What is aspergillosis?
Aspergillosis is a fungal infection that commonly causes respiratory disease in pet birds. It can cause upper respiratory tract disease (nose, sinuses, eye, syrinx, and trachea), lower respiratory tract disease (lungs and air sacs — a specialized part of the respiratory tract in birds), secondary bacterial infections and internal organ disease.
What is Aspergillus?
Aspergillus is the fungal organism that causes aspergillosis. The most common species is Aspergillus fumigatus. 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 is found everywhere in the environment as microscopic spores, particularly in soil, moist nesting material, and moldy foods. The spores persist in the environment and are resistant to disinfection.
Aspergillus is an environmental contaminant and is not contagious from bird to bird. It most commonly affects birds that have compromised immune systems due to other diseases, a dirty environment, or chronic malnutrition. However, various other factors can suppress a bird’s immune system and may lead to a secondary infection with Aspergillus, including:
- Steroid use
- Long-term antibiotic use
- Excessive stress
- Poor husbandry or hygiene
- Respiratory irritants (e.g., cigarette smoke)
- Viral infections
- Other chronic infections
A bird with a healthy immune system that is exposed to Aspergillus spores may not develop an infection, but it is possible, especially if the bird is exposed to large numbers of spores. Birds on all-seed diets may be more prone to this disease because all-seed diets lack vitamin A, a nutrient essential for the health of a pet bird’s respiratory tract and immune system.
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
- Coughing
In advanced stages of disease, signs may include:
- Lethargy, listlessness (low activity)
- Fluffed feathers
- Weight loss
How is aspergillosis diagnosed?
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. 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 X-rays may reveal pneumonia, thickening of air sacs, a breakdown of sections of bone, or tissue-dense material in the opening of the trachea.
- Serology (antibody) tests look for antibodies against Aspergillus, but the results can sometimes be misleading. A negative result does not always rule out infection because birds with weakened immune systems may not produce enough antibodies to detect. A positive result does not always confirm infection either, since healthy birds are commonly exposed to Aspergillus in the environment and may naturally have antibodies to the fungus.
- DNA tests can 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.
- Surgical laparoscopy is the most accurate diagnostic technique. In this technique, a fiber-optic endoscope is passed surgically into the bird’s airways to view the trachea, syrinx, air sacs, and/or lungs. Samples of lesions are collected for microscopic analysis and a culture may be submitted to a veterinary laboratory for identification. In most cases, the tissue is sent to a pathologist for identification of the presence or absence of fungal elements.
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 challenging disease to treat and even more difficult to cure. The body attempts to “wall off” the fungus with a type of scar tissue, which makes it difficult for antifungal drugs 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, vitamin A injection, and treatment of other underlying or concurrent diseases. In many cases, referral to an avian specialist is advised.
