Favus (Latin for "honeycomb"), a distinctive type of ringworm because of the characteristic scutula, was described by Celsus in the first century, A.D., in his De Medicina. He called it porrigo, a term also used by Pliny in his Historia Naturalis of the same century and by dermatologists up to the nineteenth century. It is now, however, obsolete, having been replaced by tinea (derived from Tineola, the generic name of the clothes moth). Celsus also described the inflammatory lesion of some forms of ringworm, which has been known ever since as the "kerion of Celsus."
Not until the mid-1840s was the mycotic nature of favus recognized by three independent workers: J. L. Schoenlein and Robert Remak in Berlin, and David Gruby in Paris. The latter also differentiated mi-crosporosis and the ectothrix and endothrix trichophytosis, which he showed to be caused by distinct fungi.
A period of mycologic confusion followed, complicated by the difficulty of determining the life histories of the pathogens (largely due to deficiencies in culture technique) and settling the question as to whether there was one ringworm fungus or many. Gruby's findings had been forgotten and had to be rediscovered during the 1890s by Raymond Sabour-aud, a famous Parisian dermatologist, who consolidated his researches in an impressive monograph published in 1910. Many ringworm fungi were described and classified variously according to the degree of emphasis placed by different workers on mycologic and clinical features. Some thousand different names had been proposed up to 1934 when C. W. Emmons, a mycologist by training, in the United States showed that, mycologically, the many species could be accommodated in the three genera: Mi-crosporum, Trichophyton, and Epidermophyton. Today the number of ringworm fungi accepted is of the order of 30. At first, only asexual spore states of these pathogens were known, but later sexual states were obtained, and evidence provided that dermatophytes are closely related to a group of predominantly soil fungi.
Two historical landmarks in the treatment of ringworm were the introduction of X-ray epilation for the therapy of head ringworm in the opening years of this century and the introduction of the antibiotic griseofulvin in 1958 as an orally administered antimycotic drug.
The geographic distribution of the ringworm fungi is interesting. In Sabouraud's time the distribution corresponded to that of interested dermatologists. Now the ringworm fungi of most countries have been surveyed, or at least sampled, so that a more accurate knowledge of their geographic distribution is available. Some, such as Trichophyton mentagrophytes (causing tinea pedis and so forth) and Epidermophyton floccosum (tinea cruris), occur worldwide.
Microsporum audouinii (tinea capitis; the classical cause of ringworm in children), which appears to have originated in Europe, is now endemic in North America. Although frequently introduced by European children to the tropics, it has never established itself there in the indigenous population. Likewise Trichophyton concentricum (tinea imbricata) is endemic in Southwest Asia and the South Sea islands, where it was first recorded by William Dampier in 1686 when circumnavigating the globe. It has other minor endemic centers in South America, and, although frequently seen in Europe on returning travelers, it has never become endemic there. By contrast, Trichophyton rubrum, believed to have been introduced into the United Kingdom by troops returning from the Boer War, is now widespread in north temperate regions.
In similar fashion, Trichophyton ferrugineum established itself in western parts of the Soviet Union, after being introduced by soldiers returning from the Far East. Classical favus in western Europe is caused by Trichophyton schoenleinii, but typically by Trichophyton violaceum in North Africa and the Mediterranean basin. Microsporum canis (tinea canis [cat and dog ringworm], tinea capitis, and tinea corporis), coextensive with cats and dogs as pets, has become endemic in New Zealand in feral cats. Human infections are also contracted by contact with ringworm in cattle (Trichophyton verru-cosum), horses, and other farm animals. Mi-crosporum gypseum (which could be considered as an opportunistic dermatophyte) has a worldwide distribution, the outbreaks in humans usually being sporadic, short-lived, and sometimes traceable to a group of people having access to the same soil in which the pathogen is an inhabitant.
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