Prolonged fecal shedding of ‘megabacteria’ (Macrorhabdus ornithogaster) by clinically healthy canaries (Serinus canaria)

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.

Comparison of In-Clinic Diagnostic Testing Methods for Macrorhabdus ornithogaster

Macrorhabdus ornithogaster is an ascomycete yeast often found at the isthmus of the ventriculus and proventriculus of infected birds. Antemortem diagnosis has traditionally involved direct visualization of organisms on wet-mount or gram-stained fecal preparations, cloacal and crop swabs, or by both methods; however, different in-clinic diagnostic techniques have never been compared to establish an optimum test for the identification of M ornithogaster in an avian patient. We compared 5 microscopically evaluated diagnostic testing methods: fecal Gram's stain, direct fecal wet preparation, macro suspension technique, macro suspension with Gram's stain, and macro suspension stained with new methylene blue. Each technique was performed on 96 fecal samples collected during the treatment of M ornithogaster-infected budgerigars with water-soluble amphotericin B. The macro suspension technique produced statistically higher organism counts than the other 4 techniques and was always estimated to have the largest detection probability. We recommend that the macro suspension technique be implemented as the most efficacious diagnostic test for in-clinic assessment of avian patients possibly infected with M ornithogaster.

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.

Inconsistent efficacy of water-soluble amphotericin B for the treatment of Macrorhabdus ornithogaster in a budgerigar (Melopsittacus undulatus) aviary

OBJECTIVE

To assess the efficacy of a commercially available in-water amphotericin B treatment for Macrorhabdus ornithogaster.

DESIGN

Clinical treatment trial.

METHODS

Faecal shedding of 16 naturally infected budgerigars (Melopsittacus undulatus) was monitored while they were being treated using in-water amphotericin B, as per the manufacturer's instructions, for 10 days. Any birds that remained positive after 10 days received a further 10 day course of treatment. All birds were rechecked 16 days after the end of the second treatment period.

RESULTS

At the conclusion of treatment, 11 birds had stopped shedding M. ornithogaster, and 5 birds were still shedding. Sixteen days after the conclusion of the second treatment period, four birds that were negative after 10 days of treatment were shedding again, and two of the birds that were treated for 20 days were shedding. In addition, one bird from each treatment group died after treatment and before follow-up testing.

CONCLUSION

These findings represent a 36% treatment failure, suggesting that treatment with the commercially available, water-soluble amphotericin B has inconsistent efficacy against M. ornithogaster in some budgerigars in Australia and is not effective for eliminating it from budgerigar aviaries.

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.

New Diagnostic Insights for Macrorhabdus ornithogaster Infection

The aim of this study was to propose the use of a new rapid and user-friendly diagnostic tool for the detection of Macrorhabdus ornithogaster infection in birds. The current report focuses on the diagnostic feasibility of different methods, with particular emphasis on the application of the mini-Flotac technique for the diagnosis of M. ornithogaster infection. The mini-Flotac method is particularly tailored for epidemiological monitoring and surveillance, where large numbers of fecal samples must be rapidly, yet reliably, examined. Gram staining, as the standard method, was used to validate the reliability of the mini-Flotac method. This tool has not yet been used in avian species or in the diagnosis of yeast infections. In our study, M. ornithogaster showed excellent performance in a flotation assay, which had not been demonstrated previously. Our results suggest that the mini-Flotac method is a valid, sensitive, and potentially low-cost alternative technique for use in the diagnosis of this yeast infection in birds.