A New Disease of Budgerigars - Osteopetrosis

Osteopetrosis is a rare disease of mammals and birds. The name means "stone bones" suggesting that the bones are even harder than normal although this is not always the case. While the disease has been diagnosed in various types of domestic poultry there appear to be no reports of it in cage birds.

The four budgerigars in which the disease was seen all belonged to the same fancier, and were from two clutches which also included some normal chicks. The condition was first noted when the birds left the nest boxes but may have been present before this.

The affected birds had difficulty in moving about but this varied in severity from bird to bird; one could only get about at all by hooking its beak into roughness on the cage floor, while another stood in a slightly crouching position, but could walk and fly, at least as far as the nearest perch. The birds had normal appetites and were in good bodily condition. Once the condition was diagnosed in the most severely affected bird the others were put down and two of the four bodies were examined post-mortem.

The post-mortem examination showed that some of the bones were thickened, especially the tibia (drumstick). Three of the bones of the wing, (humerus, radius and ulna), the ribs and the bones of the shoulders, (the wish-bone, shoulder blade and the coracoid). Not all of these bones were affected in individual birds; the one which could stand had unaffected leg bones. Diseased bones were swollen along their shafts to two or three times the normal diameter by a layer of new soft bone laid down on outside of the original shaft of the bone, which still persisted.

In addition there was new bone completely filling the marrow cavities of the affected bones. As seen in the budgerigars the affected bones were soft. In most species the new bone eventually becomes very hard and stone-like but these birds were not allowed to live long enough to see if this would happen. The bones not affected by this disease were a little soft and more easily broken than normal, possibly because of an insufficient intake of calcium for the formation of both the normal and the diseased bone. The muscles of the legs were very small although otherwise normal, and this, possibly coupled with pain, was the explanation for the birds' inability to stand properly. The small size of the muscles meant that the legs were not noticeably swollen. The wing muscles were unaffected, possibly because the underlying breast bone was normal.

In other animals there are two causes of this disease. In most mammals it is inherited; when two animals which are unaffected carriers of the disease mate, a proportion of their offspring will inherit two of the recessive genes and will go down with the disease. In domestic poultry the disease is caused by a virus which means that the conditon is infectious; however, it seems very probable that only the young chicks are susceptible to infection. When the disease in was studied many years ago, in order to get experimental cases young chicks had to be exposed to the virus at not more than a few days old but the disease did not develop for a few weeks after birds were infected.

In the cases reported here, it is not known if the disease was the inherited form or the infectious form; the parents could have been carriers of either the defective genes or the virus. However the chance of mating two sets of different males and females all of which carried the defective gene seems somewhat remote so that the infectious theory seems more probable. The fancier concerned also kept poultry and while he had not recognised the infection in them it is possible that one or more of them were carriers, and the fancier transferred the infection into the budgerigar stud; this does, however, remain unproven.

There is no treatment for this disease.

The recognition of new diseases, albeit rare ones, is one of the valuable outcomes of the veterinary service offered to members of the Budgerigar Society, as the more diseases are recognised the better will be our understanding of the causes of illness in these birds. While the poultry were not proven to be the the source of the illness this disease outbreak does suggest that totally dis-similar birds can have the same diseases - there are other diseases of poultry which can and do spread to budgerigars.

This research has been entirely funded by the Budgerigar Society.

Original text Copyright 1997, Dr John R Baker.

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