Heterophilic Leukocytosis and Myeloid hyperplasia Associated with Infection in a Lesser Sulphur-crested Cockatoo (Cacatua sulphurea)

Dorothee Bienzle and Dale A. Smith

Department of Pathology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602 USA (Bienzle) and Ontario Veterinary College, University of Guelph, Guelph, Ontario ON N1G 2W1 Canada (Smith)

Abstract. A female adult Lesser Sulphur-crested Cockatoo (Cacatua sulphurea) presented with a traumatic foot lesion that was surgically debrided. The distal limb was immobilized, and the animal treated with antimicrobial drugs. Post-operatively, the bird initially appeared to recover well, however, depression and anorexia developed on day 3. A marked non-responsive anemia with a severe leukocytosis and left shift were noted on blood examination. The patient was fed through tube-administration for four days. Death on day 5 was attributed to an esophageal perforation due to trauma. Postmortem examination confirmed pulmonary collapse secondary to esophageal rupture as the immediate cause of death. Microscopic bone marrow changes consisted of myelocytic hyperplasia with erythroid hypoplasia. These changes were attributed to chronically stimulated myelopoiesis in response to a persistent infection, likely from the distal limb site. This case illustrates the ability of a psittacine bird to mount a marked heterophilic leukocytosis.

Key words: Avian, Cockatoo, Cacatua sulphurea, Leukocytosis, Heterophilia, Bone marrow

 Introduction

Psittacine birds are popular as household companion animals and in zoological collections. Many common illnesses of psittacine birds manifest with hematologic abnormalities, yet relatively little is known regarding interpretation of changes in the complete blood count (CBC). Reference ranges established for small groups of psittacine species indicated that the packed cell volumes generally exceed 45%, while leukocyte counts for clinically normal cockatoos have been reported to range from 0.6 to 10.6x10⁹/L.⁵ These leukocyte counts are lower than those reported for African Grey Parrots, ⁵ and Amazon Parrots and macaws.⁹ Heteropenias are generally thought to manifest in response to overwhelming infection, and heterophilias to result from persistent infections.³ A mild mature heterophilia has been considered characteristic of juvenile psittacine birds.⁴

The bone marrow has rarely been examined in birds with hematologic abnormalities; however, studies on the anatomy and physiology of avian bone marrow indicate that blood cell production in pigeons and chickens proceeds in a manner analogous to mammalian hematopoiesis.^8,10 The yolk sac is the site of initial hematopoiesis with progression to liver and spleen during embryogenesis, and post-hatching the marrow cavities gradually become the sole sites of blood cell synthesis. Erythropoietic activity predominates in bones of the central skeleton during the first two weeks post-hatching, with gradual transition to bones of the peripheral skeleton, in particular the femoral cavities, during maturation.⁸ The skull, the majority of the vertebral column, the ribs, the coracoid, and the humeri are pneumatized in the adult, and do not contribute to hematopoiesis. Transformation of active marrow into fatty tissue started after the age of 4 weeks in pigeons.⁸ Thus, sampling bone marrow from a leg bone in a bird should yield diagnostically useful information in cases with hematologic abnormalities.

In this report severe leukocytosis with a marked anemia in a mature cockatoo is described. The bird had evidence of a bacterial infection involving the distal leg, and responded with a marked heterophilia. Bone marrow examination at necropsy confirmed profound myeloid hyperplasia and erythroid hypoplasia.

Case Report

A mature female Lesser Sulphur-crested Cockatoo (Cacatua sulphurea) was presented with a history of having caught a wing in the cage, and subsequent self-mutilation of the right foot distal to the hock. The animal was in fair to good condition with reduced muscle mass and fat stores. The tendons at the distal limb site were exposed, and there was extensive swelling and an exposed joint space. The bird was anesthetized, and the wound surgically debrided. Post-operatively systemic and local antimicrobial therapy was administered. The wound appeared to heal during the subsequent days; however, the bird became anorexic on day 4. Tube feeding and iron supplementation were initiated. The patient died imminently following tube administration of feed on day 6. Hematologic evaluation had indicated that the bird was anemic at presentation, and that the anemia did not improve during the course of hospitalization (Table 1). A severe leukocytosis consisting of a heterophilia with a left shift was noted on day 3. Biochemical abnormalities included moderate elevations in serum creatine kinase and aspartate aminotransferase (AST), and hypoproteinemia (Table 2).

Necropsy examination identified a perforation of the esophagus proximal to the thoracic inlet. Feed material was noted in the thoracic cavity. Microscopically, focal areas of congestion were noted in the liver and interstitial congestion in the kidneys. Basophilic deposits consistent in appearance with urates were identified on the epicardial surface. The perforation in the esophagus was associated with a moderate number of bacterial and fungal organisms; however, inflammatory infiltrates and fibrosis were absent. Femoral bone marrow was solidly cellular (Fig. 1), and consisted of approximately 70% granulocytic precursor cells. The majority of myelocytic cells had prominent cytoplasmic granules that ranged from small, brightly orange-staining to larger, round granules with a more basophilic appearance (Fig.2).

Fig. 1. Cockatoo, femur, H&E stain. Bone marrow hyperplasia is present.	Fig. 2. Cockatoo, bone marrow, H&E stain. Myeloid hyperplasia is evident.

Erythroid precursor cells were present in sinusoids scattered throughout the marrow, and at increased frequencies immediately paratrabecular. Maturation of the erythroid cells appeared incomplete as few fully hemoglobinized rubricytes with oval nuclei were apparent (Fig. 3). The majority of rubricytes had round nuclei and an open chromatin pattern. Iron stores were not identified.

