Chapter 169 Avian Infectious Diseases
ASPERGILLOSIS
• The acute form, which is seen most often in wild birds or psittacine birds under poor sanitary conditions, occurs after inhalation of an overwhelming number of spores. Severe dyspnea may result, with rapid progression to death.
• The chronic form, seen most often in psittacines, usually follows a stressful event or immunosuppressed state. Signs are often nonspecific and depend on the location of the infection and the immune status of the bird.
• The most common species isolated is Aspergillus fumigatus. A. flavus, A. niger, and other species play a lesser role.
Etiology
Predisposing factors include the following:
• Stress, as may occur in shipping, quarantine, or movement to an unfamiliar environment. Stress also may result from a prolonged illness, such as chlamydiosis, or after a traumatic event, such as an injury or smoke inhalation.
• Malnutrition or vitamin deficiencies, especially hypovitaminosis A, often occur in birds on diets consisting of seed only.
• Prolonged antibiotic or corticosteroid use may cause underlying immunosuppression. For example, aspergillosis may occur after treatment for chlamydiosis owing to the immunosuppressive effects of tetracycline in conjunction with the debilitated state of a diseased bird.
Clinical Signs
Chronic Form
The onset is insidious, and signs vary depending on the location of the infection.
Respiratory System
Upper Respiratory Tract Signs
• Signs include a change in voice, reluctance to talk, and a respiratory click that can be heard when lesions involve the main airways, especially the syrinx.
• Severe, life-threatening dyspnea often occurs if the lesions are large enough to occlude the trachea or syrinx. In some cases, these may be the only lesions present.
• Erosion of the nasal conchae and misshapened nares are seen in advanced cases of nasal aspergillosis.
Lower Respiratory Tract Signs
• With mild to moderate aspergillus airsacculitis, the air sacs are usually able to function normally (i.e., inflate and deflate to move air through the lungs). In these birds, respiratory signs are mild or absent, especially in birds that are sedentary.
• Dyspnea or exercise intolerance is seen in birds with extensive pneumonia or air sac involvement. Air sacs may become thickened or filled with caseous exudate, inhibiting their ability to move air.
• Respiratory signs are more likely to occur earlier in birds that are permitted to fly, as oxygen demand is greater in these birds.
Diagnosis
Physical Examination
• Examine the mouth and nares for mucus, exudates, or deformation of the nares. Take samples from the trachea or choana for fungal culture.
Laboratory Tests
• A severe leukocytosis often ranging from 25,000 to 100,000 white blood cells (WBCs) per microliter is often present.
• The differential count usually reveals heterophilia, monocytosis, lymphopenia, and anemia of chronic disease. Occasionally, the complete blood count (CBC) is normal.
• Increased serum total protein with an increased beta or gamma globulin portion is seen on plasma protein electrophoresis (EPH) in birds with chronic disease.
Endoscopy
• When there are episodes of severe dyspnea, tracheal endoscopy may reveal a single lesion occluding the syrinx.
• If a thick, white discharge or plaque is seen in the trachea, obtain a sample for cytologic examination and culture on Sabouraud’s dextrose agar.
• Endoscopy of the abdominal air sacs may reveal diffuse cloudiness or white to yellow plaques. These plaques may become covered with a green-gray pigmented mold; obtain samples for culture and cytology.
Radiography
• Radiographs are generally not sensitive for defining tracheal granulomas, although if a soft tissue mass is seen within the trachea, aspergillosis should be suspected.
• In birds with nasal or sinus aspergillosis, perform cranial imaging such as skull radiographs, computed tomography (CT), or magnetic resonance imaging (MRI) to assess for the presence of granulomatous or caseated masses. Skull radiographs are less sensitive for picking up small lesions but are more readily available than CT or MRI.
• In advanced disease, radiographic abnormalities can include loss of definition of the air sacs, asymmetry of the air sacs due to air sac collapse or hyperinflation, and focal densities in the lungs or air sacs.
Treatment
Antifungal Agents
• For birds with severe infections, administer amphotericin B (Fungizone, Squibb), 1.5 mg/kg q8h IV, for 3 to 7 days. Mask the bird with isoflurane anesthesia, and maintain an IV catheter for each injection.
