In the 2023 American post-apocalyptic drama television series The Last of Us, humans are thrust into extinction due to a fungal brain infection that turns most species into zombies.
It may sound far-fetched, but fungi can and do infect the human brain. Fungi are present throughout our environment: in the air, in the soil, in decaying plant material, on our skin and even in our intestines as part of our natural flora.
Microscopic pathogenic fungi can invade various parts of the body, causing a range of symptoms and health issues. In fact, fungal infections contribute to approximately 1.5 million deaths every year.
A team recently published a review of the emergence and re-emergence of fungal infections in Africa, particularly in sub-Saharan Africa. The continent is suffering from a silent epidemicbut the face, yeast infections.
The increase in fatal fungal infections in the region is mainly due to a high burden of HIV infections, lack of access to quality health care and unavailability of effective antifungal drugs.
What are fungal infections?
For most of human history, fungal infections have never been a threat to human health. This is mainly because most fungi cannot survive the hot human body temperature of 37°C. However, climate change and other environmental pressures have led to the emergence of fungal species able to survive human body temperature.
Even so, our immune system is able to fight off fungal infections. For example, our bodies can create localized acidic environments, limit the availability of micronutrients, and release antimicrobial agents.
However, when the immune system is weakened, fungi are able to evade the body’s defenses and avoid detection. They can generate bioactive agents that help them escape or adapt to the host’s immune response. Some adapt to survive in harsh environments with few nutrients and oxygen.
Immunocompromised people are at risk of developing serious or life-threatening fungal diseases. Africa is responsible for 67% of the global HIV burden and opportunistic fungal diseases are on the rise.
An example of opportunistic fungal diseases is cryptococcal meningitiswhich emerged with the HIV pandemic in the late 1980s. Today, sub-Saharan Africa accounts for approximately 73% of all cases and deaths from the disease worldwide.
Cryptococcal meningitis is caused by the fungus Cryptococcus neoformans, found in soil and bird droppings. Yeast infection occurs when someone inhales fungal spores. This leads first to the development of a lung infection and later to a fatal brain infection. Cryptococcal meningitis is one of the leading causes of adult meningitis in sub-Saharan Africa and is associated with nearly 20% of all deaths AIDS related.
Effective treatments for cryptococcal meningitis are out of reach for most affected people. Costs range from $1,400 to $2,500 per patient for a full two-week antifungal course.
The development of cheaper drugs has been hampered by a limited understanding of how the fungus causes such extreme brain damage.
Another example of HIV-related opportunistic fungal disease is Pneumocystis jirovecii pneumonia. It is caused by a ubiquitous aerial fungus, Pneumocystis jirovecii, which is passed from person to person.
Pneumocystis cause little problem in people with a healthy immune system, but they act as reservoirs and transmit the infection to immunocompromised people, who can develop severe symptoms, including fever, dry cough and difficulty in breathing. Pneumocystis jirovecii pneumonia occurs in 15-20% of HIV-infected patients who have breathing problems.
The diagnosis of Pneumocystis jiroveci pneumonia is expensive and requires a well-equipped laboratory. In poor urban and rural health facilities in Africa, this will be a challenge. The fungus, P. jirovecii, is also extremely difficult to cultivate, limiting diagnosis and research.
The review revealed several factors behind the emergence and re-emergence of fungal threats. They include the climate changethe spread of immunosuppressive diseases, medical advances such as organ transplants (the immune system is suppressed to minimize rejection), the use of immunosuppressants to control inflammatory diseases, and the use of antibiotics.
Although these factors are not unique to Africa, the burden of fungal diseases and the number of people who die from them are much greater.
The covid pandemic appears to have aggravated the global fungal burden. For example, recent studies have shown that people who have been infected with covid and have recovered are vulnerable to infection with a fungus called mucormycosis, also known as black fungus.
Covid-induced lung damage, hyperglycaemia and the steroids often used to treat them are predisposing factors to black mycosis. With a reduced ability to clear fungal spores and a reduced immune response to steroids, the fungus can enter and infect the face, eventually moving to the brain.
But don’t we have antifungal drugs?
Most of the population affected by fungal infections live in poorer rural or urban areas.
With underfunded and overstretched healthcare systems, many African countries are not well prepared to deal with yeast infections. Additionally, some of the antifungal drugs recommended by the WHO – such as flucytosine – are not available in most African countries. Sometimes ineffective and even quite toxic remedies are used instead.
the emergence of drug resistant fungal strains it is also a growing threat. The increase in multi-drug resistant Candida species, azole resistant Aspergillus species and clinically resistant Cryptococci is of great concern.