CHAPTER VI 



FUNGUS DISEASES OF MAN AND ANIMALS— GENERAL 



CONSIDERATIONS 



Many different fungi have been described as causing various dis- 

 eases in man and animals. Some of these fungi are known only as 

 pathogens, and the diseases they cause, although sporadic and some- 

 times rare in occurrence, are fairly well known. Other fungi are 

 known both as pathogens associated with lesions in man and as 

 saprophytes in man's environment, and the circumstances under 

 which they sometimes become parasitic are not fully understood. 

 General discussions of the pathogenic fungi are to be found in many 

 review articles and textbooks.^"- "- ^^' ''• ^-' *^' '^ 



Etiology. In many cases the etiological relationship between mold 

 and disease can be proved by repeated demonstration of the fungus 

 in lesions, its isolation therefrom, production of an infection in ex- 

 perimentally infected animals, and recovery of the fungus from the 

 latter. There are numerous papers in the literature of medical my- 

 cology, however, in which this rigid proof of an etiological relation- 

 ship is lacking. The careless acceptance of an unproved mycotic 

 etiology frequently has led to error. Pinta, a tropical spirochetosis, 

 long thought to be a mycosis from which many different fungi w^ere 

 isolated, is an example of such a mistake. Many of the fungus dis- 

 eases are superficial lesions of the skin or mucous membranes. IMold 

 spores are ubiquitous and it is not at all surprising that they may 

 be cultivated frequently from exposed skin lesions, pus, and sputum. 

 Viable airborne spores of harmless saprophytes are often present in 

 pathological material, and they germinate and grow when the ma- 

 terial is planted upon culture media. The isolation of such a fungus 

 in culture may then be interpreted erroneously as evidence that it 

 was growing in and causing the lesion. One must develop a healthy 

 degree of scepticism with regard to the pathogenicity of fungi isolated 

 in culture from pathological material. 



In a general consideration of mycoses it is interesting to note that 

 fungi have been more successful as pathogens of plants than of 

 animals. The majority of plant diseases, whether of weeds, trees, 

 or commercially important crop plants, are caused by fungi, and 



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