Most fungus diseases of man, in comparison with bacterial and virus infections, are relatively non-contagious. Notable exceptions are some of the dermatophytoses such as favus and dermatophytosis but it is generally believed by most investigators that the reservoir of most species of pathogenic fungi is in the environment. The demonstration of a fungus in nature identical with a known pathogen is of more importance than simply completing the chain of events leading up to infection. A definite history of exposure to a certain environment may be of diagnostic significance in some cases and knowledge of the natural habitats of the more virulent pathogens may be of value in avoiding direct contact with potentially infectious material.
Reproduction of lesions in a susceptible animal is the only way in which a fungus isolated from nature can be proven unequivocably to be identical to a human pathogen.