Megabacteriosis in budgerigars: diagnosis and treatment

Verification of accuracy of qPCR method for intravital diagnostics of Macrorhabdus ornithogaster in avian droppings

The objective of this study was to verify the accuracy of the quantitative PCR (qPCR) method for in vivo detection of Macrorhabdus ornithogaster. A total of 100 faecal and gastric mucosa samples from avian cadavers were investigated, using cytological and qPCR techniques (budgerigars, Fischer's lovebirds, red-crowned parakeets, scarlet-chested parrots, eastern rosellas, domestic canaries, zebra finches, white Java sparrow). Using qPCR, the probability of detecting positive samples of droppings was significantly higher than in the faecal smear microscopy (P < 0.01). Cytology detected the presence of Macrorhabdus ornithogaster in 34 faecal samples, whereas qPCR detected 54 positive samples. In all 46 qPCR negative faecal samples, gastric smear qPCR was performed and also yielded negative results. Gastric smear qPCR was also performed in 20 cadavers where faecal qPCR has detected the presence of Macrorhabdus ornithogaster and in all samples confirmed the positive result. This verifies the accuracy of faecal sample qPCR for intravital diagnostics. Overall, the faecal qPCR technique appears to be extremely reliable, as it made it possible to detect all infected individuals, including those with negative stool or gastric cytology.

MORTALITY TRENDS FOR BUDGERIGARS (MELOPSITTACUS UNDULATUS) HOUSED IN A WALK-THROUGH AVIARY IN A ZOO IN NORTH AMERICA, 2009-2019

Many zoos in North America feature walk-through exhibits that allow members of the public to interact with psittacine species, as these exhibits are popular with guests and can generate additional revenue. There is limited research available on the life expectancy and common causes of mortality of psittacines when group-housed in aviaries. This study compiled data on 496 budgerigar (Melopsittacus undulatus) mortalities at a walk-through aviary at a North American zoo from March 2009 to March 2019, including histopathology on 62 tissue sets collected post mortem, and gross necropsy data for 163 birds deceased from March 2015 to March 2019. The mean age at death or euthanasia of all fledged birds from 2015 to 2019 was 3.57 ± 1.58 yr. The most common causes of death or euthanasia found on gross necropsy were granulomatous disease (39.2%), trauma (16.0%), and Macrorhabdus ornithogaster (13.5%). The most common histologic finding was M. ornithogaster, described as the primary pathologic finding in 31.7% of submitted tissue sets, and recorded as a secondary pathologic finding in 53.2% of submitted tissue sets. Mycobacterial disease was the primary pathologic finding in 25.3% of submitted tissue sets, and was recorded as an additional pathologic finding in 35.4% of submitted tissue sets.

Therapeutics in Herd/Flock Medicine

When treatment is required for a herd/flock health concern, a range of factors must be considered to determine the preferred treatment strategy. If a group treatment strategy is pursued, considerations to optimize the likelihood of safe and effective group treatment include taxon-specific pharmacokinetics/pharmacodynamics, the formulation of prescribed medication, the type and amount of food, the number and type of water sources, enclosure design, size and demography of the group, weather conditions, and health status of individuals in the group. In addition, antimicrobial stewardship principles and relevant legislation/regulation must be at the forefront of decision making.

Avian Gastric Yeast (Macrorhabdus ornithogaster) and Mycobacterium genavense Infections in a Zoo Budgerigar (Melopsittacus undulatus) Flock

Over a 4-mo period, a Michigan zoo had 32 budgerigars, Melopsittacus undulatus, from their flock die. Whole animals or formalin-fixed tissues were submitted to Michigan State University Veterinary Diagnostic Laboratory for diagnosis. Avian gastric yeast infection, Macrorhabdus ornithogaster, was diagnosed in seven birds. There was atrophy of breast musculature and no subcutaneous or coelomic fat stores in six necropsied birds. Only two birds had proventricular dilatation grossly. Histologic examination of the proventriculus of all seven birds revealed abundant 3 × 50-µm septate, parallel-walled, nonbranching yeast organisms morphologically consistent with Macrorhabdus ornithogaster. Mycobacteriosis was diagnosed in three budgerigars, two of which were necropsied. Both necropsied birds had hepatomegaly and one also had splenomegaly. No acid-fast bacilli were found in the livers of either bird but were found in splenic macrophages of the bird with splenomegaly and in the intestine of the other bird. Mycobacterium species were cultured from the enlarged spleen and identified by DNA sequence as Mycobacterium genavense. Pulmonary granulomas with acid-fast bacilli were found in the bird submitted as fixed tissues. None of the budgerigars had a dual infection. The remainder of the budgerigars died from hepatitis, nephrosis, oviductal prolapse, exclusion from food and water by flock mates, or tumors.

