Avian gastric yeast (aka megabacteria): should you be worried
Avian Gastric Yeast (aka Megabacteria): Should You Be Worried?
by David N. Phalen, DVM, PhD, Dipl. ABVP (Avian)
Schubot Exotic Bird Health Centre and The Department of Large Animal Medicine and Surgery
Texas A&M University College Station, TX 77843 This article first appeared in the Newsletter of the Midwestern Avian Research Expo, 2001.
Veterinary students, aviculturalists, and pet bird owners all have one thing in common, they
always have to be worried about something. The question that I want to address here is whether
bird owners should be worried about megabacteria? The comments that I am about to make are
based on my experience and knowledge of the literature. Many things have been said about this
organism and diseases associated with it, but as of yet, there is little good experimental data to
support many of those claims.
The first question that we need to answer is what is this organism anyway? Work in my
laboratory by Dr Elizabeth Tomaszewski has shown that it is a type of fungus, a yeast. This is in
agreement with work that has also been done in Germany. Therefore, I will refer to this
organism as the avian gastric yeast (AGY)
for the rest of this article. Our work contrasts with
previous work that suggested that this organism was a bacteria. It is my opinion that scientists
that have reported that they have grown this organism using traditional bacterial isolation
methods have grown bacteria that live in the ventriculus, but have not grown the AGY itself.
Because AGY is a fungus, it will only be expected to respond to specific drugs that are effective
The AGY has been identified in many species of birds, but it is particularly common in
budgerigars, some species of finches, and it is the general impression that it commonly infects
parrotlets. From our research and based on conversations with aviculturalists and veterinarians,
there is a suggestion that this organism may commonly infect the green-naped parrotlet and may
be more likely to cause disease in parrotlets that have been bred for colour mutations. Rumours
abound and one rumour is that there is more than one AGY and that some are more likely to
cause disease than others. This point is totally speculative and our data at this time, do not
support this hypothesis.
Does AGY cause disease? Does it cause disease in all birds that it infects or just some?
Although, I personally have rarely seen birds that I thought had disease caused by the AGY,
work in Australia, Europe and reports from veterinarians here in the United States' suggest that it
does cause disease in some infected birds. In the budgerigar, the disease most commonly
associated with AGY is termed “going light.” These are typically older birds and they typically
have a long course of disease characterised by weight loss and regurgitation. Birds with this
disease will have large numbers of the AGY in their droppings and when treated with an
appropriate drug will become clinically better and the AGY will no longer be found in the
droppings. It is important to note that other diseases, including trichomoniasis, can also cause
these same signs in budgerigars. In other species of birds, AGY has been associated with a
chronic wasting disease, but regurgitation has not been reported to me, at least, as a common
sign. These birds also shed large numbers of organisms and signs resolve with treatment.
The AGY, however, does not cause disease in all infected birds. Currently I have a research
flock of budgerigars. At one time or another, most of these birds have shed AGY. Yet, none of
these birds show any signs of disease that could be related to this organism. I have made similar
observations in other budgerigar collections. So I am going to go out on a limb and tell you that
I think that most budgerigars infected with AGY are just fine and healthy and that only a small
percentage of infected birds actually develop AGY-associated disease.
Diagnosis of AGY infection is not always easy. AGY does not stain well with the Gram stain or
quick stains. It is readily observed in a slurry made of a dropping and saline, but not all infected
birds shed the organism in sufficient concentrations so that it can be detected with one or more
samples and other organisms in the faeces may be mistaken for AGY.
The final questions about AGY revolve around treatment. Can we treat this organism in the sick
bird and expect improvement? What about flock treatment? Does it make sense to be treating
entire collections of birds? The best information on this topic is from Dr Lucio Filippich at the
University of Queensland, Australia. Dr Filippich has shown that AGY can be treated with
amphotericin B and that sick birds get better with treatment. However, at least in budgerigar
collections, treatment is not 100 per cent affective and some birds remain infected and
presumably will re-infect the others after treatment has ended. Our work has also supported this.
We have used two different preparations of amphotericin and found that in two weeks, many
birds will become negative, but low levels of infection will persist in other birds. Four weeks of
treatment, however, showed a complete cure in one of our studies. Another drug that we have
studied, fluconazole, was effective against the organism in most birds, but did not eliminate it
from all birds treated.
At this point in time, my conclusions about the avian gastric yeast are the following. Infection
with AGY is very common in some species of birds, but disease is rare. No treatment trials,
except 30 day treatment with amphotericin, have resulted in the elimination of AGY from a
flock of birds. Individual birds showing signs of illness may respond to treatment. In my opinion
treating sick birds makes sense. However, treating entire flocks of birds that do not show signs
of disease does not make sense because I do not think it can be eliminated from an entire flock
and we may cause the organism to become resistant to the drug we are using. Should a bird be
eliminated because it is found to have this organism in its droppings? I would say no. If you are
sure that none of your other birds have this infection. then don’t bring it into your collection. But
if you have a nice healthy fat and cheery parrotlet or budgerigar with small numbers of
organisms in the droppings, I do not consider this to be a problem. I am sure that other
veterinarians may disagree with me and I may change my opinion as we learn more about this
organism, but for now, this is what I think. Acknowledgement
This article by David N. Phalen is supplied by the World Budgerigar Organisation
, as part of their encouraged exchange of research information, and
supplied to the WBO with kind permission by the Budgerigar Association of America
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