Mycotic Disease

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Mycotic Disease

Introduction

Disease History, Characteristics, and Transmission

Scope and Distribution

Treatment and Prevention

Impacts and Issues

BIBLIOGRAPHY

Introduction

Mycotic diseases are caused by fungi, which are present in many forms in the environment. Many fungi are found in soil and are transmitted to humans either via cuts in the skin or by inhalation of the spores or cells of the fungi. Fungi can also inhabit moist environments, such as damp clothing, shoes, and showers. Transmission occurs when a person's skin comes in contact with the fungi. Other fungi may already be present in the human body at a certain population level (this is termed colonization) and cause infection only when the fungal population grows. An example of this is the common fungal infection of the mouth known as thrush.

Symptoms of a fungal disease can range from skin irritations to organ damage, such as lung disease. Fungi are characterized by the area of the body that they affect. Some fungi affect the outer layer of the skin, while others affect the cutaneous and subcutaneous layers of the skin. Furthermore, some fungi develop first in the lungs before spreading to other regions, while other fungi are opportunistic and develop wherever they can. Fungal infections are generally treated with antifungal drugs taken internally or applied externally. However, many of these drugs are toxic and cause side effects. In addition, some fungi are beginning to develop resistance to treatment making it difficult to eradicate an infection.

WORDS TO KNOW

COLONIZATION: Colonization is the process of occupation and increase in number of microorganisms at a specific site.

CUTANEOUS: Pertaining to the skin.

IMMUNOCOMPROMISED: A reduction of the ability of the immune system to recognize and respond to the presence of foreign material.

OPPORTUNISTIC INFECTION: An opportunistic infection is so named because it occurs in people whose immune systems are diminished or are not functioning normally; such infections are opportunistic insofar as the infectious agents take advantage of their hosts’ compromised immune systems and invade to cause disease.

SPORE: A dormant form assumed by some bacteria, such as anthrax, that enable the bacterium to survive high temperatures, dryness, and lack of nourishment for long periods of time. Under proper conditions, the spore may revert to the actively multiplying form of the bacteria.

Disease History, Characteristics, and Transmission

Different types of fungi affect different regions of the body and mycotic diseases are characterized according to the region being affected. Superficial infections involve the outer layers of the skin and hair; cutaneous infections involve the epidermis, hair and nails; and subcutaneous infections involve the dermis, subcutaneous tissues, and muscle. There are also systemic infections that are caused by either primary fungi or opportunistic fungi. Primary fungi originate in the lungs before spreading infection to other organ systems. Opportunistic fungi infect anywhere in the body. Opportunistic fungal infections tend to occur most commonly in people with a suppressed or weakened immune system, when their health is already compromised.

Fungal infections cause a range of symptoms depending on the body region they infect. Cutaneous (skin) infections such as tinea, which is a disease of the skin, tend to result in itchy, peeling skin, sometimes with pus or inflamed areas. These symptoms are usually not life threatening, but can cause discomfort and irritation. Subcutaneous infections tend to occur when fungi enter under the skin and forms lesions as they grow. Systemic fungi originate in the lungs and eventually spread to other organs, potentially causing tissue damage, ulcers, and pulmonary symptoms. Opportunistic fungi can potentially cause disease in any region of the body.

Humans develop fungal infections when they come in contact with a fungus. Some fungi are present in the soil. Therefore, when soil is disturbed, for example, during an earthquake or while gardening, fungal spores can become airborne and be inhaled. The fungi can then cause infection. Other fungi thrive in moist, dark conditions. Therefore, moist clothing, shoes, or certain rooms, such as bathrooms, can harbor fungi. When humans come in contact with these fungi, infection can occur. One example is athlete's foot, a type of tinea. Often the fungi responsible for this disease will develop in shoes or in showers and can be spread from these sources. One common fungi from the genus Candida gives rise to thrush, a common infection that causes an itchy rash. This infection can occur in the genital area, in the mouth, or in the bloodstream. The fungus is already present in humans in small amounts, and infection occurs when the fungus grows out of control, often in response to a hormonal imbalance.

Scope and Distribution

There are a range of mycotic diseases worldwide. A common fungal infection is tinea, which refers to cutaneous infection of various parts of the body. This infection is common on the feet where it is known as athlete's foot, and in the crotch where it is known as jock itch. Both of these infections can be present in males and females and spread of this disease is facilitated by shared locker rooms or showers where people tend to walk around barefoot.

Some infections occur more commonly in certain people, or people with certain conditions. Genital thrush, which is caused by the fungus Candida, is very common in women, and is also more common during pregnancy, in women with diabetes mellitus, or in women using broadspectrum antibiotics or corticosteroid medications.

Immunocompromised people appear to be at a significantly greater risk of developing fungal infections. Even fungi that normally do not cause infections in healthy people have been found to cause illness in people with compromised immune systems, such as are caused by certain conditions including cancer, diabetes, or AIDS. In addition, some fungal infections can cause more severe symptoms when they develop in these people. For example, HIV-infected people may develop severe pulmonary disease leading to death following infection by the fungus Coccidioides immitis. Other factors such as stress can also increase the likelihood of a fungal infection.

