Macrorhabdus (Avian Gastric Yeast/Megabacteria)

Macrorhabdus, also known as Avian Gastric Yeast (formerly referred to as Megabacteria), is a fungal organism that colonises the lining of the proventriculus, the first section of a bird's stomach. The damage caused by this fungus can impair digestion and may lead to ulceration and haemorrhage within the gastrointestinal tract.

Clinical Signs

Birds affected by Macrorhabdus may exhibit a range of clinical signs, including:

• Weight loss

• Dirty or stained vents

• Lethargy

• Increased appetite despite weight loss

• Regurgitation or vomiting

• Sudden death

Diagnosis

Macrorhabdus can often be identified microscopically in faecal samples. However, the organism is not consistently shed in every dropping, meaning false-negative results can occur, particularly when screening apparently healthy birds. Birds showing clinical signs are generally shedding larger numbers of organisms, making detection easier.

PCR testing is also available and can be used to screen for Macrorhabdus infection.

Treatment

Treatment can be challenging, and complete eradication of the fungus is not always achievable. Unfortunately, in severe cases birds may need to be hospitalised and may still succumb to the disease within 3–5 days of commencing treatment.

In most cases, a minimum of 30 days of twice-daily oral medication is required. Some birds may require repeated or ongoing treatment to maintain control of the infection. In aviary situations where reinfection is likely, shorter treatment courses may be considered once clinical signs have resolved.

Management and Prevention

The use of probiotics in drinking water may help support healthy gut bacterial populations and improve resistance to disease. Probiotics can be administered for 2–3 consecutive days each week.

As the fungus is spread through droppings, good hygiene is essential. Daily cleaning of food and water containers, along with regular cleaning of perches, toys, and aviary surfaces, can help reduce transmission between birds.

New birds should be quarantined for 2–6 weeks before introduction to an existing flock. We also recommend having faecal samples tested within the first week of acquisition to help ensure the bird is free from infection.