https://www.merckmanuals.com/home/infections/fungal-infections/overview-of-fungal-infections
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Fungi are neither plants nor animals. They were once thought to be plants but are now classified as their own kingdom. Some fungi cause infections in people.
- Because fungal spores are often present in the air or in the soil, fungal infections usually begin in the lungs or on the skin.
- Fungal infections are rarely serious unless the immune system is weakened, usually by drugs or medical disorders.
- Fungal infections usually progress slowly.
- Antifungal drugs may be applied directly to the infected site or, if the infection is serious, taken by mouth or injected.
Fungi can grow in two forms:
- Yeasts: Single round cells
- Molds: Many cells forming long, thin threads called hyphae
Some fungi go through both forms during their life cycle.
Fungi often grow in soil and decaying plant material. Many fungi, including bread molds and mushrooms, can be seen with the naked eye.
Fungi reproduce by spreading microscopic spores. These spores are often present in the air and soil, where they can be inhaled or come into contact with the surfaces of the body, primarily the skin. Consequently, fungal infections usually begin in the lungs or on the skin.
Of the wide variety of spores that land on the skin or are inhaled into the lungs, most types do not cause infection. A few types cause infection only in people who have one of the following:
- A weakened immune system
- Foreign material, including medical devices (such as an artificial joint or heart valve), in their body
The immune system may be weakened when people take drugs that suppress the immune system (immunosuppressants), such as chemotherapy drugs or drugs used to prevent rejection of an organ transplant, or when they have a disorder that causes immunodeficiency, such as AIDS. People who spend many days in an intensive care unit can develop a weakened immune system because of medical procedures, underlying disorders, undernutrition, or a combination.
Except for some superficial skin infections, fungal infections are rarely passed from one person to another.
Fungal infections are either
Fungal infections can affect only one area of the body (localized) or many areas of the body (systemic).
Localized fungal infections affect only one area of the body. They typically affect the skin and nails, vagina, or mouth and may occur in people who have a normal or weakened immune system.
Localized fungal infections sometimes occur when the normal balances that keep fungi in check are upset. For example, certain types of fungi (such as Candida) are normally present on body surfaces or in the intestine. The bacteria normally present in the digestive tract and vagina limit the growth of these fungi in those areas. When people take antibiotics, the helpful bacteria can be killed, allowing the fungi to grow unchecked. The resulting overgrowth of fungi can cause symptoms, which are usually mild. As the bacteria grow back, the balance is restored, and the problem usually resolves.
Systemic fungal infections affect organs such as the lungs, eyes, liver, and brain and also can affect the skin. They typically occur in people who have a weakened immune system.
Opportunistic fungal infections
Opportunistic fungal infections take advantage of a weakened immune system. Thus, they usually occur in people with a weakened immune system, such as those with AIDS or those taking drugs that suppress the immune system. Opportunistic fungal infections occur worldwide. Typical opportunistic fungal infections include
- Aspergillosis
- Candidiasis
- Mucormycosis
Opportunistic fungal infections can be very aggressive, spreading quickly to other organs and often leading to death.
Primary fungal infections
Primary fungal infections can occur in people with a normal immune system, sometimes with serious consequences. These infections usually occur after people inhale fungal spores, which can cause pneumonia to develop in the lungs as the first sign of infection.
Certain primary fungal infections are more common in certain geographic areas, as in the following examples:
- Histoplasmosis is especially common in the Ohio and Mississippi River valleys, central New York, and Texas in the United States. It also occurs in parts of Central and South America, Africa, Asia, and Australia.
- Blastomycosis is particularly common in the eastern and central United States. It also occurs in Africa and in the Saint Lawrence River valley of Canada.
- Coccidioidomycosis occurs almost exclusively in the Southwest, Washington, and the central valley of California in the United States and in northern Mexico and Central and South America.
- Paracoccidioidomycosis occurs mainly in certain parts South and Central America.
Travelers can start to develop symptoms any time after returning from these areas.
Because many primary fungal infections develop slowly, months or years may pass before people seek medical attention. Typically, if the immune system is normal, fungal infections do not spread to organs deep in the body.
Diagnosis of Fungal Infections
- Culture and examination of a sample
- Blood tests
If doctors suspect a primary fungal infection, they ask people questions that can help with the diagnosis, such as the following:
- Where they have traveled and lived to determine whether they may have been exposed to certain fungi, perhaps years previously
- Whether they are taking any drugs that can suppress the immune system
- Whether they have a disorder than weakens the immune system
Doctors then take a sample to be grown in a laboratory (cultured) and examined under a microscope. The sample may be sputum or blood, but, occasionally, doctors must take a sample from the lungs. To take a sample from the lungs, doctors insert a flexible viewing tube (bronchoscope) through the mouth and into the airways. Fluid is squirted through the tube, then suctioned back into the tube, bringing cells and any fungi (or other microorganisms) with it. Sometimes biopsy or surgery is necessary to obtain a sample.
If the diagnosis is unclear, blood tests may be done. These tests check for antibodies (which are produced by the person's immune system in response to foreign substances, including fungi), antigens (molecules from foreign substances that can trigger an immune response in the body), or other evidence of the fungi.
Tests that detect genetic material in microorganisms are also done for some fungal infections.
