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Antiviral drugs may be a new treatment strategy in the fight against Candida auris

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Antiviral drugs can make antifungals work again.

That, at its simplest, is the approach Mohamed Seleem’s lab at the Center for One Health Research has found may be a key treatment strategy in the battle against Candida auris, a frighteningly deadly fungal pathogen discovered in 2009 that is considered an urgent threat by the Centers for Disease Control and Prevention (CDC).

Candida auris, first discovered in Japan as an ear infection, has a staggering 60 percent mortality rate among those it infects, primarily people with compromised health in hospitals and nursing homes.

Recently, Seleem and Ph.D. students Yehia Elgammal and Ehab A. Salama published a paper in the American Society for Microbiology’s Antimicrobial Agents and Chemotherapy journal detailing the potential use of atazanavir, an HIV protease inhibitor drug, as a new avenue to improving the effectiveness of existing antifungals for those with a Candida auris infection.

A perfect storm of antimicrobial resistance, global warming and the COVID-19 pandemic has resulted in the rapid spread of Candida auris around the world, said Seleem, director of the center, a collaboration between the Virginia-Maryland College of Veterinary Medicine and the Edward Via College of Osteopathic Medicine.

We don’t have lots of drugs to use to treat fungal pathogens. We have only three classes of antifungal drugs. With a fungal pathogen, it’s often resistant to one class, but then we have two other options. What’s scary about Candida auris is it shows resistance to all three classes of the antifungal.

The CDC has a list of urgent threats, but on that list there is just one fungal pathogen, which is Candida auris. Because it’s urgent, we need to deal with it.”

Mohamed Seleem, the Tyler J. and Frances F. Young Chair in Bacteriology at Virginia Tech

Widespread use of fungicides in agriculture, in addition to the three classes of antifungal drugs used widely in medicine, has contributed to fungal pathogens developing more resistance, particularly Candida auris.

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Also, its rise has been linked to rising global temperatures and to easier spread through hospitals filled with COVID-19 patients in recent years during the global pandemic.

Atazanavir, an HIV protease inhibitor drug, has been found by Seleem’s lab to block the ability of Candida auris to excrete antifungals through its efflux pumps.

Think of a boat taking on water and hoses siphoning that water out of the boat to keep it afloat. Atazanavir stops up the hoses.

That allows the azole class of antifungal drugs to not be expelled as easily and perform better against Candida auris, the Seleem lab’s research has found.

The research on atazanavir builds on work three years ago by Seleem’s lab, then at Purdue University, finding potentially similar benefit in lopinavir, another HIV protease inhibitor.

HIV protease drugs are already in wide use among HIV patients, who can also be extra susceptible to Candida auris. Some HIV patients have likely been taking HIV protease drugs and azole-class antifungals in tandem for separate purposes, providing a potential source of already existing data that can be reviewed on whether those patients had Candida auris and what effects the emerging pathogen had on them.

Repurposing drugs already on the market for new uses can allow those treatments to reach widespread clinical use much more rapidly than would happen with the discovery of an entirely new drug, as existing drugs have already been tested and approved by the Food and Drug Administration and have years of further observation of effects in prescriptive use.

In 2022, the Center for One Health Research received a $1.9 million grant from the National Institutes of Health for the Seleem lab’s research on repurposing already approved drugs for treating gonorrhea.

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Source:

Possible pathways of C. auris emergence and the hypothetical role of interspecies transmission

In a recent study published in the journal Clinical Microbiology and Infection, researchers in Spain, summarized the current understanding of the emergence and ecologic niches of Candida auris.

Study: Climate change, animals, and Candida auris: insights into the ecological niche of a new species from a one health approach. Image Credit: Kateryna Kon/Shutterstock.com
Study: Climate change, animals, and Candida auris: insights into the ecological niche of a new species from a one health approach. Image Credit: Kateryna Kon/Shutterstock.com

Background

C. auris was first identified in a Japanese inpatient in 2009. The United States (US) Centers for Disease Control and Prevention (CDC) categorized the pathogen as an urgent threat. Moreover, C. auris has been designated as a fungal pathogenic species of critical concern by the World Health Organization (WHO) in their fungal priority list in October 2022.

Five clonally distinct clades of this fungus emerged independently and concurrently on three continents. Whole-genome sequencing of 47 isolates identified many single nucleotide polymorphisms (SNPs) with minimal intra-regional genetic diversity, suggesting a near-contemporary emergence in distinct geographic locations.

In the present study, the authors discussed the likely pathways of the emergence of C. auris and the role of inter-species transmission. In doing so, the study postulates that climate change has played a major role in high thermotolerant C. auris emergence. Thus, hypothesizing that climate change induced an environmental ancestor to become pathogenic through thermal adaptation.

Hypothetical emergence due to global warming

Global warming is proposed as the likely explanation for the independent and contemporary emergence of distinct C. auris clades. Few fungal species are pathogenic in endothermal animals and humans; very few fungi thrive at mammals’ high basal temperatures, creating a thermal barrier preventing infections.

Several reports suggest that increasing environmental temperatures due to climate change may result in the selection of thermotolerant fungal lineages that can circumvent the thermal barrier and infect/colonize endothermic animals.

One study showed that C. auris could grow at elevated temperatures than its close phylogenetic relatives. In addition, the remarkable halotolerance exhibited by this fungus suggested that it could have previously existed as an environmental species in wetlands/marshes.

These ancestors might have become pathogens in humans after gaining thermotolerance due to climate change adaptation. Nevertheless, this hypothesis cannot explain the geographic dispersion of the independently evolved clades of C. auris.

Ecological niche(s) of C. auris

The first environmental isolates of C. auris were reported in 2021 from a salt marsh in the Andaman Islands and recently in Colombian estuaries. Notably, one of the isolates was less multidrug-resistant and less heat-tolerant.

It was also significantly different from clinical isolates suggesting a higher similarity to its wild ancestors from marine ecosystems.

C. auris also exhibits high-stress resistance, allowing for continued survival in stressful environments. This plasticity might contribute to its emergence and growing prevalence. Further, this fungus was detected in stored but not freshly pickled apples in India, suggesting a new human transmission pathway and a possible selection route for drug-resistant isolates in agriculture, storage, and supply chains.

Isolation from animal cultures or the environment has not been documented yet. Nonetheless, a study employing in silico DNA metabarcoding screened the internal transcribed spacer region in public datasets.

DNA metabarcoding identified partial matches in non-human sources, such as activated sludge, air dust, the ear canal of a dog with otitis, peanut fields, and the skin of newts. This provided evidence of the ubiquitous presence of the fungus in anthropogenic and natural environments.

One Health approach to understand and manage C. auris

One Health is an integrative, collaborative, multi/trans-disciplinary approach for sustainable balance and optimization of the health of humans, animals, and ecosystems.

Zoophilic fungi and, hypothetically, C. auris might have a dual life cycle wherein host, and environmental reservoirs may serve as durable sources of propagules. This might contribute to the global rise of emergent fungal diseases across continents.

Concluding remarks

The striking plasticity and the ability of C. auris to adapt to harsh environments could allow the fungus to thrive in sludge, wastewater, and fresh/marine waters.

Global warming, the impact of changes in the environment and human population, and indiscriminate antifungal use in agriculture might have led to C. auris evolving into a much more resistant/invasive pathogen that can infect/colonize endothermic animals.

Aquatic marine hosts could have spread primitive strains to humans. Therefore, adopting the One Health approach can help understand the relationship between animal/human health and ecological changes as factors in the emergence and transmission of fungal pathogens.

Journal reference: