Aspergillosis is a non-contagious, opportunistic fungal infection caused by Aspergillus
, a common type of mold. Aspergillus
is so common in fact, that most healthy chickens regularly breath in Aspergillus
spores every day without getting sick. However, if birds have an impaired immune system or living in stressful conditions then they are at an increased risk of developing Aspergillosis. Aspergillosis primarily infects the respiratory tract, however any organ system may be affected.Aspergillus fumigatus
is the most common species isolated from infected birds, followed by A. flavus
, A. nidulans
, and A. amstelodami
Aspergillosis can present very differently in affected birds. Clinical signs are variable, and depend on how the chicken was infected, the organs involved, and their health status. Aspergillosis commonly develops in both acute and chronic forms of the disease.
- Acute form: Acute aspergillosis is a serious, often fatal respiratory disease. It is more likely to occur in young chicks or immunocompromised chickens inhale excessively high levels of Aspergillus spores from the environment. Onset of the acute form is very quick---along with the disease course. Most affected birds will die within a few days without emergency veterinary care. The most common signs associated with acute aspergillosis are lethargy, depression, loss of appetite, difficulty breathing, cyanosis (bluish/purplish comb), abdominal enlargement (due to ascites), polyuria, and polydipsia.
- Chronic form: Chronic aspergillosis is usually very subtle in onset, with non-specific clinical signs initially observed. Most affected birds are older and have a history of malnutrition, stress, concurrent illness, or prolonged antibiotic/corticosteroid use. The entire course of the disease ranges from less than 1 week to over 6 weeks in duration. Common early signs include weight loss despite a good appetite, exercise intolerance, reduced activity level, decreased appetite, or change in behavior. Once the disease advances towards the later stages of infection then more specific signs pertaining to the affected organ system(s) occur. When the respiratory system is involved, chickens often develop airsacculitis, resulting in increased respiratory rate, changes in vocalization (such as a rooster's crow), audible respiratory sounds, open-mouthed breathing, and tail bobbing.
- Immunosuppression is one of the main predisposing factors.
- Pre-existing disease
- Poor sanitary practices. Aspergillus grows in damp feed, droppings, and bedding. Therefore keeping chickens in an environment which exposes them to these conditions regularly puts them at risk.
- Hot and humid weather conditions.
- Stress. Stress is a strong immune suppressor. Any events which cause stress can increase a chicken's susceptibility to disease. Example events include attempted predator attacks, fighting among flock members, exposure to very cold or hot temperatures, mishandling, etc.
- Prolonged use of antibiotics and/or corticosteroids.
- Poor ventilation. Aspergillus can accumulate in high concentrations in the air, as inhalable dust particles.
- Overcrowding birds.
Aspergillosis is not a transmissible disease. Chickens are infected through environmental exposure. Aspergillus
are opportunistic invaders, and healthy birds are usually resistant to infection unless they are exposed to a massive number in the environment or are vulnerable due to age, concurrent illness, chronic inflammatory condition or stress. Sometimes multiple flock members become infected at the same time from exposure to the same source.
A presumptive diagnosis of aspergillosis can usually be made based on the chicken's medical history, clinical signs, physical exam and complete blood count (CBC). Radiographs may also be needed, which will help show the location and severity of the Aspergillus
lesions in the lungs and air sacs of the birds. Although, these lesions will only be seen during the later stages of the infection.
In order for your veterinarian to obtain a definite diagnosis of aspergillosis, they will need to collect some samples to send off to a diagnostic laboratory, to confirm the presence of Aspergillus
in the bird---by conducting a fungal culture, cytology, or histopathology.
Treatment for chickens with aspergillosis consists of 4 to 6 months of antifungal therapy, modification of the environment, and supportive care. There are several types of antifungal drugs used for treating aspergillosis in chickens, some more effective then others. Since affected birds are at increased risk of developing a secondary bacterial infection, they are often concurrently put on antibiotics.