Prevalence of megabacteria in budgerigar colonies

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.

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.

Changes in gut bacterial communities in canaries infected by Macrorhabdus ornithogaster

Macrorhabdus ornithogaster is an opportunistic yeast that colonizes the gastric mucosa of many avian species. Until now, no studies have focused on the influence of a gastric infection on the balance of the intestinal microbiota of birds. In this study, 44 faecal samples from individual canaries, with and without M. ornithogaster infection, were analysed. The detection of the yeast was evaluated by 18S rRNA PCR. In order to evaluate the impact of the Macrorhabdus infection on the bacterial communities, culture-independent methods, by the use of amplicon-based sequencing as well as 16S rRNA-DGGE, were adopted. The different health status of animals affected the relative abundance of the main OTUs, with a greater diversification of the gut microbiota in healthy animals compared to the infected. In particular, Lactococcus, Pseudomonas, Acinetobacter, Lachnospiraceae, Propionibacterium and Weissella were found to be characteristic of uninfected animals (FDR < 0.05), while Lactobacillus and Candidatus Arthromitus were characteristic of infected animals (FDR < 0.05). Both these taxa have been reported as immunostimulatory, involved in immunological disorders. In infected animals the inferred metagenome assessed by PICRUST clearly showed a positive correlation between the presence of M. ornithogaster and KEGG genes related to ether lipid metabolism, already reported to be immunostimulatory by activation of macrophages and to play a pathophysiological role in several immunological disorders. Finally, our results show an interaction between infection of the digestive tract and intestinal microbiota of pet birds and provide insight into the changing of the complex enteric bacterial community. HIGHLIGHTS Macrorabdus ornithogaster is a gastric yeast that colonizes a wide range of birds. Differences were found between infected and healthy animals in gut microbiota. Candidatus Arthromitus was closely associated with infected birds. M. ornithogaster can affect intestinal microbiota composition of canaries.

Comparison of Two Methods for Determining Prevalence of Macrorhabdus ornithogaster in a Flock of Captive Budgerigars (Melopsittacus undulatus)

Macrorhabdus ornithogaster is a yeast organism that infects multiple species of captive and wild birds. Diagnosis of infection in vivo has proven difficult historically, as shedding can be intermittent, and not all positive animals are clinically ill. We compared polymerase chain reaction (PCR) of cloacal swab samples and fecal Gram's stain (FGS) for diagnosis of active shedding of M ornithogaster in a captive flock of budgerigars ( Melopsittacus undulatus ). Of the 100 birds sampled, 57 (57%) were positive for M ornithogaster by PCR and 24 (24%) were positive for M ornithogaster by FGS. All FGS-tested birds also were positive on PCR. There was a significant association between the two methods, but the overall percent agreement for the two methods was only 67%. Based on these findings, cloacal swab PCR is more likely to diagnose the presence of M ornithogaster than FGS in budgerigars.

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.

The anatomy, physiology, and diseases of the avian proventriculus and ventriculus

Diseases affecting the proventriculus and ventriculus often present with similar clinical signs. It is important for the avian practitioner to be familiar with these diseases, their prevalence, and the species most commonly affected to judiciously prioritize the appropriate diagnostic techniques. A basic understanding of the anatomy and physiology of the proventriculus and ventriculus is useful in integrating the pathophysiology and clinical signs associated with variable disease processes. It is also essential to evaluate radiographs and endoscopic images, perform diagnostic techniques, make a diagnosis, and provide appropriate therapy.