What are Fusarium?

Definition

Fusarium are widely distributed plant pathogens
that can cause skin, wound, lung, and invasive infections in humans.
Fusarium also produce many allergens and mycotoxins.

Natural Habitat and Features

Fusarium are widely distributed fungi (molds) that grow on a variety of substrates, including plants (and
their roots), food, soil, and wet, indoor environments. Fusarium
tend to produce fast-growing, woolly to cottony, flat-spreading cultures and come
in many colors, including white, gray, red, cinnamon, pink, yellow, and
purple.

Fusarium are present mainly in the anamorphic or asexual phase. Some Fusarium species also have a telemorphic phase and produce ascospores. Some of the more common Fusarium ascospore forms are Gibberella avenacea, intricans, zea, subglutinans, and moniformis; these are the telomorphic forms of F. avenaceum, equiseti, graminearum, subglutinans, and verticilloides, respectively. Haematonectria spp.are teleomorphic forms of F. solani.

Fusarium often produce two types of asexual spores, including macroconidia, borne on long sickle or banana-shaped structures, and microconidia, borne on chains. Many species of Fusarium also produce chlamydospores, which are thick-walled resting spores that can survive long periods in unfavorable conditions, such as drought.

Like most fungi, Fusarium are usually identified by macroscopic and microscopic features, although molecular methods such as 28S rRNA (ribosomal ribonucleic acid) gene-sequencing may also be used.

Pathogenicity and Clinical Significance

Fusarium exposure can adversely affect human health by three
mechanisms: infection (fusariosis), exposure to allergens, and exposure to toxics produced by
Fusarium. Fusarium frequently invade the skin, especially if the skin is damaged by trauma, burns, or diabetic
ulcers. Fusarium also can invade the eyes (endophtalmitis), nasal
sinuses, and lungs. Localized Fusarium infections may disseminate
through the bloodstream to become life-threatening infections.

Invasive disseminated Fusarium infections commonly occur in
immunocompromised persons, such as those with leukemia, lymphoma, or HIV
infection; those who are malnourished or neutropenic;
persons suffering from burns or other skin trauma; and persons taking
immunosuppressive drugs following bone or organ transplantation. Invasive
Fusarium infections can spread through blood vessels and cause
tissue infarction (tissue death).

The rate of Fusarium invasive infection is on the rise and now
makes up 1 to 3 percent of all invasive fungal infections. Disseminated
invasive Fusarium infections have high mortality rates that range
from about 30 to 90 percent.

F. solani is the most common cause of skin and disseminated invasive Fusarium infections (about 50 percent), followed by oxysporum (about 20 percent) and verticillioidis and monilforme (about 10 percent each).

Fusarium also produce a variety of toxins (mycotoxins), including fumonisins, trichothecenes, and zearalenones. Domestic animals and humans have become acutely ill after eating foods contaminated with Fusarium mycotoxins.

Fumonisins can increase the risk of some cancers, can damage the immune system, and can cause respiratory problems. Trichothecenes damage the immune and nervous systems, block cell protein synthesis, and cause vomiting. Zearalenones are estrogen-mimicking chemicals that can cause early female puberty, infertility, and spontaneous abortion in humans and other mammals. Human studies have linked consumption of Fusarium-contaminated corn (maize) with higher rates of early female puberty. Exposure to airborne Fusarium spores can also worsen asthma and sinus problems.

Drug Susceptibility

Fusarium infections are sometimes difficult to diagnose in their
early and less serious stages. Infections can often be diagnosed by culturing
Fusarium from the blood and from skin lesions. High resolution
computed
tomography (CT) scans of the chest are often useful in
diagnosing fusariosis. Polymerase chain reaction (PCR) blood tests also are used
to diagnose Fusarium infections.

Localized Fusarium
skin
infections can often be treated with topic antifungal drugs
such as natamycin and voriconazole. Disseminated Fusarium
infections are often difficult to treat because few antifungals are consistently
effective against many Fusarium species. Amphotericin B is often
used as a first-line drug against Fusarium; however, roughly 50
percent of Fusarium isolates, including many
solani and verticilloides, are resistant to
amphotericin B. Some Fusarium strains are susceptible to
voriconazole and posaconazole, while few Fusarium isolates are
susceptible to itraconazole. Most Fusarium strains are resistant
to the new echinocandin drugs (anidulafungin, caspofungin, and micafungin). These
chinocandin drugs are generally effective in treating disseminated
Aspergillus and Candida infections.

Other treatments that may be helpful in some cases of fusariosis include surgical debulking of Fusarium-infected tissue, removal of contaminated catheters, and using granulocyte-colony-stimulating factors.

The best method for controlling Fusarium infections is
avoidance of the mold. Medical experts recommended that immunocompromised persons
who are hospitalized be placed in rooms with positive air pressure, air
filtration, sterile water, and adequately cleaned surfaces, sinks, and showers to
reduce the risk of Fusarium infection. Any water damage or
visible mold growth in hospital rooms should be cleaned immediately. To
significantly reduce exposure to Fusariumand their mycotoxins in
the home, persons should keep dry, clean, and refrigerated all stored food, such
as grains, fruits, vegetables, and animal feeds.

Bibliography

Marom, Edith M., et al. “Imaging of Pulmonary Fusariosis in Patients with Hematologic Malignancies.” American Journal of Roentgenology 190 (2008): 1605-1609.

Nucci, Marcio, and Elias Anaissie. “Fusarium Infections in Immunocompromised Patients.” Clinical Microbiology Reviews 20 (2007): 695-704.

Patridge-Hinckley, Kimberly, et al. “Infection Control Measures to Prevent Invasive Mould Diseases in Hematopoietic Stem Cell Transplant Recipients.” Mycopathologica 168 (2009): 329-337.

Samson, Robert, Ellen Hoesktra, and Jens Frisvad. Introduction to Food and Airborne Fungi. 7th ed. Utrecht, the Netherlands: Central Bureau for Fungal Cultures, 2004.

Stanzani, Marta, et al. “Update on the Treatment of Disseminated Fusariosis: Focus on Voriconazole.” Therapeutics and Clinical Risk Management 3 (2007): 1165-1173.

Webster, John, and Weber, Roland. Introduction to Fungi. New York: Cambridge University Press, 2007.