The occurrence of pathogenic fungi in the normal human body
Resca, Helen Gertrude
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Each region of the body has its own natural micro-organisms, which constitute the normal flora of that region. Among the organisms present are bacteria and higher fungi. Pathogenic fungi in the normal flora regarded as important because of the threat which they offer to the health of the body. Under the proper circumstances, these pathogens can invade the tissues, setting up an infection. Fungus diseases which terminate fatally are numerically important, although they are responsible for only 0.03% of deaths in the United States in any year. Non-fatal fungus diseases are very prevalent, being almost as common as any bacterial diseases. Notable among these is coccidioidomycosis, acquired by 75 to 97% of the children on Indian reservations in Arizona. Tinea capitis is now referred to as an epidemic communicable disease. Dermatophytosis of the feet is also an ever-present mycosis which does not result in death. Fungus infections are, for the most part, endogenous origin. For instance, actinomycosis is not transmitted from one human to another, nor from animal to man. The causative organism, Actinomyces bovis, does not exist outside the body, so the infection must be endogenous. In the Ebers Papyrus, written about 1500 B.C., the first reference to fungi is found. But it was not until 1683 A.D., when Leeuwenhoek developed his lenses, that microorganisms were seen for the first time. Suspicion that microbes caused disease was harbored by Fracastor in 1543. The hair and scalp, although popularly believed to be free from living organisms; harbors many fungi among which is the pathogenic Pityrosporon ovale. Skin, even though is has been scrubbed clean, is never entirely free from bacteria. Monilia albicans, the etiologic agent of moniliasis, is found on normal skin. Cryptococci and mycodermata, responsible for cryptococcosis and geotrichosis, respectively, have been isolated from the skin and nails of individuals. Ordinary cleansing of the skin, which insures the proper action of the germicidal power, is sufficient to keep the pathogens found normally on the skin in check. However, a mere break in the skin, or excessive moistening of this protective barrier is in many instances, sufficient for pathogens to enter, and gain a foothold, to cause an infection. The feet provide a favorable environment for fungus growth, as in indicated by the high incidence of dermatophytoses of the feet. Men seem to be more susceptible to mycosis of the feet, according to figures presented. However, this has been shown to be due to the gymnasium habits and the mobilization of men, and not a sex difference. Some people must be more susceptible than others, though, since familial and conjugal transmission of ringworm of the groin is so rare that mycologists are convinced of the endogenous origin of this mycosis. The ears do not contain the agents of otomycosis, but these organisms, belonging mainly in the genus Aspergillus, are found on normal skin. Injury to the external auditory canal by the unskilled removal of excess cerumen has resulted in otitis. The external genitalia contain no fungi, except for the vagina, which has a varied flora. Monilia albicans is found there constantly. The internal genitalia are sterile. The eyes and lungs harbor no fungi, nor do the accessory digestive organs, such as the liver, pancreas, and so on. The mouth, however, contains a host of organisms; the most important of the fungi which are found frequently in the normal mouth, is the patnogenic Monilia albicans, which causes thrush or oral moniliasis. In an original investigation by the writer, it was found that of the 50 subjects were positive for yeastlike fungi, most of which were Monilia albicans. The organisms were tested for their pathogenicity to mice by intraperitoneal injections. Of the 17 cultures, 5 proved fatal to the mice. Some of the animals which lived looked unhealthy for a few days. Thus a variable degree of pathogenicity is indicated. M. albicans may also be associated with dental caries, because of the production of acid when it ferments carbohydrates, and because it has been found in a significantly high percentage of caries cases as contrasted with a low percentage of non-caries cases. No significant correlation between the presence of yeastlike fungi and caries experience in the last two years was noted in the present study. A slight tendency for extensive caries involvement to be associated with yeasts was seen, but the difference was not statistically significant. Consideration of the problem of dental caries and its etiological factors reveals that no one factor can be named as the sole agent of caries. Constitution, environment, diet, mouth flora---all of these may play a part. Since the time of Hippocrates, theories which attempt to explain caries have been put forth. The disease existed as long ago as 2800 B.C., for the remains of people buried about that time were examined and found to have as high an incidence of caries as the people of Europe in 1930. Diet is believed responsible for the caries prevalence among people of today. Over 95% of human beings are believed to be afflicted with this disease. Tropical inhabitants who have incorporated the soft diet of the whtte ra.ces have acquired also the high incidence of caries. Fracastor, as early as 1543 A.D., conceived of living organisms as the cause of caries. Today the belief is that a combination of factors is responsible. Bacteria and fungi ferment carbohydrates, producing acid in susceptible teeth. If the teeth are constitutionally sound, or are protected by a high fluorine content, thus being rendered less soluble in acid the presence of the acid-producing organisms makes no difference to the individual. However, if the calcium of the mother is insufficient for sound tooth formation in the child, and the drinking water does not contain fluorine to strengthen the teeth against decalcification, and the mouth contains acid-producing organisms, then the child is quite susceptible to caries. The nose contains a variable group of organisms, so that it has been said that a "normal flora" as such cannot be described. However, Saccharomyces has been named as a pathogenic fungus found in the nose. Other fungi are present, but their pathogenicity is not stated. The acidity of the stomach keeps that organ practically sterile, although many organisms are swallowed. Surviving bacteria and fungi descend into the intestines, and, finding those regions more amenable to their growth and multiplication, occur there in great numbers. Among the organisms in the alimentary canal are Monilia albicans, cryptococci, and mycodermata. In the lower, more alkaline region of the intestines, Actinomyces bovis is found, often giving rise to cecal actinomycosis. Thus, it is evident that the body harbors on its skin and mucous membranes, especially on the latter, several types of pathogenic fungi. These organisms are able to attack the host, but only when his resistance to disease is lowered. At other times, the microbes exist as saprophytes, doing no harm to the host.
Thesis (M.A.)--Boston University