Disseminated Histoplasma capsulatum var capsulatum infection in a captive mara (Dolichotis patagonum)

HISTOPLASMOSIS, caused by Histoplasma capsulatum var capsulatum, is a widely distributed fungal disease of human beings and other mammals that occurs more commonly in certain geographical areas, such as those with humid temperate climates. H capsulatum is a dimorphic facultative intracellular parasite, which develops a virulent yeast phase with oval cells 1·5 to 3 x 3 to 4 μm in size, which are found especially in the tissues of infected animals. Infection is acquired from the environment, usually by inhalation of infective mycelial phase propagules, which consist of oval microconidia, 2 x 4 μm in diameter, thin 1·2 to 1·5 μm hyphal fragments and spherical macroconidia 8 to 15 μm in diameter (Tewary and others 1998). Histoplasma species are parasites of the mononuclear-phagocytic system, and this facilitates the pathogens’ dissemination throughout the body of susceptible hosts (Tewary and others 1998). Histoplasmosis can have a protracted course, with disease being inapparent for months or even years; pulmonary, intestinal, lymphoid, hepatic and adrenal involvement are most frequent. There is a wide range of clinical signs, including depression, weight loss, fever, anorexia, lymphadenomegaly, diarrhoea, respiratory signs (dyspnoea, coughing and abnormal lung sounds) and abortion (Wolf 1990, Jubb and others 1993). This short communication describes a case of histoplasmosis in a captive mara (Dolichotis patagonum). A two-year-old captive-born male mara weighing 4·5 kg died shortly after presenting with weakness and anorexia at Africam Safari, a wildlife park in Puebla, Mexico (2120 m above sea level). The mara colony at the park is provided daily with water ad libitum and a diet composed of oranges, carrots, chopped alfalfa and rabbit pellets; the enclosure is 120 m2, fenced with wire mesh and bamboo to a height of 1·20 m on one side, and provided with a 15 m2 shelter; the substrate is sand, and there are no sanitary footbaths at the entrance to the enclosure. At postmortem examination, the mara had a poor body condition, with depleted fat stores and moderate to severe generalised muscular atrophy. The haircoat was dry, dull and fragile. Acute, bilateral, asymmetrical, well delineated cutaneous lacerations, attributed to cagemate aggression, were found on the dorsum and less prominently on the limbs; concurrent with these lesions there were foci of epidermal crusts associated with locally extensive dermal and subcutaneous haemorrhage. There was mild to moderate ascites. The sternal and gastrohepatic lymph nodes were markedly enlarged, and greyish-brown on the cut surface, with no visible separation between the cortex and medulla. There was moderate splenomegaly and hepatomegaly; the liver had an irregular surface, with multiple to coalescing foci of whitish discoloration throughout its parenchyma (Fig 1) and a firm consistency on the cut surface. The small intestinal contents and mucosa, especially in the ileum, were red. The caudal oesophagus had multiple, coalescing, raised yellow or red lesions. The normal corticomedullary architecture of both adrenal glands was inapparent, and they had white streaks and a firm consistency on the cut surface. Touch imprints from the lymph nodes revealed large numbers of macrophages, lymphocytes and plasma cells, and fewer multinucleate cells. Most of the phagocytic cells had numerous cytoplasmic yeast-like organisms, 2 to 4 μm in diameter, with a clear halo surrounding them. Liver and adrenal touch imprints revealed abundant epithelial cells (hepatocytes and finely vacuolated adrenocortical cells, respectively) and macrophages, both with numerous similar cytoplasmic yeast-like organisms, and erythrocytes and neutrophils. Smears of the abdominal fluid revealed mixed inflammatory cells, mostly macrophages, occasionally with cytoplasmic yeast-like organisms, and fewer neutrophils. Tissues collected at postmortem examination were fixed in 10 per cent buffered formalin, embedded in paraffin, sectioned at 5 μm and routinely stained with haematoxylin and eosin; sections of the liver and lymph nodes were also stained with Gomori’s methenamine silver. Microscopically, the liver was diffusely infiltrated by numerous macrophages and plasma cells, and fewer neutrophils and lymphocytes, and had abundant fibrous tissue. There were small foci of coagulative and lytic hepatocellular necrosis infiltrated with neutrophils, moderate to severe hyperplasia and mucous metaplasia of the bile ducts, and atrophy of the few remaining hepatic cords, with sinusoidal dilation. The macrophages and, to a lesser extent, hepatocytes were laden with numerous oval organisms, 2 to 4 μm in diameter, with a central or eccentric, basophilic, round centre surrounded by a clear halo. The lymph nodes were diffusely infiltrated with numerous macrophages and fewer multinucleate giant cells with similar cytoplasmic organisms; plasma cell infiltrates were also prominent and there was marked diffuse lymphoid depletion. The oesophageal lesions consisted of multifocal to coalescing granulomatous inflammation in the mucosa, with multifocal extension into the submucosa; intralesional macrophages also contained cytoplasmic organisms. The architecture of both adrenal glands was effaced by infiltrates of macrophages, plasma cells and neutrophils, as well as large foci of lytic necrosis and/or neutrophilic inflammation, which were often surrounded by abundant fibrous tissue. The adrenocortical cells and macrophages had numerous similar intracytoplasmic yeast-like organisms. There were fewer intracytoplasmic organisms in pneumocytes in the lungs, and they were occasionally found in phagocytic cells in the intestinal lamina propria, but were not associated with inflammation or other architectural changes in these tissues. The spleen had diffuse lymphoid depletion; numerous fibrin thrombi were present, FIG 1: Sectioned liver of a mara with disseminated histoplasmosis. Multifocal to coalescing whitish areas are present throughout the hepatic parenchyma