THE MERCK VETERINARY MANUAL
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Bacterial Diseases of Pet Birds

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The gram-negative bacteria of the family Enterobacteriaceae are common avian pathogens, although many are regarded as opportunists. Escherichia coli, Pseudomonas, Aeromonas, Serratia marcescens, Salmonella, Klebsiella, Enterobacter, Proteus, and Citrobacter spp are frequently isolated.

Salmonellosis is not often reported but may produce clinical disease in birds that are immunocompromised or stressed.

Pasteurella spp have been reported as possible septicemic agents in birds attacked by pet cats or rats.

Mycoplasma spp have been implicated in the chronic sinusitis often found in cockatiels. This organism is difficult to culture, and the true incidence is unknown.

Avian tuberculosis is a common problem in the gray-cheeked parakeet and other Brotogeris spp, in addition to affecting a wide variety of other avian species in collections.

Mycobacterium avium, M intracellulare, and M genavense are the 3 species most frequently linked to pet bird mycobacteriosis. The most commonly affected organs in pet birds are the GI tract, liver, and spleen.

Staphylococci and streptococci (especially hemolytic strains) and Bacillus spp are thought to be responsible for several dermatologic conditions in psittacines. Staphylococci are often isolated from lesions of pododermatitis (bumblefoot) in many avian species. As in many other species, methicillin-resistant Staphylococcus aureus are being isolated from birds with increasing frequency.

Clostridial organisms are common secondary invaders of damaged cloacal tissue in birds with cloacal prolapse or papillomatosis. Several specific syndromes of birds can arise from various species of Clostridia. A Gram's stain or other direct cytologic examination is necessary to identify these organisms, as aerobic cultures in these cases prove negative or identify bacteria that are not significant. If a Gram's stain reveals organisms suspected to be Clostridia, an anaerobic culture can be performed to speciate the bacteria.

see Antimicrobials Used in Pet BirdsTables for a partial list of antimicrobials frequently recommended for caged birds.

Table 2

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Chlamydiosis

(Psittacosis, Ornithosis)

Chlamydia psittaci has been reclassified as Chlamydophila psittaci. Several parameters of this organism have been reexamined, including incubation, necessary duration of treatment, and degree of zoonotic potential. Current state and federal regulations governing the testing, reporting, treatment, and quarantine for Chlamydophila should be followed.

Clinical presentations of Chlamydophila in psittacine birds vary. Nonspecific signs may include ocular, nasal, or conjunctival irritation and discharge; anorexia; dyspnea; depression; dehydration; polyuria; biliverdinuria; and diarrhea.

Various antibody and antigen tests are available, but these have limitations. Due to the intracellular nature of Chlamydophila, and the reduction in numbers that accompanies antibiotic use, false-negative antigen tests are common. Acutely ill birds may not mount an antibody response, also yielding false-negative results. Lastly, exposed but clinically normal birds may produce appreciable antibody titers. These factors make an antibody test an insufficient screening tool for chlamydiosis in birds when used alone. With the advent of PCR testing, diagnosis of Chlamydophila is more readily accomplished. Attempts to culture the organism or identify elementary bodies in tissue specimens are less often performed. Laboratories should be consulted prior to shipment to identify appropriate samples and shipping methods.

Doxycycline is commonly used for treatment of Chlamydophila infection. Formulations of doxycycline in the seed and water and chlortetracycline-impregnated seeds or other foods are available or can be manufactured for treatment of affected flocks. A doxycycline medicated feed for budgerigars can be created by combining 300 mg of doxycycline hyclate (from capsules) with 1 kg of a mixture of oats, millet, and sunflower oil. (1 part cracked steel oats is mixed with 3 parts hulled millet; add 5–6 mL of sunflower oil per kg of the oat/seed mixture.) Fresh medicated mix should be made daily and fed as the sole diet for 30 days. Doxycycline may also be added to the water for cockatiels (200–400 mg doxycycline hyclate/L of water), Goffin's cockatoos (400–600 mg/L), and African Grey parrots (800 mg/L). A doxycycline syrup, using a monohydrate- or calcium-syrup formulation, can be given at 40–50 mg/kg, PO, sid to cockatiels, Senegal parrots, and blue-fronted and orange-winged Amazon parrots; in African Grey parrots, Goffin's cockatoos, blue and gold macaws, and green-winged macaws, the recommended dosage is 25 mg/kg, PO, sid. These indirect modes of antibiotic administration depend on ingestion of sufficient quantities of antibiotics to maintain effective blood levels, which may not always occur.

Last full review/revision July 2011 by Teresa L. Lightfoot, DVM, DABVP (Avian)

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