Emergomyces is a biphasic fungus capable of exhibiting both sterile megaspore and yeast-like morphologies under varying environmental conditions. The differing tissue phases can lead to distinct pathological manifestations: 1. Sterile megasporomycosis primarily presents as a chronic pulmonary disease, predominantly observed in rodents but infrequently in humans; 2. Emergomycosis is characterized by small, spherical yeast-like cells from the genus Emergomyces(Es.). Currently, seven species of Emergomyces have been identified: Es. pasteurianus, Es. africanus, Es. canadensis, Es. europaeus, Es. orientalis, Es. crescens, and Es. sola. With the exception of Es. sola, all known species can cause disseminated diseases in humans. Cases have been reported in Europe, North America, China, and Africa, albeit with a limited number of occurrences. Notably, Es. Crescens has been associated with pulmonary spirochetosis, although it is not classified as a disseminated disease. Emergomyces can lead to disseminated mycosis in immunocompromised individuals, such as those infected with HIV, solid organ transplant recipients, patients with hematological malignancies, or individuals on immunosuppressive therapy, often presenting with secondary skin lesions post-infection.
The emerging fungi exhibit typical characteristics of biphasic fungi, forming smooth, colorless colonies at 25°C and subsequently producing yellowish to white aerial mycelia after a period of growth. Microscopic examination reveals branched structures of the mycelium, with numerous conidia generated along the mycelial branches or on short-stemmed branches. The yeast cells of the genus, particularly Es. orientalis, typically range in size from 4 to 10 µm, resembling those of Bacill species. The lung lesions caused by Emergomyces may radiographically mimic those of pulmonary tuberculosis, occasionally leading to misdiagnosis.
Emergomyces predominantly exists as mycelium in soil. The exposure and pathogenic mechanisms involve the release of spores from the soil into the atmosphere. Upon inhalation, these spores can undergo temperature-dependent transformation within the lungs, forming yeast-like cells that proliferate via budding, leading to pulmonary disease in susceptible individuals. Yeast-like cells may disseminate through the bloodstream, aided by macrophages, resulting in extra-pulmonary infections [1–2]. Although human Emmonsia infections are rare in clinical practice, their associated mortality rate hovers around 50%. Currently, there are no sensitive or specific serological tests or biomarkers available for diagnosis, and the positive rates for sputum or bronchoalveolar lavage fluid specimens remain low. Thus, early diagnosis, prompt treatment, and immune enhancement are critical, with appropriate antifungal therapy being essential for patient outcomes.
In this case, both alveolar lavage fluid culture and fungal cultures returned negative results; however, NGS identified the presence of Aemonella orientalis with identification confidence of 69.47% (sequence number 2987) and Aemon orientalis with identification confidence of 0.2% (sequence number 1664), underscoring the significant improvement in clinical diagnostic capability afforded by NGS technology.
Current treatment guidelines for emerging mycosis, based on observational studies and expert consensus, recommend administering liposomal amphotericin B (L-AmB) (3–5 mg/kg/day) for 10–14 days in cases of disseminated disease in immunocompromised patients. Itraconazole maintenance therapy (200 mg orally, twice daily) should then be continued for 12 months, contingent upon immune reconstitution [2–4]. The patient in this case demonstrated a favorable clinical response to L-AmB therapy and was subsequently transitioned to oral voriconazole prior to discharge, with continued positive treatment outcomes noted during follow-up.
The diagnosis of emerging mycosis poses a significant challenge, even for seasoned clinicians and dermatologists. With advancements in medical therapies that suppress patients’ immune functions for various conditions, the incidence of fungal infections—including rare pathogens—has markedly increased. Thus, it is imperative that clinicians remain vigilant for these infections and utilize molecular technologies such as next-generation sequencing (NGS) to facilitate early diagnosis and identification of rare pathogens. There is an urgent need for the development of efficient and sensitive detection methods.
Notably, the administration instructions for liposomal amphotericin B (at a dosage of 10 mg) state that the initial dosage is 0.1 mg/kg/day, with subsequent increases to 0.25–0.5 mg/kg/day on the second day, ultimately reaching a maintenance dose of 1–3 mg/kg/day. However, pertinent literature recommends an initial dosage of 3–5 mg/kg/day for treating Emergomyces infections. Clinically, many practitioners often opt for conservative dosing due to the potential adverse reactions associated with amphotericin B, such as hypokalemia and leukopenia. This conservative approach may inadvertently prolong the overall treatment duration and escalate the financial burden on patients. Considering the disparity between dosing guidelines and literature recommendations, it is essential for experts in the field to provide more definitive dosing protocols in the future, ensuring the safe and effective use of antifungal agents in clinical practice.