• In birds with syringeal lesions, administer amphotericin B by intratracheal injection, using a tomcat urinary catheter (Sherwood Medical) at a dosage of 1 mg/kg q12h for up to 1 month.
• For nasal aspergillosis, a solution of 0.05 mg of amphotericin B per milliliter of sterile water may be used to flush the nares.
• For mycotic airsacculitis, make a solution of 1 mg of amphotericin B per milliliter of sterile water and nebulize q12h for 15 minutes. Alternatively, nebulize with clotrimazole (10 mg/ml in polyethylene glycol).
• Amphotericin B is potentially nephrotoxic and may cause bone marrow suppression. Monitor serum uric acid concentration to detect toxicity.
• Administer itraconazole (Sporanox, Janssen), 10 mg/kg q12h (with food) alone, in conjunction with, or following amphotericin B treatment. Usually at least 6 to 8 weeks of treatment are necessary; some birds may require treatment for months. Obtain a plasma biochemistry profile every 2 to 4 weeks to monitor for hepatotoxicity during treatment. African grey parrots appear to be more sensitive to the hepatotoxic effects of itraconazole. Use with caution, and discontinue use if anorexia occurs.
• Alternatively, administer fluconazole (Diflucan, Roerig), 15 mg/kg q24h PO, for up to 6 weeks with or after amphotericin B. Fluconazole is usually not as effective as itraconazole, but it may be better tolerated by some species, especially African grey parrots.
• Terbinafine (Lamisil, Novartis), 10 mg/kg q12h, PO has been anecdotally used to successfully treat aspergillosis in birds.
• 5-Fluorocytosine (Ancobon, Roche Labs), 50 to 150 mg/kg q12h PO, in conjunction with or after amphotericin B treatment has been used to treat aspergillosis in raptors. Give the higher dosage for active infections; use the lower dosage, often prophylactically, for 10 to 14 days in high-risk patients.
Surgical Treatment
• Surgical removal of large accumulations of caseous material from air sacs in conjunction with systemic treatment and nebulization is often necessary for successful treatment.
Supportive Care
• Fluid therapy, forced alimentation (see Chapter 168), and a warm environment are required for debilitated birds.
CHLAMYDIOSIS
Etiology
Chlamydiosis is potentially zoonotic and a reportable disease in many states. A valuable resource for practicing veterinarians, the compendium of psittacosis control is updated yearly by the Association of Public Health Veterinarians and is available at www.avma.org/.
Life Cycle and Transmission
Chlamydophila have a biphasic life cycle.
• Infectious, extracellular elementary bodies are shed in oral or nasal secretions and feces and may survive outside the host for a month or longer. Dissemination may occur via shared food dishes or aerosolized fecal dust.
• Elementary bodies are inhaled or ingested and enter host cells, where they undergo cellular rearrangement to form reticulate bodies, the replicating form of the organism.
Clinical Signs
• Inapparent carriers are common. These may be birds that have recovered from clinical illness or that may have never shown signs. High numbers of organisms may be shed intermittently from the feces or nasal or oral secretions, putting other pet birds and humans at risk.
• Clinical signs may develop in these carriers when they are stressed or otherwise immunocompromised.
Acute Form
• The acute form of the disease is seen more often in young or immunosuppressed birds. Signs may include the following:
• Liver or gastrointestinal (GI) signs, such as inappetence, green-gray diarrhea, biliverdinuria (lime-green urates), and occasionally vomiting or regurgitation
• Respiratory signs, including serous to purulent nasal or ocular discharge, labored breathing, blepharitis, and conjunctivitis
Diagnosis
History
• Recently acquired birds may be at higher risk because of the increased exposure and stress associated with transport.
Physical Examination
• Suspect chlamydiosis in birds with poor feathering, weight loss, or signs of GI or respiratory disease.
Laboratory Tests
• Leukocytosis, often >40,000 WBC per microliter demonstrating heterophilia with toxic heterophils, usually is seen in acute disease. Relative monocytosis and reactive lymphocytes and basophilia are often present.
• Serum protein usually is elevated as a result of chronic inflammatory stimulation. Plasma protein electrophoresis may demonstrate hypergammaglobulinemia and hypoalbuminemia.
Antigen Capture
Immunoassay
• An immunoassay (IDEIA antigen system, California Avian Laboratories, Citrus Heights, CA) may be used to detect chlamydial antigen in naso-ocular discharges, pharyngeal swabs, and feces. The chlamydial organisms do not have to be viable for antigen to be detected.
