By Bailey Kelly
In 2013, researchers set out to identify and characterise the cause of the systemic infections found in HIV-infected people in South Africa. They discovered that the infections were caused by a novel fungal species, later named Emergomyces africanus (E. africanus). Its DNA was found in 30% of soil samples tested in the Western Cape and 10% of air samples collected in an urban location in Cape Town.
DNA sequencing showed that the fungus was closely related to Emergomyces pasteurianus but formed its own new clade. You can think of it like lions and tigers; they both share a common ancestor but are different enough to be separate species.
E. africanus is known for its thermal dimorphic characteristic, which allows it to switch morphology based on temperature. In the environment (soil and air), it exists as a spore-producing mould in its hyphal form. However, when a human inhales these spores, the temperature increase triggers them to morph into pathogenic yeast cells. These yeast cells replicate rapidly and disseminate throughout the host, turning an environmental spore into a severe opportunistic pathogen in immunocompromised patients.
The fungus causes systemic disease, known as emergomycosis, which has a high case fatality rate.
Scientists built a surveillance system, collected samples for culturing, and performed histological analyses to identify the pathogen’s behaviour and characteristics.
A broad-range fungal Polymerase Chain Reaction (PCR) assay was introduced, enabling molecular identification of all fungi found in the samples. The samples were also submitted for phenotypic and genotypic characterisation (DNA sequencing). Clinical and laboratory data were also collected on all the patients.
Of the thirteen patients confirmed to be infected with E. africanus, all showed symptoms of emergomycosis, which include very low CD4+ T-cell counts, widespread skin lesions, anaemia, fever, weight loss and tuberculosis (TB)-like chest X-ray results.
The majority of the thirteen patients improved with antifungal therapy and antiretroviral treatment. Unfortunately, one of these patients died before treatment could commence, and another two patients died during treatment. Altogether, an observed fatality rate of 23% was shown, underscoring the danger of delayed diagnosis and treatment.
Eighty-five percent of the patients had chest X-rays that mimicked those associated with tuberculosis. The skin lesions were also easily mistaken for those found in more common nonfungal diseases. This complicated the diagnosis and treatment of E. africanus. It is now known that tissue biopsy and molecular testing are vital for its accurate diagnosis.
References:
Kenyon, C., Bonorchis, K., Corcoran, C., Meintjes, G., Locketz, M., Lehloenya, R., Vismer, H. F., Naicker, P., Prozesky, H., van Wyk, M., Bamford, C., du Plooy, M., Imrie, G., Dlamini, S., Borman, A. M., Colebunders, R., Yansouni, C. P., Mendelson, M., & Govender, N. P. (2013). A Dimorphic Fungus Causing Disseminated Infection in South Africa. New England Journal of Medicine, 369(15), 1416–1424. https://doi.org/10.1056/NEJMOA1215460;WGROUP:STRING:MMS
Schwartz, I. S., Govender, N. P., Sigler, L., Jiang, Y., Maphanga, T. G., Toplis, B., Botha, A., Dukik, K., Claire Hoving, J., Muñoz, J. F., De Hoog, S., Cuomo, C. A., Colebunders, R., & Kenyon, C. (2019). Emergomyces: The global rise of new dimorphic fungal pathogens. PLOS Pathogens, 15(9), e1007977. https://doi.org/10.1371/JOURNAL.PPAT.1007977
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