Fungal Infections: An Unknown Pandemic

Although human memory is prone to forgetfulness, the planetary catastrophe caused by the coronavirus has reminded us that pandemics of infectious origin are not a nightmare of bygone days. A fact that has previously been confirmed by the terrible AIDS pandemic, or others less intense, such as the 2009 influenza epidemic and the outbreaks of Ebola, Zika and Dengue, the last two are carried by insects.

However, a hidden pandemic remains among us, little known, but with a huge spread and increasing mortality: caused by microscopic fungi.

From secondary actors to main characters

Historically, mushrooms, in addition to nutritional value, caused superficial diseases (pityriasis versicolor, athlete’s foot, etc.), which were cured with little or no treatment. In addition, they were considered as secondary opportunistic microorganisms that intervened after the initial pathology, mainly bacterial or viral. The number of infectious fungi identified was relatively small.

This panorama has changed radically since the late 20th century. Some fungi are the main agents causing potentially fatal infections with high clinical frequency. In turn, fungal species classified as harmless are very often responsible for serious outbreaks in hospitals, while the number of fungal strains resistant to the few antifungal drugs available is alarming.

In epidemiological terms, it is believed that more than 1.5 million people die each year from fungal infections. This figure is higher than that caused by tuberculosis or malaria, if not to go further.

List of the most dangerous

Given the magnitude of the problem, WHO has established a list of particularly dangerous fungi. This classification alerts us that, despite their threat, these pathogenic agents do not receive sufficient attention or resources, making it difficult to assess their global impact and to develop a more precise program of action.

The most significant are pathogenic species of yeast, filamentous and/or dimorphic fungi (developing differently depending on the growth temperature) belonging to the genera Candida, Aspergillus, cryptococcus, histoplasm, blastomycetes And coccidioids, among others. In particular, fungal microorganisms albicans It is listed as the fourth cause of systemic infections spread through the bloodstream.

Much more serious, however, was the appearance candida golden. The U.S. Centers for Disease and Infection Control (CDC) considers it an “imminent threat.” These yeasts show unusual resistance to treatment, which has increased the number of reported cases of multiresistance. In addition, it is insensitive to common sanitary disinfectants, can be transferred from hospital equipment and instruments (fomites), and is easily transmitted from person to person.

Vulnerable population is increasing

The reasons for this alarming situation are many and complex. On the one hand, over the past decades, the population susceptible to fungal infections, such as the elderly, newborns or patients with chronic debilitating diseases, has significantly increased in the world.

Closely related to these categories are people with damaged or directly suppressed immune systems, in the case of AIDS patients, those who have undergone invasive surgery or transplantation, and those who are undergoing long-term antibiotic or chemotherapy therapy. Similarly, long periods of hospitalization increase the risk of nosocomial infections (acquired in the hospital) caused by fungi.

British newspaper recently Guardian warned of this alarming situation. The article highlights serious shortcomings in proper infrastructure and sufficient research to deal with a possible outbreak of a fungal pandemic.

few medicines available

The lack of safe and effective antifungal therapy is the issue of greatest concern: since fungi are eukaryotic organisms, like us, the toxicity that compounds can involve is low.

In addition, we have a very limited arsenal of antifungal agents. In fact, there are only three families: polyenes (amphotericin B), azoles (ketoconazole or fluconazole), and echinocandins (caspofungin or micafungin). The first two target ergosterol, the main fungal plasma membrane compound; while echinocandins block the synthesis of its cell wall.

Some compounds are also used against certain localized mycoses (terbinafine, griseofulvin, ciclopirox…). However, its effectiveness is often weak, since it does not kill cells (fungicidal action), but only stops their growth (fungistatic).

In the meantime, strains resistant to conventional antifungal drugs are multiplying. Several molecules are at an advanced stage of research awaiting resolution in the future.

Another hurdle is the lack of vaccines against human fungal diseases. While there are currently some lawsuits going on, it is difficult to resolve this issue. First, because a significant number of potentially harmful fungi coexist with the healthy human microbiota. In addition, the clinical course of a fungal infection often depends on the patient and their immune response capacity.

Therefore, without falling into extreme panic, more attention should be paid to fungi. Not forgetting, of course, other, more worrying microbiological threats, such as those caused by antibiotic-resistant bacteria or the presence of genetically new viruses unknown to the human population.

Juan Carlos Argüelles Ordonez, professor of microbiology. Signaling and response to stress in pathogenic yeasts. Antifungal mechanisms of action: new natural products. University of Murcia

This article was originally published on The Conversation. Read the original.