Fungi (plural of fungus) are a group of micro-organisms that are members of their own kingdom, neither plant nor animal. Fungi are common in the environment, living in the soil, on plants and trees, and on many indoor surfaces as well as on human skin. Of the approximately 1.5 million different species of fungi found on Earth, only about 300 are known to cause illness and make people sick.1
Under usual conditions, fungal infections are rare. The immune system protects against these infections. Normal components of the immune system that assist the body in preventing fungal organisms from spreading and causing invasive infections include:
- Mucosal membranes – intact lining of the mouth and gut
- White blood cells – cells in the blood stream and tissue which fight germs
- Antibodies – sticky proteins made by lymphocytes which target and attach to germs and assist in elimination of these germs
- Normal bacteria that live on the mucous membranes and prevent fungal organisms from taking hold and growing
Many treatments, disease conditions or other circumstances weaken components of the immune system and increase the risk of developing serious infections. 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. When fungal organisms enter the body and the immune system is compromised these fungi grow, spread and invade into tissue and spread locally. Some organisms, especially yeast and some molds, can invade the blood vessels and cause infection in the bloodstream and distant organs.
Factors that Increase Risks for Invasive Fungal Infections
- Cancer chemotherapy medications, especially higher doses that cause low white blood counts
- Radiation treatments
- Immune suppressants such as anti-rejection medicines
- Immune suppressants that treat inflammatory conditions (arthritis, etc.)
- Broad spectrum antibiotic used for > 4-7 days
- Leukemia, Lymphoma
- Immune deficiency syndromes – acquired or inherited
- Burns (extensive)
- Disorders of white blood cells that impair production or function
- Blunt abdominal trauma
- Sepsis (severe, life-threatening infection in the blood stream and organs)
- Organ transplant
- Stem cell transplantation
- Presence of an indwelling central venous catheter or device
Fungal Infections- Types
Fungal infections may occur in people with normal immune systems and, though uncommon, can be very serious. In situations when the immune system is weakened these infections are termed opportunistic (i.e., the organisms take advantage of the immune system failure and become invasive). Opportunistic fungal infections can be very aggressive, spreading quickly to other organs and often leading to death. Typical opportunistic fungal infections include:
- Yeast – Candidiasis, Cryptococcosis
- Zygomycoses (Mucormycoses)
Invasive candidiasis is an infection caused by a yeast called Candida that normally lives in the gastrointestinal tract and on the skin without causing any problems. In patients with compromised immune systems Candida species can cause disease along mucous membranes, blood stream infections, infections in organs (live, kidney, spleen, etc.) and CNS infections. Morbidity and mortality rates are high, and therapy is often, inadequate
Cryptococcus is a fungal, yeast organism that lives in the soil and can also be spread by birds through feces. Infections in humans are rare and usually occur in patients with compromised immune systems. Patients with AIDS, in particular, are especially susceptible to this type of infection.
In the United States, cryptococcosis meningitis is thought to be less common, largely because of earlier diagnosis of HIV and earlier initiation of antiretroviral therapy, factors that help keep people with HIV from reaching the stage when their immune systems leave them most vulnerable to fungal infections.2,3
Aspergillus is a common mold that lives indoors and outdoors which causes an infection called aspergillosis. Because Aspergillus is usually acquired through the air, people with weakened immune systems are susceptible to infections in the lungs (more commonly) and the nasal passages (less commonly), but infection can also spread to other parts of the body.4 Aspergillus infections are serious, life-threatening, and often fatal infections in patients with compromised immune systems.
Aspergillus is hard to diagnose since symptoms are not specific. X-rays and CT scans are helpful, but not sufficient most of the time for proof. Biopsy of infected tissue with pathology proof or growth of the organism in tissue is confirmatory. However, many patients are too sick to have an invasive biopsy and though new blood tests are helpful, they provide circumstantial evidence. Treatment is based on proof by culture or biopsy, but many clinicians will treat based on suspicion or a set of symptoms and signs that support the likelihood. Patients with weakened immune systems and proven aspergillosis have a very high (>50%) death rate from infection so early detection and treatment have become the standard recommendation.
Zygomycoses and other molds (Fusariosis, etc.)
Zygomycosis (sometimes called mucormycosis) is a rare but serious fungal infection caused by a group of molds called zygomycetes (also known as mucormycetes) that are often found in soil and decaying organic matter such as leaves, compost piles, or rotten wood. Although zygomycosis can form in nearly any part of the body, it most commonly affects the lungs or sinuses of people with weakened immune systems, such as those who have had an organ or stem cell transplant, or those with uncontrolled diabetes.5 However, because symptoms are difficult to distinguish from more common mold infections (Aspergillus), diagnosis can be difficult unless a positive culture or tissue is obtained.
Fusarium is a fungus that commonly lives in soil and on plants. Infections in patients with weakened immune systems can involve mucosal membranes and lungs (similar to other molds) but can also spread to the blood stream, skin, and to the retina in the eyes, similar to yeasts. Diagnosis can be made from culture from a normally sterile site such as blood or tissue.