The importance of Medical Mycology – Ελληνική Εταιρεία Ιατρικής Μυκητολογίας

The importance of Medical Mycology has increased significantly in recent years due to the steady increase in the number and severity of fungal infections, and the wide variety of emerging fungi, due to the changing environmental conditions. Basic research using modern genetics, molecular biology, immunology, biochemistry, and other research techniques has been applied to pathogenic fungi in humans and animals, contributing to a finer identification and classification of fungi. Considerable progress has been also made in the chemotherapy of both life-threatening deep mycoses and chronic superficial mycoses.

Fungi are the most abundant form of life on the planet, with approximately 12 million species present worldwide. Most of them have never been classified. Only a fraction of these species infects humans, but they are responsible for approximately one billion cases each year.

Fungal infections kill more than 1.5 million people each year, and the number is rising. Moreover, they affect the lives of over a billion people. However, they remain a neglected topic by public health authorities, even though most deaths from fungal infections are preventable. Serious fungal infections occur as a consequence of other health conditions, including asthma, AIDS, cancer, organ transplants, and treatments with corticosteroids and other immunomodulating drugs.

Early and accurate diagnosis allows immediate antifungal treatment. However, this is often delayed or unavailable, leading to death, severe chronic disease, or blindness.

The number of reported fungal infections increased by 400% during the years 1998-2015, possibly due to climate change. Other fungal infections appear to have increased as a result of the COVID-19 pandemic, including aspergillosis and mucormycosis. As these infections are more common in people with immunosuppression or lung damage, it is suspected that the fungi take advantage of the tissue damage caused by SARS-CoV-2.

Recent global estimates, roughly calculate that more than 3,000,000 cases of chronic pulmonary aspergillosis, ~223,100 cases of cryptococcal meningitis as HIV/AIDS sequelae, ~700,000 cases of invasive candidiasis, ~500,000 cases of Pneumocystis jirovecii pneumonia, ~250,000 cases of invasive aspergillosis, ~100,000 cases disseminated histoplasmosis, over 10,000,000 cases of fungal asthma and ~1,000,000 cases of fungal keratitis, occur annually.

Although the epidemiology of fungal infections has changed significantly in recent years, species like Aspergillus, Candida, Cryptococcus, Pneumocystis jirovecii, endemic dimorphic fungi such as Histoplasma capsulatum, and mucormycetes such as Rhizopus, remain the main pathogens responsible for most of the cases of severe fungal disease. Candida albicans is the main agent responsible for mucositis, Aspergillus fumigatus for most allergic mycoses, and Trichophyton species, especially T. rubrum, for dermatomycoses.

Fungi are also becoming increasingly resistant to the small number of available treatments, with very few alternatives in the pipeline.

The world was relatively unprepared for a virus pandemic when COVID-19 hit, but at least the scientific community developed vaccines against the coronavirus very quickly. However, no human vaccines have been developed yet against fungi.

In October 2022 the World Health Organization published the priority list of fungal pathogens, in the first global effort to create a mycological list of the 19 most dangerous fungi to humans. "Despite posing a growing threat to human health, fungal infections receive very little attention and resources globally” the report said."This all makes it impossible to estimate the exact burden of fungal infections, and consequently difficult to galvanise policy and programmatic action."

As serious as these fungal infections are, luckily most of them are not transmitted from person to person. Instead, they are usually transmitted environmentally, which tends to limit their local spread, avoiding the cause of pandemics. Mucormycosis, for example, is 70 to 80 times more prevalent in India than in the rest of the world. There are, however, exceptions to this rule. Candida auris, which "visited"us "out of nowhere" and probably appeared due to climate change, was unknown to scientists until its isolation from the ear canal of a 70-year-old woman in Tokyo in 2009. Within a few years, infections have been reported across Asia, Africa, and the Middle East. It has now spread all over the world and has become a real nightmare in hospitals, due to its resistance to many first-line antifungal drugs. It is also partially resistant to disinfectants and heat, which makes it extremely difficult to eradicate. Its detection can cause the temporary closure of entire hospital wards.

Having so many species of fungi in the environment, emerging fungal threats causing outbreaks is a scary scenario, and the number of scientists with expertise in Mycology able to monitor them, is small. Proper and targeted education of more of us in this interesting field would be a good start. Let us also not forget that fungi and yeasts may also present treatment opportunities, for example, the world's first antibiotic, penicillin, was discovered in a fungus. It is possible that many more chemical secrets or “tricks” are hiding in their mycelia! This is also an interesting field that needs to be explored.

Like bacteria or viruses, fungi are ancient organisms and can be found everywhere! It would be a mistake to underestimate them.

GEORGIOS PETRIKKOS MD, PhD

Professor Emeritus of Pathology - Infectious Diseases

References:

1. https://pubmed.ncbi.nlm.nih.gov/35352028/