Fig. 3. Cockatoo, bone marrow, H&E stain. Developing rubricytes in a sinusoid are surrounded by developing heterophils in the extrasinusoidal parenchyma.

Death in this bird was attributed to acute pulmonary collapse secondary to esophageal rupture.

Discussion

This bird presented with a foot lesion presumed to be less than 48 hours in duration. Surgical debridement of the lesion and subsequent response to antimicrobial therapy suggested that bacterial infection contributed to the inflammation at the site. Post-operatively, the lesion appeared to heal appropriately, however, anorexia developed two days later indicating incomplete control of the initial lesion, or development of a secondary problem. The animal was tube-fed resulting in perforation of the esophagus on the sixth day. On microscopic examination no signs of chronicity at the margins of the esophageal rupture were identified, thus, the esophageal lesion was not considered the cause of anorexia. No other inflammatory foci were recognized at necropsy, therefore the foot lesion and possible subclinical bacteremia were likely the inciting causes for the marked heterophilia. The presence of a left shift indicated that the marrow was not able to maintain production of mature heterophils in response to peripheral demand. Though the rapidity and magnitude of granulocyte responses in psittacine birds are largely unknown, birds of prey have been described to sustain leukocyte counts exceeding 100x10⁹/L with chronic infections.² Similarly, chemically-induced inflammation in chickens resulted in leukocyte counts surpassing 50x10⁹/L within 3 days in the absence of an infectious stimulus.⁶ Hence, it appears possible that psittacine birds such as the case described will mount a leukocytosis of this magnitude in response to an infection, and possibly within less than 5 days.

The anemia noted in this cockatoo was marked, and microcytic as well as hypochromic (Table 1). Polychromatic cells were rare. Though mild anemia may accompany chronic illness in psittacine birds,⁷ the degree of this anemia was suggestive of a primary bone marrow production problem. Hypochromasia and microcytosis are suggestive of iron deficiency in mammalian species, which may have contributed to the anemia in this case. Specific evaluation of iron status in avian species is not available, and neither bone marrow nor organs of the reticulo-endothelial system were noted to store intravenously administered radioactive iron in pigeons.⁸ Considering the severity of the anemia, and the disproportionately mild decrease in total protein concentration, it appeared likely that the anemia preceded the traumatic event, and that blood loss associated with the wound and surgery exacerbated the decrease in packed cell volume. Whether chronic iron deficiency associated with malnutrition pre-existed in this case was unknown, albeit, the bird’s fat stores were judged to be reduced.

The high cellularity of the bone marrow in this bird is different than what has been observed in the ulnae of mature, clinically normal chickens.¹⁰ Studies in pigeons indicated that mature erythropoietic bone marrow is gradually replaced by fatty infiltrates and assumes a progressively smaller percentage of the total body weight with increasing age.⁸ Albeit, the femora represented more than one third of the total erythropoietic activity observed, thus the ulnae of chickens may normally consist of less active marrow. It appears unlikely that the femoral marrow in the case reported here converted to such high cellularity within a 6 day period, thus either the site sampled represents the most active blood cell synthetic focus in the body with normally high cellularity, or the bird had a more chronic leukocytic stimulus than evident from the history provided.

The increased enzyme activities in this case were attributed to leakage from myocytes associated with the initial wing trauma, and the subsequent foot lesion. Though AST activity has been noted in many different avian tissues, and increases have been clinically associated with liver disease and septicemia in psittacine birds,¹ the concurrence with elevated CK activity in this case was most consistent with muscle origin. Hypoproteinemia may have resulted from chronic malnutrition, impaired hepatic synthesis, or from blood loss. Absence of biochemical or microscopic evidence of liver disease suggests that a combination of the former factors contributed to the decreased protein concentration observed.

This case illustrates the ability of a psittacine bird to mount a marked heterophilia in response to an inflammatory and/or infectious stimulus. The bone marrow findings were consistent with increased granulopoiesis and reduced erythropoiesis. The demise of the patient appeared unrelated to an appropriate hematologic response to an inflammatory lesion.

References

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2. Bienzle D, Pare JA Smith DA: Leukocyte changes in diseased non-domestic birds. Vet Clin Pathol 26:76-84, 1997.

3. Campbell TW: Avian Hematology and Cytology. Iowa State University Press, Ames, 1988, p. 17.

4. Clubb SL, Schubot RM, Joyner K, et al. : Hematologic and serum biochemical reference intervals in juvenile cockatoos. J Assoc Av Vet 5:16-26, 1991.

5. Hawkey CM, Samour HJ: The value of clinical hematology in exotic birds. In: Jacobson ER, Kollias GV (eds): Contemporary Issues in Small Animal Practice, Exotic Animals. Churchill Livingstone, New York, 1988, pp. 109-141.

6. Latimer KS, Tang KN, Goodwin MA, et al. : Leukocyte changes associated with acute inflammation in chickens. Avian Dis 32:760-772, 1988.

7. Oglesbee BL: Hypothyroidism in a scarlet macaw. J Am Vet Med Assoc 201:159-1601, 1992.

8. Schepelmann K: Erythropoietic bone marrow in the pigeon: development of its distribution and volume during growth and pneumatization of bones. J Morphol 203:21-34, 1990.

9. Tangredi BP: Heterophilia and left shift associated with fatal disease in four psittacine birds: yellow-collared macaw (Ara auricollis), yellow-naped Amazon (Amazona ochrocephala), yellow-crowned Amazon (Amazona ochrocephala ochrocephala), blue and gold macaw (Ara ararauna). J Zoo Anim Med 12:13-21, 1981.

10. Valverde A, Bienzle D, Smith DA, et al. : Intraosseous cannulation and drug administration for induction of anesthesia in chickens. Vet Surg 22:240-244, 1993.

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