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Aspergillosis

Bronchomycosis, Pneumomycosis

Overview


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.

Clinical Presentation


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.

Risk Factors


  • 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.
  • Malnutrition
  • Poor ventilation. Aspergillus can accumulate in high concentrations in the air, as inhalable dust particles.
  • Overcrowding birds.

Transmission


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.

Diagnosis


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


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.

Clinical Signs

Loss of or reduction in vocalizing
Difficulty breathing
Open-mouthed breathing
Tail bobbing
Audible respiratory sounds
Abnormal crackles or clicking noises
Nasal discharge
Increased thirst
Reduced appetite
Weight loss
Lethargy
Increased time spent laying down
Isolation from flock members
Green color in urates in feces

Diagnosis

  • History
  • Complete blood count (CBC)
  • Fungal culture - taken of the throat, trachea or air sacs
  • Cytology
  • Endoscopy
  • Radiography
  • CTScan
  • Histopathology
  • Postmortem exam - Often based on observation of white caseous nodules in th

Treatment

NameSummary
Supportive careIsolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.
Itraconazole10 mg/kg administered orally, twice a dayK Marx
Amphotericin B1 mg/kg administered IT, TID + 1.5 mg/kg IVK Marx
Terbinafine hydrochloride10-15 mg/kg PO q12-24h with IatraconazoleK Marx
Ketoconazole60 mg/ml
Tarwood (Loxostylis alata) extract200 mg/kgM Suleiman, N Duncan, J Eloff, V Naidoo
Ant. Tartrate30C once a day for 3 daysK. Glos 2015
Drosera rotundfolia30C once a day for 3 daysK. Glos 2015
Surgery

Prevention

  • Minimizing use of antibiotics and corticosteroids
  • Ensure coops are designed with good ventilation, to ensure regular air flow, with or without an open window.
  • Do not overcrowd birds
  • Remove any leftover uneaten feed and/or decaying vegetable or fruit matter daily
  • Do not expose birds to moldy straw or hay
  • Frequently move feeders and water dispensers to different areas to prevent fertile areas for growth of mold
  • Conduct regular air quality tests
  • Clean any mold present off hard surfaces with water and detergent, and dry completely. Absorbent materials such as ceiling tiles, that are moldy, should be replaced.
  • Reduce the potential for condensation on cold surfaces by adding insulation.

Prognosis

Treatment is usually long-term, frustrating, and often unrewarding if the disease is not recognized until the later stages of the infection. Early treatment is essential for a postive outcome.

Scientific References

Good Overviews

Risk Factors

  • Exposure to old, damp, or moldy bedding
  • Repeated or prolonged use of antibiotics
  • Steroid use, even for a short period of time
  • Weakened immune system
  • Shipping or relocating birds
  • Poor sanitation, leading to accumulation of old, moist food or droppings in bedding
  • Stress
  • Housing birds in confined areas with poor air flow
  • Winter season

Seasonality

WinterSpringSummerAutumn