Aspergillosis in Birds
Aspergillosis is a fungal infection that commonly causes respiratory disease in pet birds. It can cause both upper respiratory tract (nose, sinuses, eye, and trachea) and lower respiratory tract (lungs and air sacs—a specialized part of the respiratory tract in birds) disease and create secondary bacterial infections or internal organ disease.
What is Aspergillus?
Aspergillus is the fungus that causes aspergillosis. This slow-growing fungal infection gradually damages tissues in the respiratory tract or other internal organs over weeks to months, often with little evidence of illness until an organ or system is severely compromised. Aspergillus fungus exists in the environment as microscopic spores that are found everywhere, particularly in soil, moist nesting material, and moldy foods. The spores persist in the environment and are very resistant to disinfection.
"The spores persist in the environment and are very resistant to disinfection."
Aspergillus is an environmental contaminant and is not contagious from bird to bird. It more commonly affects birds with compromised immune systems from other diseases or malnutrition. Birds with healthy immune systems may be exposed to Aspergillus spores and not develop an infection. However, even healthy birds exposed to large numbers of spores may become infected. Steroid use, long-term antibiotic use, excessive stress, poor husbandry or hygiene, respiratory irritants (e.g., cigarette smoke), viral infections, and other chronic infections can all cause immune suppression and lead to secondary infection with Aspergillus.
Birds on all-seed diets may be more prone to this disease because seed diets lack vitamin A, a nutrient essential to keeping both the respiratory tract and immune systems of pet birds healthy and more resistant to a fungal infection.
What are the clinical signs of aspergillosis in birds?
Birds with aspergillosis may show non-specific signs, and the infection may not be apparent early in the disease. Infected birds may show respiratory signs, including tail bobbing, difficulty breathing, and coughing. The bird may be lethargic, fluffed, listless, and lose weight.
A veterinarian familiar with birds will start an assessment by collecting a complete history, measuring your bird’s weight, and performing a thorough physical examination. Since many clinical signs of aspergillosis are non-specific and common to several different diseases, your veterinarian may recommend several tests to determine which disease is causing your bird’s symptoms.
How is aspergillosis diagnosed?
Many different tests may be employed if aspergillosis is suspected. Each test provides another piece of the puzzle, and multiple tests are often needed to give more clarity.
A complete blood count (CBC) with a dramatic elevation in white blood cells may initially raise suspicion of an Aspergillus infection.
Radiographs (X-rays) may only show subtle lesions in the early stages of the disease. Later in the illness, changes visible on radiographs may include material in the lumen of the trachea, pneumonia, thickening of air sacs, and a breakdown of sections of bone.
Serology (antibody) tests are available but can have false negative results because a healthy immune system is needed to mount an antibody response. Many birds with aspergillosis have poorly functioning immune systems. Likewise, as Aspergillus spores are common in the environment, many healthy birds can have antibodies to this fungus, so false positive serology tests may also occur.
DNA tests will detect the presence of Aspergillus DNA in blood or other tissues. A tracheal wash may document the presence of the Aspergillus organism in the trachea or respiratory tract, however, spores may be present in small numbers, even in healthy birds.
The most accurate diagnostic technique is surgical laparoscopy, in which a fiber-optic endoscope is passed surgically into the bird’s airways to view the trachea, air sacs, lungs, and sinuses. Samples of lesions are collected for microscopic analysis and culture at a veterinary laboratory.
"The most accurate diagnostic technique is surgical laparoscopy..."
How is aspergillosis treated?
Good hygiene, frequent cage cleaning, fresh and nutritious food, and good ventilation are all necessary for treating and preventing outbreaks of aspergillosis in birds.
Aspergillosis is a very challenging disease to treat and even more difficult to cure. The location of the fungal infection and the way the body attempts to wall off the fungus with a type of scar tissue restrict the anti-fungal drugs’ ability to get to the fungal organisms. Treatment may take weeks to months and often requires hospitalization at the beginning. The bird must have a robust immune system to eliminate the organism entirely.
Treatments may include oral, intravenous, topical, and aerosolized antifungal medications. Surgical removal of fungal plaques (concentrated areas of fungal growth) may be attempted but is dangerous unless performed by an experienced avian surgeon. Supportive care includes hospitalization, oxygen therapy, warmth, force-feeding, administration of anti-inflammatory medications, and treatment of other underlying or concurrent diseases. In many cases, referral to an avian specialist is advised.
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