Experimental cerebral zygomycosis in alloxan-diabetic rabbits: variation in virulence among zygomycetes

We investigated the potential of 33 different zygomycete isolates to cause cerebral disease following the intranasal instillation of their spores into ketotic rabbits with alloxan induced diabetes. The isolates represented six thermotolerant species of Rhizopus (R. arrhizus, R. chinensis, R. microsporus, R. oligosporus, R. oryzae, and R. rhizopodiformis), Absidia corymbifera, Cunninghamella bertholletiae, and Rhizomucor pusillus. All 13 isolates of the thermotolerant Rhizopus species proved to be cerebral pathogens as confirmed by culture and histopathology. One isolate of R. oligosporus and one isolate of R. rhizopodiformis, however, were less pathogenic than isolates of other Rhizopus species tested. Cerebral pathogenicity was noted with 2 of 5 isolates of Rh. pusillus and only 1 of 13 A. corymbifera isolates. Two thermotolerant C. bertholletiae cultures, recovered from human lesions, did not cause either cerebral or pulmonary disease in ketotic rabbits. The incidence of pulmonary zygomycosis caused by the isolates of the species of the four genera under study was as follows: Rhizomucor 24%, Rhizopus 22%, Absidia 9%, and Cunninghamella 0%. This study confirms the pathogenic potential of the thermotolerant species of Rhizopus to cause cerebral zygomycosis in ketotic diabetic rabbits and also revealed the potential of Rh. pusillus and A. corymbifera occasionally to cause the same disease in animals and humans.