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Aspergillosis

Bronchomycosis, Pneumomycosis

Aspergillosis is an opportunistic, noncontagious fungal infection caused by
inhalation of spores of ubiquitous, saprophytic fungi of the genus Aspergillus. The three most common species of this genus are A. fumigatus and A. niger, which cause aspergillosis, and A. flavus, which produces a mycotoxin (aflatoxin).

The disease usually affects the respiratory tract, but infections also can occur in the skin, bone, eye, gastrointestinal tract, and central nervous system. Aspergillosis is most often seen in chickens with poor immune systems and/or exposed to moldy or dusty environments with poor ventilation.

What are the symptoms of Aspergillosis?


Clinical signs associated with aspergillosis are somewhat nonspecific, and differ depending on the form, health of the chicken, and which organs are involved.
  • Acute form: This form of the disease occurs very rapidly and is believed to be caused by exposure to an overwhelming number of Aspergillus conidia. This form is most often seen in young chicks. Most affected birds will die within a few days without emergency veterinary care. The most common symptoms include:
    • Dyspnea
    • Gasping
    • Tail bobbing
    • Open mouth breathing
    • Sudden depression
    • Loss of appetite
    • Crop stasis
    • Vomiting
    • Cyanosis (bluish/purplish comb)
  • Chronic form: This form of the disease has a much more subtle onset, taking several weeks to 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 most common clinical symptoms observed include:
    • Lethargy
    • Change or loss of voice, often more apparent in roosters by lack or change in crow sounds.
    • Weight loss
    • Cough
    • Open mouth breathing
    • Cyanosis (blue/purple comb/wattles)
    • Depression
    • Vomiting
    • Decreased appetite
  • Disseminated aspergillosis: This form of the disease occurs when there are encephalitic and meningoencephalitic lesions in the brain involved. Clinical signs often consist of:
    • Weakness
    • Ataxia
    • Paralysis
    • Torticollis (wry neck)
    • Repeated falling on side or back
    • Difficulty moving
    • Tremors
    • Depression
    • Wing drooping
    • Unsteady gait
  • Mycotic keratitis: Occurs when infection occurs in the eye. Most common clinical signs include:
    • Sticky, swollen eyelids
    • Eye swelling
    • Eye discharge
    • Blepharospasm (eyelid spasm)
    • Sensitivity to light
    • Cloudy cornea
    • Cheesy yellow exudates within the conjunctival sac

What are the risk factors?


Stress and subsequent immunosupression are thought to play a key role in onset of the disease.
  • Pre-existing disease or chronic injury.
  • Exposure to damp feed, droppings, and bedding
  • 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. Overcrowding is stressful. Example stress 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

How is Aspergillosis diagnosed?


Early diagnosis and treatment of Aspergillosis can be difficult since obvious clinical signs often do not develop until the disease is advanced. Diagnostics include a complete blood count (CBC), biochemistry panel, aspergillosis antigen and antibody levels, protein electrophoresis, radiography and/or endoscopy, and fungal culture. A presumptive diagnosis of aspergillosis can usually be made based on the bird's history, clinical signs, physical exam and complete blood count (CBC).
  • CBC - May show an increase in white blood cell count with monocytosis during later stages of the disease.
  • Radiographs - May be helpful for finding general cloudiness to air sac or lung fields, and pulmonary or air sac granulomas. Although, these lesions will only be seen during the later stages of the infection.
  • Fungal culture - May be taken of the trachea, air sacs, or throat.

How is Aspergillosis treated?


Aspergillosis treatment is difficult and lengthy. Therapy generally consists of 4 to 6 months of systemic antifungal agents, such as itraconazole, topical application of antifungal agents to granulomas using endoscopy, or nebulization with antifungal agents. It also requires modification of the bird's environment, and supportive care.

Clinical Signs

Loss or change in voice
Exercise intolerance
Difficulty breathing
Tail bobbing
Abnormal crackles or clicking noises
Increased thirst
Reduced appetite
Weight loss
Lethargy
Increased time spent laying down
Isolation from flock members
Cough
Cyanosis
Open mouth breathing
Vomiting
Depression
Crop stasis
Gasping
Ataxia
Unsteady gait
Weakness
Paralysis
Wing drooping
Falling on the side or back
Tremors
Wheezing sounds
Swelling around the eye
Sensitive to light

Diagnosis

  • History
  • Clinical signs
  • Physical exam
  • Complete blood count (CBC)
  • Fungal culture - taken of the throat, trachea or air sacs
  • Cytology
  • Endoscopy
  • Radiography
  • 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.
Itraconazole5-10 mg/kg administered orally, twice a day
Amphotericin B1.5 mg/kg every 8 hours for 3-7 days (IV) or 1 mg/kg every 8 to 12 hours, diluted with 1 mL of sterile water (IT/nasal flush) or 7 mg/mL for 15 minutes of nebulization, every 12 hours.
Ketoconazole10-30 mg/kg administered orally every 12 hours for 21 days.
Voriconazole10 mg/kg every 12 hours, administered orally.
Terbinafine15-30 mg/kg administered orally, every 12 hours. Can also be nebulized by taking 1 mg/mL of solution and combining with itraconazole.
Clotimazole1% solution used for nasal flush or nebulization for 30-60 minutes.
Modification of environment.

Support

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.
  • 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 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

  • Living in an unsanitary, warm and humid environment with poor ventilation
  • Birds with an underlying illness or recovering from one in which their immune system is depressed.
  • Exposure to caked, moldy bedding (especially hay or straw)
  • Using corncob or walnut shells as bedding
  • Exposure to eucalyptus leaves
  • Improperly stored poultry feed

Seasonality

WinterSpringSummerAutumn