Investigation of the diagnosis and treatment of Macrorhabdus ornithogaster in Budgerigars (Melopsittacus undulatus)

Macrorhabdus ornithogaster (MO) is a pathogenic yeast that can cause significant morbidity and mortality in both wild and captive birds. Budgerigars (Melopsittacus undulatus) are a commonly affected species, making this an important disease of client-owned birds and zoological collections. Antemortem diagnosis is difficult given variable shedding, lack of available diagnostic assays to quantify the pathogen, and inability to maintain this pathogen in any lab in the world. In addition, there is a lack of curative treatments for this pathogen. Given the broad avian taxonomic range in which this pathogen has been identified, the challenges with diagnosis, and inconsistent treatment results, we aimed to 1) develop a novel quantitative polymerase-chain reaction (qPCR) assay to quantify MO DNA from feces, 2) culture MO in vitro to test antifungal susceptibility, and 3) use the novel qPCR assay to assess the prevalence of MO in both wild and managed birds. A TaqMan qPCR assay targeting a 94 bp segment of MO 18S rRNA was developed and validated, performing with high efficiency (slope = -3.355, R2 = 0.999, efficiency = 98.622) and low intra- and inter-assay variability (coefficient of variation <2.63% at all dilutions). MO culture was successfully performed using proventricular-ventricular samples and feces from deceased, cytology-positive budgerigars using Basal Medium Eagle or chicken serum media, 20% fetal bovine serum, 5% sucrose, 100 units/mL penicillin, 100 µg/mL streptomycin, and 25 µg/mL chloramphenicol at pH 3-4 and 42°C under microaerophilic conditions. MO was successfully cultured from four different infected budgerigars using this culture protocol; however, cultures did not maintain long enough for antifungal susceptibility testing. Prevalence testing was performed using the novel qPCR, revealing an overall MO prevalence of 9.4% in a managed zoological budgerigar population, which was lower than in previous prevalence reports. No wild birds from northeastern Illinois tested positive for MO. Budgerigars that were positive for MO on qPCR had significantly lower weights than negative birds. These findings demonstrate the utility of a novel MO qPCR for antemortem diagnosis of MO in bird feces and the potential impact that MO presence has on the health of infected budgerigars. The low prevalence in this population prompts further investigation into improving diagnostic sensitivity for detecting this organism, especially with intermittent shedding.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

VMS-Veterinary Clinical Medcne

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Lang, Danielle Marie

Contributors dc:contributor

• Allender, Matthew C
• Delk, Katie W
• Langan, Jennifer N
• Chinnadurai, Sathya K

• Macrorhabdus ornithogaster
• budgerigar
• Melopsittacus undulatus

Statement dc:rights

• Copyright 2025 Danielle Lang

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129562

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129562