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Prevalence of Avian Gastric Yeast (Macrorhabdus ornithogaster) in Parrots and Parakeets of Iran

Muhammad H Kafrashi , and Daryoush Babazadeh

Faculty of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad, Iran

Pet and Exotic Diseases Clinic, Aria Veterinary Hospital, Mashhad, Iran

Corresponding author: Daryoush Babazadeh, Pet and Exotic Diseases Clinic, Aria Veterinary Hospital, Mashhad, Iran. Email:


The avian gastric yeast (Macrorhabdus ornithogaster) is a microorganism that infects aviary birds worldwide and can cause chronic wasting disease. Macrorhabdus ornithogaster, previously named Megabacter, infects a large group of companion birds, such as cockatiels, budgerigars, lovebirds, parrots, African gray parrots, and greencheeked parakeets. The aim of the present study was to evaluate the prevalence of Macrorhabdus ornithogaster in some companion birds and to show their prospects in the future. A total of 145 companion birds, including 50 cockatiels, 20 gray parrots, 20 Budgerigars, 5 parrots, 30 love birds, and 20 green cheeks with symptoms, such as lethargy, weight loss, regurgitation, gasping and anorexia referred to the Aria Veterinary Hospital, Mashhad, Iran, during 2021-2022. The fecal samples were collected from all birds and were randomly evaluated for gastric yeast using direct smear and the gram-staining method. The results revealed that almost 73 percent of the symptomatic cases showed active or non-active yeasts in their microscope slides. A 14-day treatment of nystatin, apple vinegar, and metronidazole was applied for all cases, and then direct smear and gram-staining slides were prepared from fecal samples on day 21 after treatment showing that the treatment was successful in 77 percent of infected birds. However, infection was detected in 23 percent of birds, suggesting food hygiene control and using some other effective drugs such as amphotericin B.


Avian gastric yeast (Macroohabdus ornithogaster), which is more common in smaller companion birds like parrotlets, lovebirds, finches, cockatiels, and budgerigars, often colonizes the digestive tract of birds. A weakened immune system seems to be the most risk factor for the birds to be infected1. The most common sign of infection is believed to be chronic weight loss, lethargy, regurgitation with or without undigested seeds or pellets in the droppings, and diarrhea. Therefore, the droppings can return to a proper environment for both relapses and potential shedding of the infection2. The disease can be diagnosed by examining the droppings and the feces under the microscope. Both the gram-staining method and wet slides aid the diagnosis by positive identification of the organisms. As the organisms could be shed sporadically and in low numbers, repeated evaluation may be necessary1. Controlling and treatment of avian gastric yeast are always difficult for clinicians, as subclinical infections can occur in many birds. Amphotericin B is the choice medication for treatment, as many antimicrobial and antifungal medication.

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