Progressive Lameness of a Greater One-Horned Rhinoceros (Rhinoceros unicornis) Associated with a Retroperitoneal Abscess and Thrombus Caused by Streptococcus dysgalactiae Subspecies equisimilis

Abstract

In rhinoceroses, lameness is an occasionally seen symptom primarily caused by lesions affecting the feet and interdigital space. A 3-year-old male Greater one-horned rhinoceros developed a progressive, severe movement disorder of the right hind limb with subsequent death. The pathological analysis diagnosed a severe, retroperitoneal abscess and chronic thrombosis of the right iliac artery. Streptococci detected in the abscess were further identified as Streptococcus dysgalactiae subspecies equisimilis by culture and molecular techniques. The identical isolate was also identified in a vaginal swab of the dam. The list of differential diagnoses for lameness in rhinoceroses must be expanded by processes affecting other than the extremities per se.

Keywords: Greater one-horned rhinoceros; Rhinoceros unicornis; Streptococcus dysgalactiae subspecies equisimilis; lameness.

Figure 1

(a) Rhinoceros in left lateral position, retroperitoneal abscess. A massive two-chambered abscess filled with over 80 L pus was located ventrally to the spine. The right iliac artery (black arrow) firmly attached to the abscess showed a precipitation thrombus. The degree of abscess formation is illustrated by yellow dotted lines. R = rectum, bar = 10 cm. (b) Thrombus of the right iliac artery, opened longitudinally. An arterial thrombus was firmly attached to the inner vessel wall over its total length, bar = 1 cm.

Figure 2

(a) Thrombotic artery. Thrombotic fibrin was firmly attached to the remnant of the vascular wall. The vascular wall did not present a regular histological architecture lacking the endothelial cells and showing only residues of smooth muscle cells (asterisk). HE 200× g magnification; bar = 50 μm. (b) Occasionally, the thrombotic fibrin was admixed with erythrocytes and neutrophils; however, no bacteria were visible. HE 400× g magnification; bar = 20 μm. (c) Surrounding tissue of thrombosed vessel showed a granulation tissue with perpendicularly aligned neovascularization admixed with chronic-active inflammatory infiltrates, predominantly characterized by neutrophilic granulocytes (arrows), HE 400× g magnification; bar = 20 μm. (d) Abscess capsule. The capsule was characterized by fibrous tissue containing fibrocytes (asterisk) admixed with a chronic immune cell infiltration including plasma cells (black arrow). Centrally, neutrophils (arrowhead) and macrophages (dotted arrow) were present. HE 400× g magnification; bar = 20 µm.

Figure 3

Detection of streptococcus in the abscess. (a) Numerous streptococci (red) were identified within cells via immunofluorescence. Nuclei of cells were detected with the DNA-binding dye DAPI (blue). 600× g magnification, bar = 20 µm. (b) Consecutive slide. Most of the cells were morphologically identified as macrophages. HE 600× g magnification; bar = 20 μm.

Figure 4

Detection of streptococci in close contact to endothelial cells of vascular structure, located in the surrounding tissue of the abscess capsule. 400× g magnification, bar = 20 µm. Nuclei of cells were detected with the DNA-binding dye DAPI (blue).