An Outbreak of Fatal Disease in Peach-faced Lovebirds (Agapornis roseicollis) Attributed to an Unidentified Protozoan Parasite
Michele V. Hawk, L. L. Munger, and H. John Barnes
Department of Food Animal and Equine Medicine, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough Street, Raleigh, North Carolina 27606 (Hawk, Barnes) and Rollins Animal Disease Diagnostic Laboratory, PO Box 12223, Raleigh, North Carolina 27605 (Munger)
Abstract. In September of 1997 three Peach-faced Lovebirds (Agapornis roseicollis) were presented for necropsy at a diagnostic laboratory in North Carolina. Large protozoan cysts were found in the lung and liver of the one bird from which tissues were collected. The protozoan cysts had a thin eosinophilic wall and contained basophilic granular material. Based on size and morphology, the protozoan cysts resembled megaloschizonts of Leucocytozoon sp. or Haemoproteus sp. However, because gametocytes were not found in the blood cells, the etiologic agent could not be definitely identified and is possibly not a blood parasite. Until more information is obtained, we determined that the organisms were most appropriately identified as haemosporozoa of undetermined taxonomic status, a designation that is used by Gardiner et al. 2
Key Words: Haemosporozoa, Leucocytozoon, Haemoproteus, Protozoa, Lovebird, Parasite, Agapornis roseicollis
Introduction
Several protozoan parasites form cyst-like structures in the tissues of avian hosts including microsporidia, Eimeria sp. , Isospora sp. , Caryospora sp. , Sarcocystis sp. , a Besnoitia-like organism, Toxoplasma gondii, Hepatozoon sp. , Plasmodium sp. , Haemoproteus sp. , Leucocytozoon sp. , and Arthrocystis sp. 2,3 Large unidentified protozoan cysts have also been found in a variety of bird species and tissue sites, which have been referred to as "haemosporozoa of undetermined taxonomic status. " 2
The purpose of this report is to alert veterinarians to a fatal disease associated with protozoan tissue cysts that were found in exotic birds in North Carolina. Because these parasites are difficult to identify in tissue sections, clinicians are encouraged to examine blood smears when such a disease is suspected.
Case Report
Case history: Two male and one female adult Peach-faced Lovebirds (Agapornis roseicollis) were submitted for necropsy to the Rollins Animal Disease Diagnostic Laboratory in Raleigh, North Carolina. The birds were owned by an individual who lived near Raleigh. They were housed in an outdoor aviary with rabbits cohabiting the floor. The birds belonged to a group of 15 that had been purchased approximately three weeks earlier from another aviary in North Carolina. Six of the 15 birds had died since the time of purchase.
Gross pathology: The two males were in moderately good nutritional status, but their tissues were severely autolyzed, precluding detailed examination. Lesions were not noted in these birds. The female was in good body condition and not decomposed. The liver of this bird was friable with some free blood around it. There also was a large area of hemorrhage on the heart, and the intestines were distended with dark, bloody contents.
Histopathology: Only tissues from the female lovebird were examined. Numerous cyst-like structures, resembling megaloschizonts, were present within the liver and the blood vessels of the lungs. In the lung, granulocytes often surrounded cysts and there was a lack of erythrocytes in pulmonary capillaries. Infrequently, blood was pooled around cysts in the liver. Cysts ranged up to approximately 200 micrometers in size. Most cysts in the liver were single and round or oval (Fig 1). In the lung the structures were more irregular in shape, often conforming to the structure of the blood vessels (Fig 2).
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| Fig. 1. Peach-faced Lovebird, liver, H&E stain. Large parasitic cysts are randomly scattered throughout the liver. |
Fig. 2. Peach-faced Lovebird, lung, H&E stain. Large parasitic cysts occlude the lumina of some pulmonary blood vessels. |
Occasionally multiple cysts were aligned adjacent to each other within pulmonary vessels, giving the appearance of elongate, septate structures (Fig 3). Cyst walls were thin and not easily visualized. In cases where the wall could be delineated, it was eosinophilic when stained with hematoxylin and eosin. Many cysts were completely filled with a dense, granular, basophilic material composed of coccoid structures surrounded by a pale halo suggestive of merozoites. Other cysts contained globular, ovoid forms approximately 5 to 30 micrometers in diameter (Fig. 4).
