 |
In evolutionary terms, fungi are ancient. By 300 million years ago, all forms of fungi existed, and there is undisputed evidence of fungal fossils from 400 to 440 million years ago. Some estimates put the number of species at nearly 2.5 million, and well over 100,000 varieties have been categorized. In general, fungi are free-living in nature and are not dependent on humans or animals for their survival. They mostly have very limited pathogenicity, with few invasive properties. Prehistoric man must have coexisted with fungi for millions of years, and they probably never posed a serious threat to health. Until the latter decades of the 20th century, modern man would have been more familiar with the positive attributes of fungi: edible mushrooms and truffles; the yeast-producing bubbles in beer, champagne, and bread; and the discovery of one of the first antibiotics from the mould Penicillium notatum.
Fewer than 200 species have been associated with human disease and only a handful of these are capable of causing significant disease in otherwise healthy individuals. Pathology textbooks in the first half of the 20th century devoted little space to diseases due to fungi, restricting discussion to infections acquired from environmental sites in nature where the fungus grows as a saprophyte, or to superficial infections of skin, nails, and mucous membranes.
However, recent years have seen an increase in morbidity and mortality associated with the appearance of new or previously very rare mycoses. Systemic infection with organisms such as Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans indicates an unprecedented change in the status quo of the relationship of the fungi to man.
True pathogens are few, and the majority of infected individuals are located in regions endemic for the fungus; infection results from inhalation of conidia (sometimes mistakenly called spores) released into the atmosphere. Examples in the United States include infections with Histoplasma capsulatum along the Mississippi River Valley, Coccidioides immitis in the Southwest, and Blastomyces dermatitidis in northern, central, and southeastern states.
The majority of people living in areas with endemic disease have been infected at some point. In most individuals, inhaling conidia causes a mild and transient chest infection with flu-like symptoms; other symptoms include rash and, rarely, arthritis. Dissemination to areas of the reticuloendothelial system occurs in most people infected with histoplasmosis, but this is generally asymptomatic. The infection normally resolves without treatment, although full recovery can take several months. Granulomas visible on chest X-ray and splenic calcification reflect healing of the infection. Until the 1980s, the incidence of disseminated disease remained low. However, in the last 20 years, the number of patients with significant morbidity and mortality related to these endemic organisms has increased. Population movements and climate may be important factors in localized outbreaks. For example, the number of reported cases of coccidioidomycosis in Arizona increased from 7.0 cases per 100,000 population in 1990 to 14.9 cases per 100,000 population in 1995 [1]. The disease disproportionately affected persons aged greater than 65 years. During this period, many older people moved to the state from areas where coccidioidomycosis was not endemic, and this factor together with underlying health conditions in this population may have contributed to the dramatic increase in infection rate. Severe drought followed by heavy rainfall was identified as a possible factor associated with an epidemic of coccidioidomycosis in California [2]. Disseminated coccidioidomycosis and histoplasmosis are also increasing in persons with AIDS, not only in patients living in endemic areas but also in those living elsewhere, indicating that reappearance of prior infection can occur in this setting [3].
Course Number: V035B.043001
This CME Expires on July 1, 2003; no tests will be accepted after this date.
This course is accredited by
The University of Pittsburgh School of Medicine, Center for Continuing Education
|
|
