Fungal species of the genus Fusarium are opportunistic pathogens and may cause fusariosis. Immunocompromised patients are particularly prone to Fusarium infection and in these individuals, hematogenous spread of pathogens may lead to disseminated, life-threatening disease.
Patients suffering from fusariosis usually have a medical history of immunosuppression and/or hospitalization, i.e., they belong to any of the aforementioned risk groups. Long-term use of corticosteroids as well as neutropenia or lymphopenia may indicate an immunosuppression in people not previously diagnosed with disorders of the immune system. In contrast, immunocompetent individuals may not report recently sustained minor traumas that may have facilitated Fusarium infection unless inquired about.
Most frequent initial manifestations of fusariosis are dermatitis, onychomycosis, and keratitis. In immunocompetent individuals, an exacerbation of symptoms is unlikely since pathogens don't typically spread from the primary site of entry. In immunocompromised patients, dermatitis may turn into ecthyma, cellulitis, panniculitis and soft-tissue necrosis. The appearance of multiple subcutaneous nodules indicates the hematogenous spread of pathogens. Furthermore, patients may develop sinusitis and pneumonia. Less commonly, fusariosis may trigger septic arthritis  and osteomyelitis . Dissemination is common in those patients who suffer from Fusarium-induced thrombophlebitis or peritonitis. Infiltration of neighboring tissues as well as systemic spread are generally associated with constitutive symptoms like malaise and fever.
Although fusariosis is generally considered a rare disease, Fusarium spp. are among the most common fungal pathogens isolated from immunodeficient patients. Thus, characteristic skin lesions or keratitis in immunocompromised individuals should prompt a strong suspicion of Fusarium infection. Histopathological examination of tissue samples is strongly recommended to confirm this suspicion, although in vivo confocal microscopy and anterior segment optical coherence tomography may be utilized to diagnose ocular fungal infections . Fusarium spp. grow in form of hyaline, septate hyphae that measure up to 8 μm in diameter and largely resemble Aspergillus filaments. Hyphae branch at right or acute angles. Canoe- or banana-shaped macroconidia may be observed and are characteristic of the genus; the precise appearance of microconidia is of importance to distinguish species . If histopathological analyses don't allow for a reliable diagnosis, fungi have to be cultured. Of note, Fusarium spp. spread hematogenously, and blood cultures do yield positive results in about half of patients. Nevertheless, negative results don't rule out fusariosis or fungal infections triggered by pathogens of other genera. For a long time, isolation of Fusarium spp. from infected sites has been the diagnostic measure of choice, but more recently, the identification of fungal pathogens by means of molecular biological techniques has been gaining importance . Antimicrobial susceptibility testing is recommended to assure an optimum response to therapy and to avoid further dissemination of the disease.
Although diagnostic imaging is not required to confirm Fusarium infection, plain radiography or computed tomography scans of the thoracic cavity often reveal poorly demarcated, angioinvasive masses in the lungs of patients presenting with respiratory infection. The latter technique is more sensitive than the former, but both lack specificity to diagnose fusariosis .
Antimycotic treatment is the mainstay of fusariosis therapy, but isolates may vary largely with regards to their susceptibility to determined compounds . Clinical trials have not yet been conducted and according to empiric evidence, amphotericin B deoxycholate, lipid-based amphotericin B formulations, voriconazole and posaconazole are most indicated to this end. Amphotericin B deoxycholate is more likely to provoke side effects than lipid-based formulations; posaconazole should be reserved for patients suffering from severe fusariosis and those infected with multi-resistant strains . Furthermore, ketoconazole and nystatin as well as combined regimens have occasionally been applied with success. In contrast, fluconazole and itraconazole have repeatedly been proven ineffective. Fusarium spp. commonly show multiple resistance and thus, the selection of an effective antimycotic drug should be based on the results of susceptibility testing. An early initiation of treatment is of particular importance in immunocompromised individuals and may avoid systemic spread. Here, systemic administration of the aforementioned antifungal drugs should be complemented with surgical debridement of infected tissues. Whenever possible, the underlying immunosuppression should be remedied.
Evidence regarding the efficacy of an adjuvant therapy with granulocyte colony-stimulating factor or granulocyte–macrophage colony-stimulating factor is scarce. At this moment, such an approach can thus not be recommended.
Immunocompetent patients diagnosed with localized fusariosis generally respond well to antimycotic therapy and have an excellent prognosis. In contrast, disseminated fusariosis is often refractory to antimicrobial therapy and Fusarium infection of immunocompromised individuals is related to mortality rates of 50 to 80%. Intractable immunosuppression accompanied by persistent neutropenia, graft-versus-host disease and continued immunosuppressive therapy are unfavorable prognostic factors to this end  . Moreover, these conditions are associated with a high risk of recurrence in survivors.
Fusariosis may be caused by a wide variety of fungi of the genus Fusarium. The respective species are widely distributed in soil, air and plants, and may be encountered in virtually all geographic regions, including deserts and polar regions . Accordingly, large parts of the population are exposed to Fusarium spp. and indeed, these fungi have been proven to colonize mucous membranes of healthy individuals. More than a dozen species have been related to fusariosis, with the following species being isolated most commonly :
Species occasionally causing Fusarium infection are :
Fusarium spp. differ in their propensity for cutaneous, ocular and respiratory infection. Morover, minimal inhibitory concentrations of distinct antimycotics against Fusarium isolates may vary considerably . These facts emphasize the need for a reliable identification of the causative agent.
