The world continues to discuss the challenges to addressing antimicrobial resistance. You have probably heard of MERS (methicillin-resistant Staphylococcus aureus), VRE (vancomycin-resistant enterococci), and MDR-TB (multi-drug resistant tuberculosis). What these commonly discussed pathogens have in common is that they are all bacteria or viruses. What you don’t commonly hear about are antimicrobial resistant fungal infections. But they exist, and may have the potential to be worse for humanity than the resistant bacteria or viruses.
Humans and fungi
For a little background on how animals, bacteria, viruses, and fungi are related, check out the figure below. You can see that bacteria are pretty far away from us (animals) on the tree of life. They are their own complete branch of the tree, and viruses, while not on this chart, can be found down where bacteria and archaea/eukaryota branches split. Now check out the eukaryota branch. You can see we (animals) are really quite close to fungi. We are literally right next to each other on the tree of life. What this means is that we (animals) are much more closely related biologically to fungi than we are to bacteria or viruses. This is a very important fact when it comes to anti-fungal medications.
Because bacteria and viruses are so drastically different biologically than humans, the ways the antimicrobial agents work to kill them tend not to cause serious damage to us. We are just too different biologically to suffer the same fate as the bacteria or viruses inside of us that we are trying to kill. The same cannot be said of fungi. Because we are so similar to fungi on a biological level, it is incredibly difficult to develop drugs that kill the fungi but don’t seriously harm us. So when those fungi become resistant to the drugs we do have, that can spell disaster.
The fungus among us
So who are getting fungal infections and which ones are becoming resistant to anti-fungal medications?
Anyone can get a fungal infection. Fungi are found all around us. We come into contact with fungi everyday and most of us don’t get sick. Common fungal infections happen on the skin, nails or vaginal yeast infections. You may have had some of these fungal infections before, or know someone who has. People with weakened immune systems are the most likely to get a serious or deadly fungal infection. Some fungal diseases include aspergillosis, blastomycosis, candidiasis, valley fever, histoplasmosis and ringworm. For those of us with proper immune systems many fungal infections are annoying but not deadly. However, with anti-fungal resistance, that may be changing.
Because serious fungal infections occur most often in people with weakened immune systems, they are a big issue in hospital settings. The fungus Candida is the most common cause of healthcare-associated bloodstream infections in the US. And some Candida species are becoming resistant to first and second-line medications. Additionally, there are reports of a new species, Candida auris, which is a newly emerging fungus that includes strains resistant to all classes of anti-fungals. As with all antimicrobial resistance, the remaining treatment options that exist for resistant infections are expensive and can be toxic for patients who are already sick. Anti-fungal resistance is predicted to continue to increase unless we do something to stop it.
What can we do
In short, we have to develop new anti-fungal medications and people taking any anti-fungal medication have to take them properly. But anti-fungal drug development is challenging.
Some of the currently used anti-fungal medications were developed over 50 years ago. The newest class of anti-fungals was discovered in the 1970s and took 30 years to make it into clinical practice. The science of developing anti-fungal agents is unpredictable and challenging. Many current research projects are testing anti-fungal candidates that interfere with fungal cell wall development. But as with all drug development, it’s hard to know what will and won’t make it to clinical production. To successfully address the need for new anti-fungal medication pharmaceutical industries need to partner with academic laboratories. This partnership would combine the strengths of both institutions and hopefully accelerate anti-fungal drug development.
All is not lost, yet. While fungal infections present challenges that bacterial or viral infections do not, the same principles apply when attempting to prevent anti-fungal resistance. A coordinated and early effort to address anti-fungal resistance is our best chance at preventing future deaths due to resistant fungal infections.