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Avian Tuberculosis (Mycobacterium avium)
PDD Syndrome
 
Description:

Mycobacterium (ATB) - Straight or slightly curved, non motile rods, 0.2­0.6 x 1.0 µm. Although difficult to stain, rods are Gram positive. After staining with basic fuchsin, cells resist decolorization with acidic­ethanol and are therefore termed acid­alcohol­fast bacilli (AFB). This characteristic is due to the high level of lipid in mycobacterial cell walls.

There are seventy­one validly named species of Mycobacterium and an additional three sub­species The principal pathogens in the genus are M. bovis, M. leprae and M. tuberculosis but, in all, thirty­two species are known to be pathogenic to humans or animals. Species of Mycobacteria other than those above are often referred to as "atypical mycobacteria". The most commonly encountered pathogens among the atypical mycobacteria are species of the Mycobacterium avium complex. The M. avium complex (MAC) its considered to contain M. avium, M. avium subspecies paratuberculosis, M. avium subspecies silvaticum and M. intracellulare. However, poorly identified strains which show some similarity to M. avium are also frequently, and incorrectly, allocated to the complex. There are over 20 recognized serotypes within the M. avium complex.

Most birds including parrots, parakeets, cranes, sparrows, starling, emus, waterfowl raptors and softbills, have shown susceptibly to M. avium. It is believed that favorable conditions virtually all species of birds are susceptible to avian tuberculosis. It is most prevalent where there is a high population density, such as in zoos, or collections of birds.

Transmission:

M. avium infections are considered to be "open" meaning infected birds consistently shed large amounts of organism into the environment.

M. avium is transmitted by ingestion and inhalation of aerosolized infectious organisms from feces. Incubation in birds is weeks to years. Oral ingestion of food and water contaminated with feces is the most common method of infection. Once ingested, the organism spreads throughout the bird's body and is shed in large numbers in the feces. If the bacterium is inhaled, pulmonary lesions may develop. Skin invasion may occur as well. The spread via infected eggs can occur, but it is not common.

The transmission of M. avium from human to human has not been convincingly demonstrated and all infections are thought to be of environmental origin.
Symptoms:

In some cases sudden death can occur in a bird with normal body weight and outer appearance. However, in most cases a bird with TB will develop symptoms such as progressive weight loss in spite of a good appetite, depression, diarrhea, increased thirst, and respiratory difficulty. A decreased in egg production often occurs in birds that were laying eggs. Once the disease appears, it is virtually impossible to eradicate it. Eventual death is the usual outcome

Birds with the intestinal form often present with chronic wasting disease - and Proventricular Dilatation Syndrome is often one of the suspected possible diseases. In addition to weight loss, depression, diarrhea, increased urination (polyuria), abdominal distention, lameness and difficulty in breathing may be present.
Prevention: Preventing M. avium is best done by minimize stress and overcrowding; Provide proper ventilation; Prevent malnutrition with a proper diet. Controlling an M. avium outbreak in zoos, bird gardens and private aviaries can be especially difficult to eradicate. New additions to the aviary should be quarantined for a minimum of 1-2 months. Testing new additions for M. avium is also a good way to prevent possible outbreaks.
Treatment: All M. avium isolates that have been tested up to now are totally resistant to the antituberculous drugs currently used in humans ATB is extremely difficult to treat, and in many cases treatment is not considered a viable option.
Diagnosis:

It is difficult and lengthy process to culture the M. avium organism in the lab. An elevated White blood cell count may be present, as well as a low red blood cell count. It is sometimes possible to find bacteria in the feces by staining procedures. This however, is not specific because other acid-fast bacteria that are not M. avium may also be present.

At ABI we use two techniques for testing M. avium. PCR assays which detect the actual disease causing organism, and ELISA assays which detect specific antibodies for M. avium. PCR assays are considered to be the fastest most sensitive method for detecting M. avium while ELISA assays help determine exposure to M. avium.
Sample: At postmortem, biopsy of the liver, digestive tract, spleen and lungs. Is one of the best ways to diagnose the disease. For general screening whole blood, serum, vent and throat swabs can be used. It is best to submit both blood and swab samples for testing.
Handling: Prior to shipping samples should be stored at 4 C. Samples must be shipped overnight in a transport medium or as a dry swab.
Limitations:
References:
 
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