Fusarium
Fusarium is a group of widely distributed fungi known primarily as plant pathogens, but they also pose significant health risks to humans. These molds thrive on various substrates, including soil, decaying organic matter, and indoor environments, and can produce a range of allergens and mycotoxins. Fusarium can cause infections in humans, particularly in those with compromised immune systems, leading to conditions such as fusariosis, which can affect the skin, eyes, sinuses, and lungs. The severity of these infections can escalate, with mortality rates for disseminated cases reaching up to 90 percent.
Fusarium species, such as F. solani, are prominent culprits behind these infections, and they produce several harmful toxins that can lead to serious health issues, including respiratory problems and increased cancer risks. Diagnosis often involves culturing the fungus from infected sites and utilizing imaging techniques like CT scans. Treatment can be complicated due to the fungi's resistance to many antifungal medications. Preventive measures focus on maintaining cleanliness in environments, especially for immunocompromised individuals, to minimize exposure to Fusarium and its spores.
Fusarium
- TRANSMISSION ROUTE: Direct contact, inhalation
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 teleomorphic 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 three types of asexual spores, including macroconidia, chlamydospores, and microconidia. Macroconidia is 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 toxins 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 (endophthalmitis), 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 mycotoxins 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 Fusariumskin 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 and terbinafine. Many Fusarium strains are resistant to the echinocandin drugs (anidulafungin, caspofungin, and micafungin) because they have high minimum inhibitory concentrations. It is also difficult to determine which strains of Fusarium will be resistant to drugs. However, 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 Fusarium and their mycotoxins in the home, persons should keep dry, clean, and refrigerated all stored food, such as grains, fruits, vegetables, and animal feeds.
Bibliography
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