Mucormycosis and Pythiosis – New Insights

Dr Ariya Chindamporn
Associate Professor
Department of Microbiology
Faculty of Medicine
Chulalongkorn University
Bangkok, Thailand

The revised taxonomy classifies fungi causing mucormycosis in the new subphylum Mucoromycotina.¹ This subphylum and the subphylum entomophthoromycotina were formerly among the 2 orders that were members of the zygomycota division.¹ The 2 subphyla are pathogens similar in size and both have aseptate hyphae; however, they differ in their infected host, clinical manifestation and spore types.¹ Rhizopus species is the most common mucormycosis-causing agent.²

Studies performed in mucormycosis patients worldwide revealed that the underlying conditions differ between patients in developed countries and those in developing countries. The European continent sees higher cases of underlying hematological malignancies in mucormycosis patients³ in contrast with countries such as India⁴ and Mexico,⁵ which report diabetes as the predominant underlying condition in their patients.

Pathogenesis of mucormycosis: Role of CotH receptor agents

The regulatory protein CotH on the surface of the mucorales fungi specifically bind to the glucose receptor protein GRP78 on the surface of the host endothelial cells. This interaction facilitates fungal invasion of the cell, subsequently causing damage to the endothelial cells, promoting angioinvasion and dissemination.⁶ Investigations show that interruption of CotH in Rhizopus oryzae is able to disrupt the invasive potential of the pathogen, making CotH a promising therapeutic target.⁶

Pythiosis: A fungus-like organism

An increasing trend in cases of human pythiosis has been observed in the past 10 years, with Thailand reported to have the highest number of cases worldwide.⁷ Clinical manifestations of human pythiosis can be classified into 4 types: cutaneous/subcutaneous; ocular; vascular; and disseminated pythiosis. In vascular pythiosis, 4 classic clinical presentations that should be of concern are underlying thalassemia, no atherosclerotic risk, history of previous leg wound and presentation with acute or chronic limb ischemia.⁸ The ocular form, on the other hand, is commonly linked to a history of eye contact with water, such as through contact lens wear and swimming pool use. Rapid and definite diagnosis and treatment are crucial to patients’ survival and preservation of the eye globe.

References

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2. Roden MM, et al. Clin Infect Dis 2005;41:634-653.
3. Skiada A, et al. Clin Microbiol Infect 2011;17:1859-1867.
4. Chakrabarti A, et al. Med Mycol 2006;44:335-342.
5. Corzo-Leon DE, et al. Med Mycol 2017 [Epub ahead of print].
6. Gebremariam T, et al. J Clin Invest 2014;124:237-250.
7. Krajaejun T, et al. Clin Infect Dis 2006;43:569-576.
8. Reanpang T, et al. Int J Low Extrem Wounds 2015;14:245-250.