"Searching for the Mysterious Killer of the Great - Billed Parrots" --by David N. Phalen, DVM, PhD, Dipl. ABVP (Avian)
© October, 2002
everal years ago, I was asked to investigate an apparently high incidence of disease and death in great-billed parrots (Tanygnathus megalorynchus ). To this end, a two pronged investigation was initiated. The first phase of the investigation was to document the high death-rate that was thought to be happening and to see if there were any husbandry or geographic related factors that might be predisposing to this apparently high death rate. The second phase of the investigation was to collect as many pathologists' reports as possible from birds that had previously died and to have any birds that subsequently died submitted to me so that a complete and consistent necropsy could be done.
The results of the survey were unexpected and of great concern. It was found that of all great-bills in the United States belonging to the respondents, approximately 35% had died in the period of 1995-2000 and in the Southern United States, nearly 50% of all great-billed parrots had died during this period. Clues to the cause of death in these birds were not obvious. Most of the birds that died were housed out-of-doors in wire cages, but this is the standard means of caging in the South so it was not clear if the deaths might be associated with the type of caging, being housed outdoors, or being housed outdoors in the South.
The pathologists' reports were somewhat helpful, but did not create a clear picture as to what problems we were facing. Some birds died from known diseases such as aspergillosis and zinc poisoning. Other reports did not give a confirmed cause of death. A cluster of cases came from Florida. These birds died in the late summer or fall. Specific signs of disease in these birds were fairly consistent and there was evidence that many of these birds had some form of gastrointestinal disease. Unfortunately, neither the survey of great-billed owners nor the pathologists' reports gave us a definitive explanation for the great-bills' deaths.
It has only been in the past two year that I have actually had great-bills that had died submitted to me for examination. Several were submitted from a Florida outbreak that occurred in the Fall of 2001. Key findings in these birds included degeneration of heart and skeletal muscle and a suggestion of degeneration of portions of the brain. These findings closely resembled vitamin E or selenium deficiency as seen in poultry. This prompted me to advise great-billed owners to make sure that their birds diets that contained a significant proportion of foods rich in vitamin E, e. g., seeds and nuts.
It was only this fall that I had the chance to experience this disease first hand and with the data that was collected from these outbreaks my perspective on this disease changed. First, it is clear that other birds in addition to great-bill parrots are susceptible to this disease. In the outbreak with which I was the primary clinician, Mealy Amazon parrots and a lory also died. Clinical signs of this disease were dramatic. The motility of the digestive tract shuts down. Birds may have diarrhea or no droppings at all. Even liquid diets do not pass through the digestive tract. These birds become rapidly dehydrated and most die within 1 to 3 days. Death occurrs despite aggressive therapy. Blood counts and clinical chemistries show a moderate drop in the total white blood cell count, concentration of the blood from dehydration, an imbalance of electrolytes, elevation in muscle enzymes, and an elevation in uric acid, indicating severe dehydration or primary kidney disease or a combination of both.
Post mortem findings were consistent with previous outbreaks. Degeneration of heart and skeletal muscle was a common finding. Subtle changes in the brain, suggesting degeneration of specific areas of the brain, were also seen. New lesions, not previously recognized were also found, including a moderate to severe lesion of the blood filtering portion of the kidney (the glomerulus) and a subtle change in the nerves of the digestive tract. Re-examination of the tissues from birds from previous outbreaks also demonstrated some of these changes. The kidney lesion is one that is often associated with the deposition of antibody and antigen, the type of reaction that we expect to see with chronic infections. The nerve lesions are very unusual and their potential cause is not known. Two birds also had unusual forms of pneumonia and air sacculitis. Attempts to find an infectious agent that might cause all these lesions were unsuccessful. Discussions with other pathologists suggest that this disease was seen by them, but was not recognized as a specific entity.
The work done to date shows that there is in fact a disease that is targeting great-billed parrots. Significantly, however, it is not limited to great-billed parrots and it may be a more common disease than previously thought. It is clear that this disease occurs predominately in the late summer and early fall and birds in the Southeastern and Southcentral states are at greatest risk. The patterns of disease seen in the outbreaks that were studied suggest that this is an infectious disease. An insect borne disease is possible, although it is also possible that some of the infected birds may have become infected by movement of the infectious agent on caretakers. A toxin cannot be completely ruled out as the cause of this problem, but the circumstantial evidence collected to date is not consistent with a toxin as the cause.
Efforts to determine the cause of this disease continue. A collaboration with investigators at the CDC was established to look for insect borne viruses. Also, tissues from the birds that died were saved for additional testing. A publication on these findings is being written, so that others can recognize the disease and additional information can be gathered. Ultimately, the success of our work will depend on funding. Dr. Tizard, Director of the Schubot Exotic Bird Health Center has been very generous in supporting this research. Money raised by the Midwestern Avian Research Expo and private individuals has also helped. Ideally, however, a specific investigator or graduate student would take on this project on a full time basis. This would require an investment of many thousands of dollars each year for several years. This type of funding, however, is very rare in the field of exotic bird medicine. Therefore, we will continue to work with the funds that we get and with the time that we have. With luck we will be successful and the cause of this disease and a means of prevention will be found.
Update - June, 2003
--© David N. Phalen, DVM, PhD, Dipl. ABVP (Avian) 2000
Associate Professor, Zoological Medicine Section
Assistant Director, Schubot Exotic Bird Health Center
Texas A&M University
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