Fungi produce innumerable “mycotoxins” – compounds that are toxic to humans. In mushrooms, these cause symptoms ranging from gastrointestinal upset to death (see FFF#091–100 for more). Although these are of significant concern to mushroom hunters, their impact is relatively small. The most significant mycotoxins in terms of the number of people affected are produced by molds that naturally grow on food. Over the next few weeks, I will discuss some of the most problematic food-borne mycotoxins. Topping that list are the aflatoxins, which cause liver cancer and are especially problematic for people in developing nations.
Tagged: fungal fiends
fungi working against humans and/or ecosystem balance
Coffee Rust, also known as Coffee Leaf Rust and in Spanish as “roya,” is a disease of coffee plants that is caused by the fungus Hemileia vastatrix.1–3 H. vastatrix is, as its common name implies, a member of the rusts (FFF#130). Unlike most rusts, however, it has a simple infect-sporulate life cycle, which is likely one reason the disease has been so successful.1 Coffee Rust is a particular problem in Central America, produces 15% of the world’s arabica coffee and exports roughly 432 million kilograms of coffee to the United States annually. The region suffered a devastating outbreak of the disease in the early 2010’s and has yet to fully recover.4–6
Fungi appear in the news with surprising frequency. However, many of those stories do not provide any new information. Below is a summary of what we’ve learned about fungi from March through April 2017. Read below to learn about: C. auris in the U.S., aflatoxin-destroying corn, viruses defying fungal incompatibility, fungus-farming ant evolution, bat and salamander diseases, and more! Visit the associated links to get the full story.
Sirex noctilio, known as the “Sirex woodwasp” or “European woodwasp” (sometimes spelled “wood wasp”), is an invasive species that attacks most species of pine trees. Interestingly, the insect is dependent upon the fungus Amylostereum aerolatum to complete its life cycle. The Sirex woodwasp carries the fungus with it to new trees and in return the fungus becomes a meal for the Sirex woodwasp’s larvae.
Fungi appear in the news with surprising frequency. However, many of those stories do not provide any new information. Below is a summary of what we’ve learned about fungi from November 2016 Through February 2017. Read below to learn about: two-fungi lichens, the fate of bananas, battery recycyling, Crohn’s disease, orcas, human pathogenic fungi, and more! Visit the associated links to get the full story.
Histoplasmosis is a fungal disease caused by the fungus Histoplasma capsulatum. Like the other true human fungal pathogens, H. capsulatum lives as a mold in the environment but switches to an infective yeast form in the body. In nature, H. capsulatum grows on bird or bat droppings. This fungus is very common, especially in the Ohio and Mississippi River valley areas. However, H. capsulatum very rarely causes disease. As with most fungal diseases, people with a weakened immune system are most at risk of acquiring histoplasmosis.
Coccidioidomycosis, otherwise known as “Valley fever,” is the most virulent human fungal pathogen. The disease is caused by the fungi Coccidioides immitis and C. posadasii, which normally live in arid soils. When they are disturbed by wind, construction, or human activity, spores from these fungi can become airborne and end up in peoples’ lungs. There, the spores germinate and can cause infection. Most of the time, the infection is mild and does not need to be treated. Occasionally, however, this progresses to more severe forms that sometimes require lifelong treatment. As with other human fungal diseases, Valley fever is more likely to cause severe disease in people with weakened immune systems.
In opportunistic fungal infections (FFF#161), fungi behave as they normally do, without drastically changing their cell structure or physiology. On the other hand, true fungal pathogens of animals can grow as both yeasts and hyphae. The fungus Candida albicans is somewhere in between these two groups. It normally inhabits healthy skin but can cause infection in people with a weakened immune system. In fact, it is one of the most virulent opportunistic pathogens. However, C. albicans can grow both as a yeast and as hyphae, making it morphologically more similar to true pathogenic fungi. C. albicans causes some of the most common fungal diseases, including: thrush, “yeast infections,” and invasive candidiasis.
This October, I will be discussing human fungal infections. Although fungi can be extremely problematic for certain species of animals and plants, fungi cause humans relatively few problems. There are roughly 300 species of fungi that cause disease in humans, but the most common ones cause nuisance infections of the skin. About 20-25% of the global population has a fungal skin infection like ringworm, athlete’s foot, and similar diseases. Although annoying, these infections are not very severe. There are a few fungi that cause more severe diseases, but these are much less common. The most dangerous type of fungal infections are the opportunistic infections. These are caused by normally benign fungi that take advantage of unusual conditions, such as when a patient has a weakened immune system.
Chytridiomycosis is a disease causing precipitous declines in frog and salamander populations on a global scale. There are two fungi responsible for this disease: Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandivorans (Bsal). The former can infect all amphibians while the latter infects only salamanders and newts. Both of these pathogens belong to the fungal phylum Chytridiomycota. Fungi in this phylum (“chytrids”) have a very simple cell structure and produce spores with flagella. Because of this, they can easily swim through water and infect amphibian hosts.