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Overview of Fungal Infections

By

Sanjay G. Revankar

, MD, Wayne State University School of Medicine

Last full review/revision Apr 2021
CLICK HERE FOR THE PROFESSONAL VERSION
Topic Resources

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.

Did You Know...

  • Fungi are their own kingdom. They are neither plants nor animals.

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

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 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 (see Opportunistic fungal infections Opportunistic fungal infections 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... read more ).

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

Opportunistic fungal infections can be very aggressive, spreading quickly to other organs and often leading to death.

Risk Factors for Developing Opportunistic Fungal Infections

Use of drugs that suppress the immune system

  • Cancer chemotherapy drugs

  • Corticosteroids

  • Drugs to prevent rejection of an organ transplant, such as azathioprine, methotrexate, and cyclosporine

  • Tumor necrosis factor inhibitors (used to treat rheumatoid arthritis and related disorders)

Disorders

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:

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 Culture of Microorganisms Infectious diseases are caused by microorganisms, such as bacteria, viruses, fungi, and parasites. Doctors suspect an infection based on the person's symptoms, physical examination results,... read more ) 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 (a bronchoscope Bronchoscopy Bronchoscopy is a direct visual examination of the voice box (larynx) and airways through a viewing tube (a bronchoscope). A bronchoscope has a camera at the end that allows a doctor to look... read more Bronchoscopy ) 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 Needle Biopsy of the Pleura or Lung A needle biopsy is a procedure in which a biopsy needle is inserted into the lung or through the membrane surrounding the lung (pleura) and is used to remove a piece of tissue for examination... read more or surgery is necessary to obtain a sample.

Treatment of Fungal Infections

  • Antifungal drugs

Several drugs effective against fungal infections are available, but the structure and chemical makeup of fungi make them difficult to kill.

Antifungal drugs may be applied directly to a fungal infection of the skin or other surface, such as the vagina or inside of the mouth. Antifungal drugs may also be taken by mouth or injected when needed to treat more serious infections. For serious infections, several months of treatment are often needed.

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