• Shedding is inhibited temporarily in birds tested within 1 to 2 weeks of treatment with erythromycin (e.g., Ornacyn, available in pet stores), doxycycline, tetracyclines, penicillins, chloramphenicol, tylosin, and quinolones.
Serology
Complement Fixation
• In the complement fixation (CF) test (Texas Veterinary Medical Diagnostic Laboratory, College Station, TX), single serum samples are of value if the titer is sufficiently high.
• Titers up to 1:8 are considered negative, 1:16 to 1:32 is suspicious, and >1:64 is positive. A fourfold rise in titer over a 4-week period is considered most significant. Titers may remain high following successful treatment.
• Young birds, budgerigars, cockatiels, canaries, and finches with chlamydiosis may not produce antibody titers high enough to be detectable by CF, making negative results unreliable in these birds.
DNA Probe
• A highly sensitive and specific DNA probe for the detection of Chlamydophila infection is commercially available. Samples may be taken from blood, the oropharynx or cloaca.
• For Chlamydophila organisms to be detected in oropharyngeal secretions or cloacal swabs, the bird must be actively shedding organisms. Therefore, false-negative results are possible. However, a DNA probe is significantly more sensitive for detecting shedding than any other available method.
• For Chlamydophila organisms to be detected in blood samples, the bird must be bacteremic. Therefore, false-negative results are possible.
Isolation on Culture
• Success is highly dependent on proper transport medium, transport conditions, and previous antibiotic treatment.
• The chlamydial agent may be propagated in tissue culture, mice, or embryonated chicken eggs. Obtain postmortem samples from the spleen, liver, or air sacs.
• Isolation may be possible from antemortem exudate or fecal samples; however, shedding often is intermittent. This is the most reliable postmortem confirmation.
Treatment
Tetracyclines are the most effective antibiotics against Chlamydophila.
• Doxycycline (Vibramycin, Pfizer) is the drug of choice for treatment of Chlamydophila. It is available in an oral (suspension, solution, or capsules) or IV form in the United States. The IV form should not be injected IM or SC.
• The dosage of doxycycline varies, depending on the species. Administer 25 mg/kg q24h to macaws and cockatoos and 35 to 50 mg/kg q24h to African grey parrots, cockatiels, and Amazon parrots. Senegal parrots require 30 mg/kg q12h. Some birds will regurgitate on higher doses. Doxycycline may be mixed with a small amount of a favorite food, as long as that food is immediately and completely consumed.
• For cockatiels and budgerigars, doxycycline may be added to a mixture of hulled millet seed and oats. Lightly coat the seed-oat mixture with sunflower oil, and add doxycycline at a rate of 300 mg/kg of seed mix. Feed birds this mix exclusively for 45 days. Use this route only in stable birds. Monitor birds to ensure that they are eating this diet.
• Doxycycline for IM injection (Vibravenos, Pfizer) is available in countries outside of the United States and may be imported for use in birds. Administer 75 to 100 mg/kg IM every 7 days for 6 weeks.
• Doxycycline may be effective for some birds when added to the drinking water. Use this route only in stable birds, and carefully monitor the birds to ensure that the water is palatable and that water consumption is normal. Birds may overconsume water during hot, dry periods or while on dry or pelleted diets, resulting in overdosage. Underdosage, resulting in treatment failures and possibly dehydration, may occur if birds refuse to drink treated water. Species that normally consume very little water, such as budgerigars cannot be effectively treated using water-based medication. Dosages are available for a limited number of species and include 300 to 400 mg/L water for cockatiels, 400 mg/L water for Goffin’s cockatoos, and 600 to 800 mg/L water for African grey parrots.
• Secondary mycotic or bacterial infections owing to alterations of the normal enteric flora, stress, and immunosuppression are a common problem in birds treated with doxycycline.
• Thoroughly clean the environment following treatment to remove chlamydia organisms and prevent reinfection.
Prevention
• Because inapparent carriers are common and an accurate screening test is not available, it is difficult to prevent the introduction of Chlamydia organisms into a flock when purchasing new birds. A combination of serology and DNA probe to screen for chlamydiosis is recommended, with repeated yearly testing.