Immunosuppression is the most important risk factor for Fusarium infection and subsequent systemic spread. In this context, patients suffering from hematological malignancies or neutropenia, and those in need of solid organ or stem cell transplants and adjuvant immunosuppressive therapy constitute major risk groups. Use of catheters and peritoneal dialysis may be associated with Fusarium-induced thrombophlebitis, fungemia and peritonitis. On the other hand, skin-penetrating trauma and burns as well as use of contact lenses predispose immunocompetent individuals for fusariosis.
Although Fusarium infection is generally considered a rare disease, Fusarium spp. are second only to Aspergillus spp. as causative agents of life-threatening fungal infections in immunodeficient patients. As has been indicated above, Fusarium infection is a major complication of hematological malignancies and neutropenia. In this context, incidence rates of up to 4.5 per 1,000 patient-years have been observed . According to a retrospective study on fusariosis after hematopoietic stem cell transplantation, this fungal infection is to be expected in 0.5 and 2% of patients who receive transplants from matched, related and unmatched donors, respectively . Epidemiological data regarding racial and gender predilection as well as the patients' age at symptom onset are largely influenced by the underlying disease. Patient cohorts considered in the aforementioned studies consisted of approximately equal parts of men and women, and their reported age at diagnosis ranged from 2 to 77 years.
Fungal pathogens are present in distinct environments and rigorous measures have to be undertaken to reduce a patient's exposure to Fusarium spp. Accordingly, the vast majority of the population is constantly exposed to these opportunistic agents. In healthy individuals, an infection is prevented by the mechanical barrier posed by the skin, by antimicrobial compounds in tears and the integrity of the cornea, and by immune cells that act upon inhalation of Fusarium spp. or in case fungi overcome the aforementioned barriers. The latter happens rather frequently, e.g., in case of cutaneous lesions, micro-lesions of the cornea provoked by the use of contact lenses, or skin-penetrating medical procedures. Thus, immune cells like neutrophil granulocytes play the key role in avoiding Fusarium infection. In healthy individuals, an inoculation of pathogens does usually not even result in a localized infection with clinical symptoms. In contrast, neutropenic patients are most susceptible to fusariosis.
No specific measures can be recommended to prevent Fusarium infection in immunocompetent individuals. However, adequate measures should be undertaken to minimize the exposure of immunodeficient patients to fungal pathogens, and to avoid systemic dissemination of etiological agents in case of a suspected infection:
Due to wide-spread resistances among Fusarium spp., prophylactic administration of antimycotics is not generally recommended.
Fusarium infection or fusariosis refers to an infection with fungal species of the genus Fusarium. Fusarium spp. are opportunistic pathogens and while there are case reports regarding fusariosis triggered by many distinct species, F. solani, F. oxysporum and F. verticillioides are most commonly isolated from men . Immunosuppression is the single most important risk factor for Fusarium infection and also increases the individual risk of hematogenous spread and systemic disease. However, immunocompetent patients may present with fusariosis if an infection is facilitated by the breakdown of mechanical and functional barriers or the presence of foreign bodies. Usually, affected people suffer from dermatitis or cellulitis, onychomycosis, keratitis, and respiratory infection, possibly accompanied by constitutive symptoms like malaise and fever.
Treatment should comprise antimycotic medication and therapy of the underlying immunosuppression. With regards to the former, both polyene and azole antimycotics have been used. Unfortunately, most patients presenting with fusariosis suffer from non-curable primary diseases like hematological malignancies, or require prolonged immunosuppressive therapy to prevent organ transplant rejection. These conditions are unfavorable prognostic factors and therefore, mortality rates in immunocompromised patients by far exceed 50% .
Of note, Fusarium spp. may release mycotoxins, mainly trichothecenes and fumonisins. Ingestion of contaminated products may thus lead to different forms of food poisoning. For instance, mycotoxin T2 exposure has been associated with Kashin-Beck disease. The discussion of Fusarium-related mycotoxicosis is beyond the scope of this article, though.
Fusarium infection or fusariosis refers to an infection with fungal species of the genus Fusarium. These fungi may release mycotoxins and are more commonly known for poisoning of livestock and men, since otherwise healthy individuals rarely contract an infection with live pathogens. Occasionally, dermatitis, onychomycosis, and keratitis may be triggered by Fusarium species. In this context, skin-penetrating traumas and use of contact lenses are important predisposing factors. Such fungal infections are curable and patients have an excellent prognosis.
In contrast, fusariosis is a life-threatening disease in immunodeficient individuals. Patients suffering from hematological malignancies, neutropenia, and those in need of solid organ or stem cell transplants and adjuvant immunosuppressive therapy are at rather high risks of Fusarium infection. Initially, the disease manifests as described for immunocompetent patients, but fungi tend to spread via blood vessels throughout the whole body. Systemic fusariosis is typically accompanied by malaise and fever, and the majority of affected individuals respond poorly to antifungal medication. Disseminated Fusarium infection is associated with mortality rates of more than 50% and thus, every possible effort should be undertaken to avoid an infection in the first place. At home, preventive measures consist in avoiding cutaneous as well as corneal lesions whenever possible. Medical attention should be sought to receive proper wound care when necessary. In hospitals, severely immunodeficient patients are generally placed in special rooms equipped with air filters.