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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.

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