Aspergillosis is a non-contagious, opportunistic fungal infection. It is caused by Aspergillus
spp., a mold found commonly throughout the environment. Aspergillus
is so common in fact, that most healthy chickens regularly breathe 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.
Aspergillosis Clinical Signs
There are a wide range of clinical signs presented in birds with aspergillosis. This is because they vary depending on how the chicken became infected, where lesions develop in their body, organ(s) involved, and their overall health status (immune system). Aspergillosis may be acute or chronic in nature.
- Acute form: Generally occurs in young chicks and results in high morbidity and mortality. Onset is very quick and usually develops within a week. Most affected birds will die within a few days without emergency veterinary care. The most common signs include:
- Loss of appetite
- Difficulty breathing
- Cyanosis (bluish/purplish comb)
- Chronic form: Usually very subtle in onset, and it may take several weeks or months to develop. It is most common in older birds, many with 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. The most common clinical signs observed include:
- Change in behavior
- Weight loss
- Reduced appetite
- Exercise intolerance
- Increased respiratory rate
- Changes in vocalization (voice), often more apparent in roosters
- Audible respiratory sounds
- Tail bobbing
- Open-mouthed breathing
Aspergillosis Contributing Factors
- Pre-existing disease
- Exposure to damp feed, droppings, and bedding
- Hot and humid weather conditions
- 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
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.
How Aspergillosis is Diagnosed
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---through obtaining a culture or endoscopy.
Aspergillosis Treatment Options
Aspergillosis treatment varies depending on the underlying cause and can often be very difficult. Therapy generally
consists of 4 to 6 months of antifungal therapy, nebulization, 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.