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| Fig. 3. Peach-faced Lovebird, lung, H&E stain. Multiple, adjacent, parasitic cysts are present within a large pulmonary blood vessel. |
Fig. 4. Peach-faced Lovebird, liver, H&E stain. Parasitic cysts are filled with dense, granular, basophilic material. |
The wall and contents of the protozoan cysts stained gram-negative and were not specifically stained with Ziehl-Neelson acid-fast stain, Gomori’s methenamine silver (GMS) stain, or periodic acid-Schiff (PAS) reagent. Cysts were best visualized with Giemsa stain.
Heart, spleen, kidney, proventriculus, intestine, pancreas, and female reproductive tract were examined but did not contain cysts. Extensive myocardial hemorrhage dissected between myocardial fibers to the external surface of the right ventricle. Sections of intestine were distended with intraluminal blood from an undetermined source. No parasitic forms were noted in blood cells within the histologic sections.
Discussion
The cause of death in the lovebird was likely due to acute hypoxia from occlusion of blood vessels in the lungs by parasites and thrombi. Alternatively, the bird may have died from internal hemorrhage as evidenced by large amounts of blood in the intestinal lumen and surrounding the liver.
Hemorrhage is many times associated with protozoan cysts in tissues of birds. Panigrahy described free blood in the thoracoabdominal cavity of 11 canaries with protozoan cysts in the liver. 4 Fowler and Forbes described cases of birds with cysts of aberrant Leucocytozoon sp. 1 Typical findings included gelatino-sanguineous exudate in the pericardial sac with myocardial and epicardial hemorrhages. Free blood was sometimes seen in the thoracoabdominal cavity.
Identification of the parasite by examination of histological sections may be impossible. Based on size and morphology, the cystic structures in the lovebird of this report closely resemble megaloschizonts of Haemoproteus sp. or Leucocytozoon sp. However, without the diagnostic presence of gametocytes within blood cells, the organism cannot be positively identified as belonging to either of these two genera, nor can it be shown even to be a blood parasite. Nonetheless, the tissue stages of this organism appear to be most compatible with protozoa designated by Gardiner et al. as haemosporozoa of undetermined taxonomic status. 2 Until more definitive information can be obtained, we believe that the organisms in this Peach-faced Lovebird also should be classified similarly (haemospora of undetermined taxonomic status).
Efforts to elucidate the identity of these protozoan cysts are on-going. The results of these investigations will be submitted for future publication elsewhere.
Acknowledgments
We would like to thank the following individuals for their help in our attempts to identify the protozoan organisms in this Peach-faced Lovebird: Dr. James S. Guy at North Carolina State University; Dr. J. P. Dubey with the U.S. Department of Agriculture in Beltsville, MD; and Dr. Greg Hall at the University of Georgia.
References
1. Fowler NG, Forbes GB: Aberrant Leucocytozoon infection in parakeets. Vet Rec 91:345-347, 1972.
2. Gardiner CH, Fayer R, Dubey JP: An Atlas of Protozoan Parasites in Animal Tissues. U.S. Department of Agriculture, Agriculture Handbook No. 651, 1988.
3. Opitz HM, Jakob HJ, Wiensenhuetter E, Devi VV: A myopathy associated with protozoan schizonts in chickens in commercial farms in peninsular Malaysia. Avian Pathol 11:527-534, 1982.
4. Panigrahy B, Harmon BG, Grumbles LC: Hemorrhagic disease in canaries (Serinus canarius). Avian Dis 28:536-541, 1984.
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