Comparison of Two Treatment Modalities and PCR to Assess Treatment Effectiveness in Macrorhabdosis

Macrorhabdosis is a debilitating disease condition that affects budgerigars (Melopsittacus undulatus), cockatiels (Nymphicus hollandicus), and many other bird species worldwide. Macrorhabdus ornithogaster is a pathogen which leads to nonspecific clinical signs, and to date, diagnosis as well as therapy are still challenging. In this study, medical histories of 32 budgerigars and 7 cockatiels with macrorhabdosis diagnosed clinically and by polymerase chain reaction (PCR) within a period of 24 months (from January 2016 to January 2018) were retrospectively analyzed. Macrorhabdus ornithogaster was diagnosed through fecal samples collected over several days and analyzed by microscopic examination or PCR. The effectiveness of 2 different amphotericin B treatment regimens were investigated by PCR. In 23 cases, treatment was performed with amphotericin B via drinking water at 0.1 mg/mL for 28 days. For the remaining 16 birds, an alternative treatment regimen of amphotericin B at 100 mg/kg PO q12h for 10 days was combined with administration of amphotericin B via drinking water at 0.1 mg/mL for 28 days. Fecal samples of all treated flocks were reexamined by PCR 10-14 days post-amphotericin B treatment. More than half (56.4%) of the treated birds tested negative for M ornithogaster irrespective of the treatment regimen. In addition to clinical improvement and microscopic examination of droppings, PCR was used for the first time to evaluate treatment response in birds diagnosed with M ornithogaster. Administration of amphotericin B via drinking water proved to be effective in more than 50% of cases, indicating a less stressful alternative to the oral administration of amphotericin B twice daily.

Avian gastric yeast (AGY) infection (macrorhabdiosis or megabacteriosis)

The review on avian gastric yeast (AGY) aimed to collect and update available information about this infection from clinical point of view which can help for better understanding of the disease. Macrorhabdus ornithogaster (M. ornithogaster) is the causative agent of proventriculitis in birds. The orga­nism is large, rod-like, classified as anamorphic ascomycetous yeast. Clinical signs may vary from acute with sudden death or chronic wasting. Diarrhoea or enteritis has also been reported in infected birds. Birds can have other concurrent infections (enteric parasites, bacteria or viruses). Gross lesions may include proventricular oedema, hyperaemia, or haemorrhage, with overproduction of mucus accumulated in the proventricular lumen. The proventriculus may be dilated with or without ulceration in mucosa. The organism can be cultured on De Man, Rogosa and Sharpe (MRS) agar, but it is easily detected in Gram’s, periodic acid-Schiff (PAS) and Giemsa stained proventricular/ventricular junction, or isthmus sections. Histological changes are more prominent in the ventriculus. Affected birds have marked disruption of the koilin layer with disorganisation and degeneration, and demonstrate large numbers of yeasts with matchstick or logjam appearance. The organism can be detected by polymerase chain reaction (PCR). The disease is common in budgerigars, canaries, finches, and parrotlets. Organisms are identified retrospectively in approximately one-fourth of canaries and bud­ge­rigars. The infection has also been reported in chickens, partridges, and ostriches but mildly in chickens. The affected birds can be successfully treated with amphotericin B.

Macrorhabdus ornithogaster Infection and Spontaneous Proventricular Adenocarcinoma in Budgerigars ( Melopsittacus undulatus)

Proventricular infection with the anamorphic, ascomycetous yeast Macrorhabdus ornithogaster and disease associated with infection (macrorhabdiosis) have been widely reported in budgerigars ( Melopsittacus undulatus). Proventricular adenocarcinoma has also been previously reported in this species. In a retrospective archival search of clinical cases submitted to a zoo animal and exotic pet pathology service between 1998 and 2013, a total of 28 128 avian submissions were identified, which included 1006 budgerigars kept in zoos or aviaries or as pets. Of these budgerigars, 177 were identified histologically as infected with M. orthithogaster at the time of necropsy. Histologic examination of tissues from budgerigars infected with M. orthithogaster identified an apparent continuum in the development of proventricular isthmus lesions associated with M. ornithogaster that included inflammation, mucosal hyperplasia, glandular dysplasia, and adenocarcinoma. Proventricular adenocarcinoma was identified histologically in 21 budgerigars. Budgerigars with proventricular adenocarcinoma were significantly more likely to have macrorhabdiosis than budgerigars without proventricular adenocarcinoma. Based on odds ratios for archival data, budgerigars were 41 times (95% confidence interval [CI], 33-52) more likely to have macrorhabdiosis than other avian species and 19 times (95% CI, 11-33) more likely to have proventricular adenocarcinoma than other birds. Budgerigars were 323 times (95% CI, 42-2490) more likely to be affected by both diseases simultaneously compared with other avian species. These findings suggest that macrorhabdiosis may be an associated factor for proventricular adenocarcinoma, although the explanation for this statistically significant correlation remains unknown and further investigation is warranted.

Antifungal Therapy in Birds: Old Drugs in a New Jacket

The use of antifungals in birds is characterized by interspecies and interindividual variability in the pharmacokinetics, affecting drug safety and efficacy. Oral antifungal drug absorption is a complex process affected by drug formulation characteristics, gastrointestinal anatomy, and physiology. New antifungal drug delivery systems can enhance drug stability, reduce off-target side effects, prolong residence time in the blood, and improve efficacy. Topical administration of antifungals through nebulization shows promising results. However, therapeutic output is highly influenced by drug formulation and type of nebulizer, indicating these factors should be taken into account when selecting this medication route.

Update on the diagnosis and management of Macrorhabdus ornithogaster (formerly megabacteria) in avian patients

Macrorhabdus ornithogaster, a yeast found only at the junction between the ventriculus and proventriculus, can infect a wide range of birds. Infection is often subclinical but can also result in gastrointestinal signs. Direct observation of the organism in the feces is a specific but somewhat insensitive means of diagnosis. At least three antifungal drugs are reported to be effective for treatment but resistance to one or more of these drugs may occur.