Immunofluorescence staining of hyphae in the histopathological diagnosis of mycoses in cattle.

An immunofluorescence staining system was developed for the identification of mycelial fungi causing systemic mycoses in cattle. Antisera to Absidia corymbifera, Aspergillus fumigatus, Aspergillus flavus, and Aspergillus niger were raised in rabbits. Tissue sections of experimentally infected mice were used to determine the specificity of immune staining with antisera that had been absorbed with heterologous antigens. When 46 lesions from 22 cattle with systemic mycosis were studied, the infecting agent could be classified as a zygomycete, possibly A. corymbifera, in 18 lesions (15 cattle), A. fumigatus in 10 lesions (7 cattle) and both a zygomycete and A. fumigatus in a single lesion from one animal. Diagnosis was established by light microscopy in 13 (72%) of the 18 lesions classified as zygomycosis. Conversely, a dual infection with both a zygomycete and an Aspergillus species was suspected on the basis of morphology in nine of the 10 lesions reacting exclusively and uniformly with anti-A. fumigatus antiserum. A. fumigatus may be a more frequent aetiological agent of systemic mycosis in cattle than hitherto recognized on the basis of light microscopy and mycological culture.