"Tuberculosis is a common chronic disease of older wild and captive
birds, accounting for up to 14 percent of avian deaths in many zoological parks
with mixed species," says Dr. Nicole Van Der Heyden, veterinarian and
instructor in avian medicine at the University of Illinois College of Veterinary
Medicine in Urbana. Dr. Van Der Heyden owns and manages the Avian and Exotic
Animal Clinic of Indianapolis, Indiana.
Avian tuberculosis is more typically called avian mycobacteriosis because the
disease generally does not cause the tubercles (nodules) characteristic of the
tuberculosis found in mammals. "This chronic wasting disease is
characterized by weight loss, diarrhea, difficulty breathing, and tumors of the
skin and eyes," says Dr. Van Der Heyden. Tumors may also affect the spleen,
liver, lungs, air sacs, skin, and bone marrow.
"Mycobacteriosis is seen most frequently among parakeets, budgerigars,
Brotogeris species, Amazons, and other members of the parrot family. Commonly
infected soft-billed birds include toucans, various finches, and pigeons.
Cranes, waterfowl, poultry, rails, herons, and raptors are also prone to
infection," says Dr. Van Der Heyden.
The disease is typically transmitted when fecal matter is consumed. Waterfowl
may get the infection through their eyes from contact with contaminated water.
Most birds are more than 5 years old when the diagnosis is made.
Newly purchased birds should be screened for mycobacteriosis. The acid fast stain is currently the only laboratory method readily available for diagnosis of avian tuberculosis. Hematologic changes can increase suspicion. Since affected birds often have multi-organ involvement, intestinal shedding is common. Hence, a fecal acid fast stain serves as a useful but insensitive tool, due to intermittent shedding. Endoscopic biopsy/acid fast or bone marrow cytology is more specific.
Currently Texas A & M University and University of California at
Davis are looking at the ability of an antibody assay to detect infected birds. Initial work suggests that this will be a useful assay, but to detect all infected birds, it will have to be combined with other assays.
"Ideally, birds should be quarantined for several months to a year or more
before being introduced into a mixed aviary where a large number of birds could
be exposed. This is not feasible in most collections but should be considered
when rare or endangered species are involved," says Dr. Van Der Heyden.
"Birds maintained as pairs in easily cleaned cages are at low risk for
transmitting the disease. Frequently cage mates of infected birds never develop
the disease despite a long contact period."
Treatment of avian mycobacteriosis is controversial and may take a year or more.
According to Dr. Van Der Heyden, "In the past, concerns about transmission
to humans and lack of suitable drugs prevented most veterinarians from treating
infected birds. Recent evidence suggests that the potential for transmission is
minimal and that available drugs are effective."
Currently Texas A & M University, in collaboration with investigators at the
University of California at Davis, are seeking to develop new diagnostic assays to identify birds infected with avian tuberculosis.
Using these assays and specific management techniques, they will attempt to break the avian tuberculosis infection cycle that occurs in the red
siskin.
She comments, "Although it is unclear whether the strains of
tuberculosis that infect birds are the same that infect humans, it is prudent to
keep infected birds away from humans, particularly infants, the elderly, and
individuals with AIDS or other immune disorders."
Prevent mycobacteriosis and other diseases in your birds by practicing good
sanitation, using wire cages, changing soil and water frequently (free-flowing
water is ideal), and preventing exposure to wild birds. Stagnant ponds for water
birds should be dredged and drained annually, and free-flowing ponds should have
a virgin source of water uncontaminated by wild or captive waterfowl.
"Frequent removal of fecal material or prevention of exposure to fecal
material is the single most important factor in preventing transmission,"
says Dr. Van Der Heyden.
