Pathologic and immunohistochemical findings in an outbreak of systemic toxoplasmosis in a mob of red kangaroos

Abstract

Toxoplasma gondii is a zoonotic protozoan pathogen that infects many endothermic vertebrates, including humans; the domestic cat and other felids serve as the definitive host. Macropodids are considered highly susceptible to toxoplasmosis. Here, we describe the clinical, pathologic, and immunohistochemical findings of an outbreak of systemic toxoplasmosis in a mob of 11 red kangaroos (Macropus rufus), with high morbidity (73%) and mortality (100%) rates. Affected animals had either severe and rapidly deteriorating clinical conditions or sudden death, which was correlated with widespread necrotizing lesions in multiple organs and intralesional T. gondii organisms identified via MIC3-specific immunohistochemistry and confirmed by REP529-specific rtPCR. Quantification of parasites demonstrated the highest parasite density in pulmonary parenchyma compared with other tissues. Our study highlights the continued importance of this severe condition in Australian marsupials.

Keywords: Apicomplexa; Toxoplasma gondii; histopathology; immunohistochemistry; red kangaroos; toxoplasmosis.

Figure 1.

Acute toxoplasmosis in red kangaroos. A. Macroscopic view of the lower respiratory tract and B. cut surface of the pulmonary parenchyma. The pulmonary parenchyma was mottled to diffusely purple or dark-red, firm, and failed to collapse.

Figure 2.

Histologic and IHC findings in tissues with the highest Toxoplasma gondii burden. A. Pulmonary vessels are congested and delimited by lymphocytic, plasmacytic, and histiocytic perivascular cuffs. Alveoli are diffusely filled with alveolar macrophages and fibrin. Inset: occasional parasitophorous vacuoles containing zoites are identified presumably within the cytoplasm of histiocytes or other interstitial cells. B. High numbers of tachyzoites (arrowheads) and occasional parasitophorous vacuoles with zoites (arrow) are readily identified via IHC in the pulmonary parenchyma. C, D. The myocardium is multifocally disrupted by necrosis, inflammation, and early fibroblastic proliferation. Occasional intralesional parasitophorous vacuoles containing zoites are identified with hematoxylin and eosin stain (inset) and (D) by IHC. E, F. Hepatic portal areas are infiltrated by mixed inflammatory cells that transmigrate and disrupt the biliary duct epithelium. Intrahepatocellular zoites within parasitophorous vacuoles are rare (inset) and (F) more easily detected via IHC.

Figure 3.

Histologic and IHC findings in other tissues. A. The zona fasciculata of the adrenal gland is disrupted by necrosis and hemorrhage with intralesional parasitophorous vacuoles containing zoites (inset). B. Intralesional parasitophorous vacuoles (arrow) and tachyzoites (arrowheads) are readily detected in the adrenal gland via IHC. C, D. Similar areas of necrosis and reactive glial cell proliferation are evident in nervous tissues including (C) the brainstem and (D) cerebellum with rare intralesional parasitophorous vacuoles or tachyzoites identified via IHC (C, inset). E. Ocular lesions were characterized by inflammatory cells (lymphocytes, plasma cells, and histiocytes) multifocally dissecting the choroid layer (arrows). F. The optic nerve was infiltrated by numerous reactive glial cells and lymphocytes. Inset: rare parasitophorous vacuoles containing zoites were identified. H&E.

Figure 4.

Histologic and IHC findings in other tissues (continued). A. The tunica muscularis of the stomach and small intestine are multifocally disrupted, with infiltrating lymphocytes, plasma cells, and histiocytes. Inset: rare parasitophorous vacuoles containing zoites were recognized via IHC. B. The corpus luteum contained small amounts of karyorrhectic debris and a few infiltrating lymphocytes and neutrophils. Inset: rare luteal cells contained intracytoplasmic parasitophorous vacuoles with zoites.

Figure 5.

Specificity of 2 anti–Toxoplasma gondii antibodies (anti-MIC3 T4 2F3 monoclonal antibody [A, C, E] and anti–T. gondii RH strain [whole parasite] polyclonal antibody [B, D, F]) as determined by immunohistochemistry in bovine turbinate cells infected with T. gondii RH strain (A, B), Neospora caninum Liverpool strain (C, D), or Sarcocystis neurona SN3 strain (E, F). Anti-MIC3 T4 2F3 is specific for T. gondii (A). The polyclonal antibody to T. gondii shows cross-reactivity with N. caninum (D) but not with S. neurona (F).