U.D. Histologia i Anatomia Patològica, Facultat de Veterinària (UAB), Bellaterra, Barcelona, Spain
Abstract
Cryptococcosis is a deep mycosis of animals and human beings produced by Cryptococcus neoformans. This organism has two varieties that differ in epidemiologic and clinical aspects. Cryptococcus neoformans var neoformans has a worldwide distribution and has been isolated from bird droppings (mainly pigeon’s excreta), fruits, vegetables, soil, and sawdust of tropical trees.8,12 Cryptococcus neoformans var gattii mostly occurs in tropical and subtropical areas and has been isolated from red gums (Eucalyptus camaldulensis and E. tereticornis), although other environmental sources are also possible.8,15 In human beings, C. neoformans var neoformans usually affects immunocompromised hosts, whereas C. neoformans var gattii has been mostly isolated from immunocompetent hosts.16
Cryptococcosis has been sporadically reported in captive nonhuman primates,11,14 especially in Old World species.1,4,11 Cryptococcosis has been a remarkable problem in tree shrews (Tupaia tana and Tupaia minor) and elephant shrews (Macroscelides proboscides) at a zoo,20 and has also been documented in other captive colonies of tree shrews.7 There are two reports of spontaneous cryptococcosis in New World monkeys, one case in a squirrel monkey (Saimiri sciureus)14 and two cases in Geoffroy’s tamarins (Leontocebus geoffroyi).18 This paper describes the unusual pathologic findings of naturally occurring cryptococcosis in a common marmoset (Callithrix jacchus) involving the intestines and lymphatic vessels.
A 5-year-old female pet common marmoset was submitted for necropsy with a 1-month history of wasting. The day before death, it ate apparently well but had abdominal distension. It was housed in a greenhouse with a 7-year-old female. Red gums were not present in the enclosure. There were no pigeons or other birds in the greenhouse, but the animals escaped and potentially had access to free-living birds during some days before the death of this marmoset. The diet consisted of a cereal mix, fruits, bread, and mealworms.
At necropsy, diffuse hemorrhagic enteritis was observed. Sections of intestine, liver, kidneys, and brain were fixed in 10% buffered formalin and embedded in paraffin, cut at 5 µm, and routinely stained with hematoxylin and eosin. Special stains included periodic acid-Schiff (PAS) and Mayer’s mucicarmine (MM). Microscopically, the most prominent lesion consisted of transmural enteritis with full-thickness necrosis of the mucosa, fibrin deposition and infiltrates of mixed inflammatory cells (mainly neutrophils but also macrophages). There were numerous intralesional, spherical to oval, yeast-like cells that were 4–15 µm in diameter and surrounded by a wide clear halo. Their capsule stained positively with PAS and MM stains, which gave them a spinous aspect. Both single budding by a narrow base and chains of three or four budding yeasts were present. Intestinal and mesenteric lymphatic vessels had granulomas attached to their wall and lined by endothelium. These granulomas had intralesional yeasts and caused total or partial occlusion of the affected vessels. Other findings were focal granulomatous and necrotizing hepatitis without intralesional yeasts and with pleomorphic mononuclear cells, neutrophils and megakaryocytes within sinusoids; and marked mesangial nephropathy.
This is the second report of naturally occurring cryptococcosis in callitrichids. The diagnosis was based on the morphologic and staining features of the intralesional yeasts found in this marmoset. Cryptococcus is the only pathogenic fungus with a mucopolysaccharide capsule that stains positively with mucin stains such as MM.3
The marked involvement of the intestine in this case of spontaneous cryptococcosis in a marmoset is unusual, because the intestine is not a common target for cryptococcosis in animals and human beings.3 There were not either gross lesions in the lungs or microscopic findings in the brain. Pulmonary and central nervous system lesions are the most common findings in spontaneous cryptococcosis in nonhuman primates and human beings.1,3,11,14,16,20 Disseminated disease involving the lungs, spleen, intestine, and mesenteric lymph nodes was reported in two Geoffroy’s tamarins with spontaneous cryptococcosis; intestinal lesions consisted of “patchy denudation of the mucosa with networks of fibrils and scattered yeasts.”8 Takos subsequently failed to reproduce intestinal lesions in three Geoffroy’s tamarins inoculated orally with C. neoformans, yet it was isolated from the gastrointestinal tract of all tamarins.19 Cryptococcus neoformans has been sporadically detected as an opportunistic enteric pathogen in acquired immunodeficiency syndrome (AIDS) patients with diarrhea.10
Inhalation of contaminated dust is expected to occur in most cases of cryptococcosis, and it is followed by pulmonary involvement with subsequent hematogenous spread that causes disseminated infection with a marked predilection for the brain.3,12 However, other points of entry, such as the skin and gastrointestinal tract, may also play a role in some cases.3,13,19 According to the pathologic findings in this marmoset, infection was probably acquired by the oral route. The source of infection could not be identified. There was no evidence for the involvement of red gums in this case. However, C. neoformans var gattii may have other, yet unrecognized sources.5,15 Cryptococcus neoformans var gattii has been isolated from domestic species such as horses, cats and dogs,9,13 and also zoo animals such as koalas and a kiwi with evidence of involvement of Eucalyptus trees in the transmission.6,9,17
The necrotizing and suppurative aspect of the intestinal mucosal lesions in this marmoset is characteristic of the initial response to C. neoformans in healthy, uncompromised individuals.3 These findings suggest that cryptococcosis might occur as a primary intestinal infection in callitrichids. However, concurrent or underlying intestinal or systemic diseases in this marmoset could not be ruled out. The immunologic status of this marmoset is unknown, and the only concurrent disease identified at necropsy was marked mesangial nephropathy, which is a common finding in captive callitrichids.2
Intravascular granulomas with intralesional cryptococci similar to those seen in the intestinal lymphatic vessels of this marmoset have been described in rodents experimentally inoculated intravenously with C. neoformans.21
Acknowledgments
The authors are grateful for assistance with histologic studies provided by Pere Losada and Blanca Pérez. We appreciate the helpful comments on this case by Dr. Manfred Brack (Deutsches Primatenzentrum, Göttingen, Germany) and Dr. Richard Montali (National Zoological Park, Washington D.C., USA).
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