Fungal infections occur worldwide, although specific infections may be found only in some locations. Cryptococcosis, a fungal infection that causes potentially fatal meningitis, can be found in soils worldwide. Coccodioidomycosis on the other hand is endemic to areas in the United States, Mexico, and South America. The potential to pick up a fungal infection depends on whether it is present within the country, and whether living or working conditions promote the growth and transmission of the fungus. Sporotrichosis occurs in hay and is transferred via cuts in the skin. Therefore, individuals, such as farmers, who handle hay on a regular basis are more susceptible to this fungal infection.

IN CONTEXT: FUNGI

Fungi play an essential role in breaking down organic matter and thereby allowing nutrients to be recycled in nature. As such, they are important decomposers and without them living communities would become buried in their own waste. Some fungi, the saprobes, get their nutrients from nonliving organic matter, such as dead plants and animal wastes, clothing, paper, leather, and other materials. Others, the parasites, obtain nutrients from the tissues of living organisms. Both types of fungi obtain nutrients by secreting enzymes from their cells that break down large organic molecules into smaller components. The fungi cells can then absorb the nutrients.

Although the term fungus invokes unpleasant images and can be a source of disease, fungi are also a source of antibiotics, vitamins, and industrial chemicals. Yeast, a form of fungi, is used to ferment bread and alcoholic beverages.

In addition to human diseases fungi also cause food spoilage, wheat and corn diseases, and, perhaps most well known, the Irish potato famine of 1843–1847 (caused by the fungus Phytophthora infestans), which contributed to the deaths of 250,000 people in Ireland.

Treatment and Prevention

Fungal infections are generally treated using antifungal drugs. These drugs can be taken orally, via the genital tract, or applied externally. Some common antifungal treatments contain azole derivatives and actively prevent the fungus from producing ergosterol. Ergosterol is used by fungal cells to produce a cell membrane, and lack of ergosterol results in cell death and death of the fungus. However, many treatments for fungal infections are extremely toxic and can cause serious side effects, if used incorrectly.

As no vaccines are available for mycotic diseases, avoidance or removal of fungi is the best method of prevention. Maintaining high sanitary standards can help avoid coming into contact with potentially dangerous fungi. For example, wearing bath shoes in communal showers, avoiding wearing moist clothes, or drying damp shoes can all help prevent contracting the fungus responsible for athlete's foot. Thorough cleaning of contaminated items, such as clothing and bedclothes, using hot water and detergent may remove the fungi from these items, and prevent infection.

For fungi that can be transmitted via airborne spores or cells, avoiding areas in which soil has been disturbed will help minimize contact with fungal spores. For example, in an area where soil fungi are a potential problem, wearing a facemask following an earthquake may help prevent infection. Wearing gloves can also provide protection against soil fungi that are transmitted via cuts in the skin. This is one way to avoid sporotrichosis, which is caused by fungi present in bales of hay or other plant materials that are often harvested and used by humans.

Impacts and Issues

The U.S. Centers for Disease Control and Prevention, Division of Bacterial and Mycotic Diseases reports that mycotic infections are becoming an increasing risk to the public health. Immunocompromised people, such as cancer patients, HIV-infected individuals, and people with diseases such as diabetes, are at a high risk of developing fungal infections due to opportunistic fungi, such as aspergillosis, candidiasis, and cryptococcosis. Furthermore, new forms of old fungal infections, such as coccidioidomycosis, are occurring in these patients. In addition, previously harmless fungi, which normally grow in rotting food, soil, or plants, are now causing potentially fatal or debilitating infections in immunocompromised individuals.

Another issue of significant concern is the development of resistance to antifungal drugs by certain strains of fungi. This has occurred in response to the use of antifungal treatments for fungal infections. For example, in some people, Candida fungi, which cause thrush, have developed resistance to the antifungal treatments used to eradicate this infection. Therefore, fewer treatment options are available as the fungi become resistant to the certain drugs.

The rise in the number of mycotic infections has led to a increased research into the control and prevention of fungal diseases. Mycotic disease research involves determining the cause of outbreaks, risk of outbreaks, outbreak trends, and methods of control.

See AlsoAntibiotic Resistance; Aspergillosis; Blastomycosis; Candidiasis; Coccidioidomycosis;

Cryptococcus neoformans Infection; Histoplasmosis; Opportunistic Infection; Ringworm; Sporotrichosis.

BIBLIOGRAPHY

Books

Dismukes, W. E., P.G. Pappas, and J.D. Sobel. Clinical Mycology. New York: Oxford University Press, 2003.

Howard, D.H. Pathogenic Fungi in Humans and Animals. New York: Marcel Dekker, 2003.

Web Sites

Centers for Disease Control and Prevention. “WHO Collaborating Center for the Mycoses.” February 5, 2007. <http://www.cdc.gov/ncidod/dbmd/mdb/index.htm> (accessed March 6, 2007).

Southern Illinois University. “Mycotic Infections.” <http://www.cehs.siu.edu/fix/medmicro/mycotic.htm> (accessed March 6, 2007).