124 FUNGUS DISEASES OF MAN AND ANIMALS 



Occupational exposure may be important more because of the op- 

 portunity for repeated exposure than because it provides a single 

 exposure. For example, Aspergillus fumigatus is a common soil 

 fungus and everyone may have inhaled its conidia at times, yet 

 pulmonary aspergillosis in man is rare. It is said to occur most 

 often in France in people engaged in two occupations in which they 

 come into frequent and intimate contact with molded grain, namely, 

 those who feed pigeons in one case, and those who use meal in clean- 

 ing hair in the other. 



Clinical Course. The theoretical implications involved in the in- 

 itiation of these mycotic infections w^ere discussed by Henrici -^ in a 

 comparison of bacterial infections and certain of the deeper mycoses. 

 He pointed out a fundamental difference between the course of most 

 bacterial diseases and that of most of the deep mycoses. A typical 

 bacterial disease has a sudden onset with rapid resolution. A typical 

 mycosis, on the other hand, has an insidious onset. The develop- 

 ment of the disease is slow and frequently the infection spreads at 

 first only by extension to contiguous tissues. Even in generalized 

 mycoses with fatal termination this early stage of the disease may 

 be most important in respect to time if hematogenous dissemination 

 intervenes late in the disease. The primary lesion may be in the skin 

 or in the lungs, in either case spreading slowly by peripheral exten- 

 sion. When hematogenous or lymphatic dissemination finally occurs 

 the progress becomes rapid and death of the host may ensue. 



It should be pointed out that there are exceptions to this sequence. 

 Some bacterial diseases follow a slow chronic course and, conversely, 

 in some mycoses there is a rapid extension of the infection. The 

 most common form of coccidioidomycosis is an acute respiratory 

 disease which ordinarily follows a course not unlike that of a com- 

 mon cold or, in more severe cases, influenza. The disseminated form, 

 which is comparatively rare, may follow a rather rapid course to a 

 fatal termination in a few weeks or it may extend over a period of 

 years with very slow progression. Most of the mycetomas, with the 

 exception of the common form of actinomycosis, remain locahzed so 

 that widespread dissemination never occurs. Mycetoma of the foot, 

 for example, may have a duration of 15 or 20 years, yet never ex- 

 tend much above the ankle. Chromoblastomycosis has a similar slow 

 extension without dissemination, but satellite lesions arise by auto- 

 inoculation and influence the rate and extent of the involvement. 

 Sensitization. The importance of trauma in the initiation of some 

 of the mycoses, their slow initial progress, and their final rapid ac- 

 celeration suggest that the fungi causing them grow at first only on 



