Some Aspergillus species cause serious disease in humans and animals. The most common pathogenic species are A. fumigatus and A. flavus, which produces aflatoxin which is both a toxin and a carcinogen, and which can contaminate foods such as nuts. The most common species causing allergic disease are A. fumigatus and A. clavatus. Other species are important as agricultural pathogens. Aspergillus spp. cause disease on many grain crops, especially maize, and some variants synthesize mycotoxins, including aflatoxin. Aspergillus can cause neonatal infections.
A. fumigatus (the most common species) infections are primary pulmonary infections and can potentially become a rapidly necrotizing pneumonia with a potential to disseminate. The organism can be differentiated from other common mold infections based on the fact that it takes on a mold form both in the environment and in the host (unlike Candida albicans which is a dimorphic mold in the environment and a yeast in the body). Wikipedia