Megabacteria in Diseased and Healthy Budgerigars

Megabacteria are associated with disease and death in Budgerigars and a range of other birds. They inhabit the proventriculus or true stomach where they cause changes in the structure and function of the organ. The proventriculus becomes dilated and the wall thickened; the production of digestive juices is impaired; excess mucus is produced and there may be ulceration at each junction of the proventriculus and gizzard. The disease is extremely common in exhibition Budgerigars in the UK and is the major cause of illness and death in these birds.

Megabacteria Carriers

It was believed that apparently healthy birds could carry this infection and live in balance with it, and that these birds were responsible for spreading the infection from stud to stud as birds were bought, sold and exhibited. Some vets, and others, believe that megabacteria are normal inhabitants of the bird's stomach, and that some other disease is responsible for the changes in the proventriculus which allows the number of megabacteria to increase. No proof of this has ever been produced so work was carried out to establish whether carriers existed or not. Was megabacteria after all, simply a normal inhabitant of the proventriculus? It was also hoped that it would be possible to demonstrate the role of megabacteria in causing proventricular disease.

Diagnostic Focus on Megabacteria

As part of the Budgerigar Society diagnostic service, dead Budgerigars are examined post-mortem. In 160 birds received over the last few months, particular attention has been paid to the proventriculus, and this organ has been examined for megabacteria regardless of the cause of death. The results were as in the table below.

Results of Diagnostic Focus

	With Megabacteria	Number of birds	% of birds in the group
Birds with normal proventriculi	Yes	28	33
	No	57	67
Birds with abnormal proventriculi	Yes	69	92
	No	6	8

High Numbers of Carriers

As only one-third of the birds with normal proventriculi have megabacteria in the organ, the bacteria cannot be considered to be a normal inhabitant of this part of the Budgerigar. However, in most other diseases where clinically normal carriers are present, they form a lower percentage of the population than this. A possible reason for the high prevalence of clinically normal carriers, is the very high prevalence of the clinical disease which results in large numbers of healthy birds being exposed to the infection and becoming unwell or carriers of the infection.

Other Causes of Abnormal Proventriculi

The birds with megabacteria infection of an abnormal proventriculus showed changes, such as an excess of mucus in the organ or a minor degree of dilation, thickening of the wall, and ulceration at the junction of the gizzard and proventriculus. Many of these birds had been clinically ill but, in some of the cases of birds with minor lesions, the birds had died of other causes. While nearly all cases of abnormal proventriculi were due to megabacteria infection, a few were not. In this survey six birds had abnormal proventriculi due to:

• In two cases, E. coli infection.
• In two cases, ulcers.
• In one case, a cyst.
• In one case, of excess mucus production of an unknown cause.

Conclusions

For a small survey it can be seen that:

1. Proventricular disease is almost always due to megabacteria infection.
2. That there are many clinically normal carriers in the Budgerigar population which can go either up or down with the infection when subjected to stress, or remain as carriers posing a risk to un-infected birds they come into contact with.
3. Megabacteria do not appear to be normal inhabitants of the proventriculus of Budgerigars.

Original text Copyright 1997, Dr John R Baker.

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