Pathology of Mucormycosis of Cane Toads in Australia

The gross and microscopic pathology of a fungal septicaemia caused by the zygomycete. Mucor amphibiorum in 27 free-ranging cane toads, Bufo marinus, in Australia is described. Seven of the 27 toads had clinical signs of illness when discovered and five of these seven were moribund. Multiple granulomas were found in many organs, and in massive infections granulomas tended to coalesce. Liver, spleen, kidneys, urinary bladder, heart and lung were most commonly involved, but granulomas also occurred in subcutaneous lymph spaces, skin, gastro-intestinal tract, voluntary muscle, bone, cranial cavity and the oral cavity. Single lesions appeared grossly as a lemon coloured nodule < or = 5 mm in diameter. Histologically, the primary lesion was a granuloma composed of multinucleate giant cells, macrophages, occasional lymphocytes and eosinophils surrounding the distinctive sphaerules of M. amphibiorum. Fibroblasts occurred in greater numbers at the periphery and collagen formed a dense fibrous capsule around some nodules. A less common lesion resembled a microabscess and consisted of mononuclear cells, neutrophils and eosinophils surrounded by macrophages. Many of the centrally placed mixed inflammatory cells appeared necrotic. This reaction appeared to be more acute. Both types of lesions sometimes occurred concurrently, but the latter was less common. The pattern of lesions and natural history of M. amphibiorum suggested that ingestion of contaminated soil may have been the route of infection.