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What is Aspergillosis?
Immune suppression (possibly due to concurrent diseases), stress, malnutrition, vitamin A deficiency (common with all-seed diets), confinement, and prolonged antibiotic use are all possible reasons for the development of opportunistic Aspergillus infections. Additionally, poor housing, hygiene and husbandry practices may predispose pet and aviary birds to develop this disease. Damp bedding and food, long-term food storage, humidity, poor ventilation, and inadequate cage cleaning are all factors that can increase the amount of fungal spores that are inhaled from the environment. Some kinds of bedding such as corn cob and walnut shells may also favor the growth of Aspergillus. Even in healthy individuals, inhalation or ingestion of abnormally large numbers of spores can cause severe disease. Less frequent routes of exposure include through skin lacerations or infections, or through eggshell contamination during incubation. All pet birds can develop disease, but the most commonly affected pet species are the African gray, Amazon and pionus parrots.Aspergillosis is considered one of, if not the most common, causes of respiratory disease in pet birds. It is caused by infection with a fungus of the genus Aspergillus. The species of this organism that most frequently causes respiratory disease in pet birds is Aspergillus fumigatus. This organism is found commonly in the natural environment and in fact may be found in the respiratory tract of many healthy wild and pet birds. Aspergillus makes its way into the lungs and air sacs of birds when fungal spores are inhaled from the environment. This does not normally cause a problem in fit, healthy birds, but several underlying problems and/or a massive exposure to these spores may predispose a bird to the development of aspergillosis.
What are the Signs of Aspergillosis?
Aspergillosis usually develops gradually within the lungs and air sacs (thin extensions of the avian lungs). Early signs are often subtle, including reduced energy levels, decreased appetite, lethargy, progressive weight loss, or exercise intolerance (easily out of breath). This chronic form usually is a result of long-term stress or illness and often goes on undetected for some time. Respiratory signs, such as increased respiratory rate and effort, open-mouthed breathing and respiratory noises are signs of increasing severity and are not normally detected until late in the development of disease. Respiratory distress can be an emergency in birds and can lead to rapid deterioration or sudden death. If you see these signs, alert your veterinarian as soon as possible.
Acute aspergillosis is less common and is typically seen in young, immune compromised animals that are exposed to large numbers of Aspergillus spores. This form of the disease may include any of the above signs, but progresses much more rapidly, possibly leading to death within days. Aspergillus infection may also be present in the trachea (windpipe), causing a voice change or a gurgling cough; or nasal cavity, causing facial swelling or nasal discharge.
Although aspergillosis is primarily a respiratory disease, it can affect any organ of the body by traveling through the bloodstream or by growing through an air sac into the body cavity. Because of this, there are a large number of less common signs that may be seen. Gastrointestinal signs, such as diarrhea and regurgitation or neurological signs including tremors, incoordination and generalized weakness have also been reported. Some birds go to the veterinarian with a wing droop secondary to damage to air sacs near the shoulder.
How is Aspergillosis Diagnosed?
Diagnosis of aspergillosis can be difficult and usually involves the use of several different tests. Clinical signs and physical exam findings, as well as changes on routine blood work may be suggestive of a problem, but are non-specific and not sufficient on their own for a definitive diagnosis to be reached. A history of a stressful event may also key a veterinarian into the development of aspergillosis. Radiographs are the next most common test and may show signs of changes in the lungs, air sacs, or other parts of the body. Something that may be even more useful for visualizing fungal infection in birds is endoscopy, which can be used to directly observe the airways.
All of these diagnostic methods can support a diagnosis of aspergillosis, but the disease cannot be definitively diagnosed without actually identifying the organism. Currently, the best method for arriving at a diagnosis of aspergillosis appears to be use of the above tests combined with a fungal culture of the respiratory tract. Birds with a positive culture for Aspergillus are more likely to have a significant amount of fungal growth. Cultures are, however, not incredibly sensitive and some infections may not be detected. Additionally, your veterinarian may directly observe secretions flushed from the airway or obtained during a procedure known as endoscopy to look for fungal organisms.
Recently, other tests have been developed that attempt to identify antibodies or Aspergillus organisms in the blood. These tests can be more effective at detecting Aspergillus in the body, but they are so sensitive that many animals testing positive may not actually have the disease. There are also a significant number of affected birds that test negative using these methods. Your avian veterinarian may well suggest running these tests to provide additional data, but they are unlikely on their own to provide a definitive diagnosis.
