Chapter 169 Avian Infectious Diseases
Aspergillosis is an infectious but not contagious disease of pet and wild birds that is caused by the ubiquitous soil saprophyte Aspergillus. Infection generally occurs via inhalation of spores, resulting in primary lesions in the thoracic and abdominal air sacs and in the large airways (syrinx). Dissemination to other organ systems often occurs. Two forms of the disease, acute and chronic, commonly are seen.
Aspergillosis is an opportunistic disease, requiring predisposing immunosuppressive factors such as stress, malnutrition, and environmental factors.
Predisposing factors include the following:
The onset is insidious, and signs vary depending on the location of the infection.
Signs depend on the area affected. Respiratory signs will only occur if lesions impede airflow, for example, aspergillus granuloma formation in the syrinx, air sac thickening, and exudate accumulation in the air sacs.
Upper Respiratory Tract Signs
Lower Respiratory Tract Signs
Liver and Kidneys
Diarrhea, anorexia, and polyuria may be seen. Green discoloration of the urates (biliverdinuria) and hepatomegaly occasionally are seen.
Treatment is most successful with early lesions confined to the nares or syrinx and when aggressive treatment is instituted early. A combination of topical treatment such as tracheal injection, sinus flush or nebulization (depending on the site of infection), systemic treatment, and debridement are usually necessary for successful outcome. Treatment is prolonged, requiring weeks to months of outpatient therapy. Continue treatment until clinicopathologic changes normalize and radiographic and endoscopic lesions resolve.
Avian chlamydiosis is known as psittacosis when occurring in psittacine species and ornithosis when occurring in passerine species. The incidence in pet birds is high and is reportedly 15% to 30% of those tested.
Avian chlamydiosis is caused by the obligate intracellular bacteria Chlamydophila psittaci. The organism infects many species of wild, domestic, and exotic birds, domestic mammals, and humans. Manifestation of this disease varies from subclinical to fatal, depending on the strain of C. psittaci involved and the species of bird affected.
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.
Clinical signs vary greatly, depending on the organ system affected, virulence of the organism, and immune status of the host.
Elementary Body Agglutination (Texas Veterinary Medical Diagnostic Laboratory)
Isolation on Culture
False-negative results are common when testing for Chlamydophila organisms owing to intermittent shedding, administration of inhibitory antimicrobials, and production of low antibody titers in the face of active disease. Base the diagnosis of chlamydiosis on a combination of DNA probe and serologic testing, clinical signs, hematology, serum biochemical profile, plasma protein electrophoresis, and radiography.
Tetracyclines are the most effective antibiotics against Chlamydophila.
Tetracyclines must be administered for 45 days to be effective in eliminating infection. Client compliance is often a problem, especially when once- or twice-daily oral administration is prescribed. Treat clinically ill birds by a parenteral or direct oral route. Use food- and water-based dosage regimens in stable birds only. Monitor these birds to ensure that the treated food or water is being appropriately consumed.
PSITTACINE VIRAL DISEASES
Psittacine Circovirus: Psittacine Beak and Feather Disease
Psittacine beak and feather disease (PBFD) is an infectious, sometimes fatal disease characterized by feather loss, feather dystrophy, occasional beak deformity, and destruction of the thymus and bursa. Originally believed to affect only white and pink cockatoos and a few other South Pacific psittacine birds, the disease has been reported in more than 30 species of Asian and South Pacific psittacine birds and is believed to be capable of causing disease in many others. Occurrence in Central and South American psittacine birds is rare. Death is attributed to secondary bacterial, viral, or mycotic infections or to general debilitation.