Milner Centre for Evolution

Researchers and students blog about their activities in this unique cross-faculty research centre bridging biology, health and education.

Why we care about emerging the fungal disease Candida auris

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Candida auris is a fungal disease that is emerging around the world and in the UK. It was only discovered and described in 2009, but since then it has been found in at least 15 countries, including 20 NHS trusts and 35 hospitals in the UK. While many new diseases generate both dismissive ‘not another one’ attitudes and ‘the end is nigh’ hysteria, fungal diseases rarely cause much of a ripple in public health compared to viruses or bacteria. However, there are several major reasons C. aruis represents a significant concern for those trying to keep the UK population healthy.

The early indications are that many of the infections it causes are life threatening, and it has characteristics that raise serious concern over the short and long term efficacy of antifungal drugs. Of the over 200 cases in the UK since 2016, more than 10% have been systemic bloodstream infections, typically the most serious kind of fungal infection. These systemic infections known as candidemia or fungemia are notoriously difficult to diagnose and treat. The persistent, localised and high mortality cases that have made up the bulk of the reported infections across the world are probably hospital acquired. Being acquired in the hospital puts the most vulnerable patients right in the way of C. auris. Patients with weakened immune systems and those requiring treatment for other diseases are the ones most likely to get C. auris infections. Even more troubling, some strains of C. auris appear to have natural resistance to all three classes of antifungal drugs. There are limited antifungal options in the clinic, and a hospital transmissible multidrug-resistant strain is quite threatening. If C. auris is able to persist in hospitals, then drug resistant strains may repeatedly emerge, and hospitals might become breeding grounds for the worst strains.

Compared to many other fungi, the emergence of this pathogen is occurring at a surprising pace. The earliest identifiable case of C. auris was found to be from 1996 a case originally thought to be a yeast. However, the recent outbreaks mostly from 2013-2017 across the world appear to stem from few origins with local strains being highly similar, suggests C. auris is either a rapidly spreading novel pathogen or is being newly pushed to emerge via new clinical conditions. Although there is good evidence for rapid spread of fungal diseases of animals and plants, there is virtually no precedence for a rapidly spreading fungal disease of humans. Most fungal diseases of humans are environmentally acquired and their spread tracks events in the environment rather than the clinic. Although, the sudden emergence of fungal diseases associated with the global AIDS epidemic appeared very rapid, the fungi themselves were already present. It remains to be determined what the driving factor is behind the rapid emergence of C. auris, but health agencies across the world are on the alert for new outbreaks and research is very active.

Finally, because it is a very recently discovered fungal disease, we know very little about its abilities and vulnerabilities. Studies so far have found that C. auris may display traits associated with virulence similar to other fungi such as biofilm formation and the production of protein degrading enzymes, but because scientists are only just beginning work with this fungus there are a lot of unknowns. It is not yet clear which if any specific traits enable C. auris to invade hosts or if strains differ in virulence. Similarly, although the evidence supports C. auris being resistant to antifungals, the mechanisms of resistance remain unknown. In the bigger picture, key questions remain. Where is C. auris from? Are the clinical strains different from strains outside the clinic? What is the route of transmission, if any, within and between hospitals? These unknowns make C. auris challenging for professionals and disconcerting for the public.

Last week was the first Fungal Disease Awareness Week set aside by the CDC, it is a good time to think about fungal diseases as a whole. C. auris is certainly not the only fungal disease or the one with the biggest impact on people in the UK or globally, but it is a piece of the picture. Because of its recent emergence, drug resistance, and within hospital transmission, C. auris is putting the community on alert and prompting more people to Think Fungus.

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