Ultimately, the best way to definitively diagnose aspergillosis is to have a pathologist observe affected tissue under a microscope. Biopsies can be taken under anesthesia, typically via endoscopy, and sent to a laboratory to be analyzed. A positive result of this test is the best possible way to be certain of a diagnosis of aspergillosis, but it is not without its limitations. Placing a debilitated bird under anesthesia can be a dangerous procedure and taking a biopsy may lead to hemorrhage or other life-threatening complications. Additionally, there is a chance that the affected tissue may be missed when the biopsy is taken. Therefore, it is not normally used as the first test. However, if your avian veterinarian suggests this procedure it is because he believes it is in your bird's best interest. This procedure may also allow for direct treatment of the fungus within the air sacs with a powerful antifungal agent.
Can Aspergillosis be Treated?
Yes. Aspergillosis can be treated with a combination of anti-fungal medication and supportive care with variable success depending on the severity and extent of disease. When considering prognosis it should be kept in mind that by the time many birds show clinical signs they likely have been sick for several weeks.
Anti-fungal medication is the first line of defense against aspergillosis, and of these medications, itraconazole is probably the most widely accepted anti-fungal drug. This medication is given by mouth and is relatively safe for use in birds. Another anti-fungal, amphotericin B, has been commonly used as a primary treatment for aspergillosis in birds when they are hospitalized, but it has been known to cause toxicity, damaging the kidneys when used for long periods. Another use for this drug is that it may be administered topically to an area of fungal growth during the endoscopic procedure, as mentioned above. There are many other anti-fungal medications that are used less frequently with varying success. Nebulization (aerosolization) of certain drugs may also be a reasonable way to treat fungal infection by allowing the drug to gain access to the airways. Anti-fungal therapy may need to be continued for at least 6 weeks and in some cases as long as 6 months in order to be fully effective.
In serious cases, surgical intervention may be necessary. Aspergillus can form granulomas (masses of fungi combined with inflammatory cells) within the airways or other parts of the body. If a granuloma forms within the trachea, it can block air flow. If this happens, the animal may need to be anesthetized so that the mass can be removed. If an airway cannot be established, veterinarians will often place an air-sac cannula (a tube leading into an air sac through the body wall) so that the bird can breathe. In many respects this is similar to the placement of a tracheostomy tube as performed in people and other mammals in emergency settings. Anesthesia of a bird with respiratory problems does carry its risks but it may be necessary if the bird cannot breathe effectively.
Aside from treating the disease itself, efforts must also be made to ensure that the bird is otherwise stable. Because of this, supportive care is an important part of treatment. Some birds may need supplemental nutrition if they are not eating. Other problems such as dehydration or hypothermia may also need to be addressed. Lastly, it is extremely important to remember that development of aspergillosis is often an indication of an underlying disease or husbandry problem. The cause of immune suppression must be addressed in order to increase the likelihood that your bird will return to health.
What is the Prognosis for a Bird Affected by Aspergillus?
The prognosis for aspergillosis varies significantly depending on the severity of the disease and when it is detected. With the dedicated care of an experienced avian veterinarian and with several days of hospitalization, a case that is diagnosed early may carry a fairly good to excellent prognosis. Unfortunately, by the time more obvious clinical signs such as respiratory effort are detected, the disease has progressed significantly. Aspergillosis is a serious disease and as it becomes more severe, prognosis becomes progressively worse, especially in birds that have significant immune compromise.
What is the Best Way to Protect against Aspergillosis?
Because Aspergillus is such a common inhabitant of the normal respiratory tract, it is impossible to entirely eliminate it. Vaccines do exist, but their effectiveness is questionable. The best prevention is based on limiting exposure to spores and keeping your bird healthy overall. Make sure your bird is in a clean environment that is not too humid or crowded. Do not leave moist bedding or food in the cage for long periods of time as these are ideal sites for fungal proliferation. Most importantly, make sure your bird is healthy and happy. Limit stress as much as possible and try to maintain routine veterinary care for your bird so that any problems that may predispose to more serious disease are detected early.
Can Aspergillosis be Transmitted to Humans?
Aspergillosis is not considered to be a contagious disease and a healthy person does not need to worry about becoming infected. Aspergillus spores are in the environment and will likely be breathed in at some point, but they rarely cause disease. One exception may be in people who have severe immune compromise. As with birds, the best way to decrease exposure to Aspergillus spores is to keep a clean home in order to limit the inhalation of fungal spores.
Reviewed by Dr. Simon Starkey D.ABVP (Avian)