The current role ofAspergillusandPenicilliumin human and animal health

Abstract

Aspergillus and Penicillium are ubiquitous fungi, usually found as saprophytes. Only a few species are considered to be important in human or animal disease. However, many otherwise benign species are supreme opportunists and have been found increasingly as invaders of the immuno- compromised. This paper first describes with a broad brush modern approaches to the classifi- cation of these genera, the reasons behind some name changes and the effective forces now act- ing to stabilize names. Recent taxonomic schemes are described. The taxonomy of pathogenic Aspergillus and Penicillium species is outlined, the subgenera where pathogens occur identified, and the question of why particular species are pathogens addressed. The significance of Aspergillus and Penicillium in mammalian disease is heightened by their production of potent mycotoxins. The importance of Aspergillusflavus and aflatoxins as a cause of human death in parts of Africa and Asia and the impact of ochratoxins, produced by Penicillium verrucosum, on human and animal health in Europe will be emphasized. Possible mycotoxin ingestion from spores poses a further health threat. Aspergillus and Penicillium are universal fungi. Species of both genera are found almost everywhere on earth. Penicillium is dominant in cooler climates, especially the cool temperate zones, while Aspergillus is more common in the tropics. The great majority of species are saprophytes, commonly or occasionally found in soil, decaying vegetation, seeds and grains. Only a few well known species have been recognized as important pathogens of humans or domestic animals. Aspergillus fumigatus was described by Fresenius in 1863 from the bronchi and alveoli of a great bustard. It has been recognized for most of this century as a pathogen, capable of invading the lungs of humans, animals and birds. Generally, high concentrations of spores are necessary for infection. Healthy animals are able to ward off infections, so that severe illness usually results only from long-term exposure. Several other Aspergillus species have a history of occasional pathogenicity. Aspergillus terreus is probably the most important. Although human infection is quite rare, the diseases caused are varied and not dissimilar to those caused by A. fumigatus (35). A. terreus has recently become notorious in Australia and parts of the USA as a cause of fatal systemic infections in German Shepherd dogs or, rarely, other breeds (12, 31, 39). Aspergillus niger has caused serious systemic infections, but is more commonly an aural invader. Aspergillusflavus is known as a rare cause of pulmonary disease in man, and is rather more common in birds. It has also been reported from skin, nails and occasionally systemic infections (4). A few other species including the 'Aspergillus glaucus group', Aspergillus restrictus and Aspergillus sydowii have been reported. However, infection by any of these species, with the exception of A. fumigatus and perhaps A. terreus, remains uncommon. Penicillium species have long, and rightly, been regarded as benign, and of little or no consequence as human or animal pathogens. Only a few papers deal with