enough or may only suggest infection. There are many
infected carrier birds that do not shed or only periodically shed the bacteria.
Therefore, an infected bird may not necessarily be detected by these methods.
This is usually the case.
In
response to this need for diagnostic aids, prominent research institutions are
beginning the development of diagnostic tests for the live bird.
How
then are we to manage this disease? We may try two approaches, husbandry and
treatment by drugs. Experimental drug regimens have been developed that you may
employ in your aviary, but only with the assistance of your avian veterinarian.
We do not know how effective these drug regimens may be since we are still
trying to develop the diagnostic tests to measure the success of treatment.
However, these regimens have been employed in other avian species and clinical
improvement has resulted. You may have your avian veterinarian contact me by
email or phone if you wish to pursue drug therapy with a flock experiencing a
confirmed outbreak. This information will only be dispensed to a licensed
practicing avian veterinarian in your state. All treatment will be done
at YOUR
expense.
However,
regardless of whether you decide to treat your flock, if
you have had
a case of avian TB diagnosed by culture or histopathology in your flock, then
you will need to implement the following management changes. These suggestions
are meant only to serve as guidelines and are written for the most stringent
standards of precaution. You will have to amend them to fit your particular
situation. Please understand that this is a manageable disease if the proper
precautions are taken. These guidelines are written according to stringent
standards and you may have to tailor them to suit your unique situation. The
guidelines are:
Husbandry
and Management of the Infected Flock
1.
Do not move any birds into or out of the aviary where the exposure
occurred. By the time you have discovered the tuberculosis infection, it has
likely been present for a long time. If you attempt to move "apparently
healthy" birds out of the aviary, you will only succeed in spreading the
infection to a new location.
If you move
new birds into the aviary because the deaths have ceased, you will only serve to
infect the new additions and may precipitate another outbreak.
2.
Isolate the infected
aviary from other birds, food and
caging
materials. Ideally, the outbreak occurred in a freestanding building that can be
isolated. But if it occurred in a room, treat that room as if it were a
freestanding building. There should be no food sources in the infected aviary
unless those sources are specifically for those birds in that aviary. Also, you
should remove no inanimate objects such as caging, perching, or food/water
dishes unless you thoroughly disinfect the objects by scrubbing with soap and
water, followed by a fresh bleach soak, then rinse and allow to completely dry
in the sun at full exposure to light. You should feed and clean that aviary last
in your circuit, and preferably, have a footbath (which is refreshed daily) and
a pair of coveralls dedicated
only to that building. Try to service the infected aviary only once daily if
possible; don't make additional trips into the aviary. Ideally, a separate
person who has no contact with other birds should attend to this aviary.
3.
Reduce stress and improve the environment for the birds in the infected
aviary. Stress causes an increase in the rate of shedding of the bacteria and
will precipitate outbreaks. Overcrowding the birds in cages of inadequate size
will compound this stress. Stress also results from demands of breeding and many
outbreaks are observed during the breeding season. The following are suggestions
in helping to reduce stress outbreaks of TB:
a) Keep
only one pair in a cage of adequate size in the breeding season.
b) If you
flock birds in the non-breeding season, do so in sufficiently large cages with
low numbers of birds segregated by sex. Immediately remove any bird that appears
to be stressed or abused from the group cage.
c) Do not
stack cages unless installed in a proper rack system
with true
physical barriers between cages (not just paper) that shield
from
excrement.
d) Space
cages sufficiently apart or physically screen them to
reduce
stress from aggression and to inhibit the movement of bacteria laterally.
e) Increase
light and ventilation within the aviary while maintaining a proper ambient
temperature.
f) Ensure
that all nutritional needs are met with a balanced
diet.
g) Ideally,
these birds should be kept in large well-screened
flights where they endure lowered levels of stress and achieve maximum
reproductive success.
4.
Understand that we are managing a flock of birds that
all may be
potentially infected with tuberculosis. Outbreaks occur most often during the
breeding season. Demands on parent birds during reproduction are immense, and
stress levels increase.
This often leads to an active infection and the chicks act as
"amplifiers" of the outbreak since their immune systems are not
sufficiently mature enough to combat the bacteria. This is why it is of extreme
importance to keep the population density low in a room with good ventilation.
Keeping the concentration of bacteria in the air to a minimum will help to
prevent spread of the infection. It has been shown that a tuberculosis organism
can live up to 4 hours suspended in air, so it is quite resilient.
5.
Separate chicks from the adult birds as soon as they
are weaned.
The chicks may cause overcrowding and stress if left with the parents too long.
Apply the same rules, of cage inhabitants as with adults. Just because the birds
are young or siblings, doesn't mean that you can crowd them into small cages.
6.
Take personal precautions. When cleaning and servicing
the aviary,
it would be ideal to wear a face-mask and goggles or glasses to prevent
eye-splash. Also, individuals with compromised immune systems should not have
exposure to the birds. People with compromised immune systems would include
individuals with HIV, transplant patients, individuals on chemotherapy for
cancer, or anyone taking high doses of corticosteroids. The Center for Disease
Control in Atlanta considers this a ubiquitous organism, meaning found
everywhere in the environment. In a paper by Horsburgh et al. [I], Environmental
Risk Factors for Acquisition of Mycobacterium avium Complex in Persons with
Human Immunodeficiency Virus Infection;
"Several other important potential sources of MAC (Mycobacterium avium
Complex) were not associated with disease. These include contact with soil,
having a bird, knowing a
person with
MAC, and having been hospitalized."
People
with normally functioning immune systems have a high resistance to this
infection. The bacteria are already in the environment due to shedding from
wildlife. However, we do urge at risk individuals to take proper precautions and
avoid contact or expo
sure.
We
are left with the dilemma of chicks that may potentially be infected with avian
TB. Your ethical responsibility is to notify the person purchasing or accepting
the birds that the possibility of this infection exists. I suggest that you make
a written statement of acknowledgement signed by both parties so that you reduce
your liability.
We
hope that our drug treatment regimens will be effective. But
again, until
we develop the diagnostic tests, we will not know for sure. Therefore, follow
these guidelines the best you can to ensure
reduced
outbreaks of disease in your aviary.
[1]
Horsburgh, C. Robert, et al. Environmental Risk Factors for
Acquisition
of Mycobacterium avium Complex in Persons with Human Immunodeficiency Virus
Infection; The Journal of Infectious
Diseases,
1994; 170: 362-367.
