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.
This emerging fungal disease of ash trees was first reported in 1992 in Poland. Over the past 24 years, Hymenoscyphus fraxineus has spread throughout Europe and (with the help of the invasive Emerald Ash Borer beetle) is now poised to eradicate ash trees from the entire continent.
Snakes of the Eastern United States are dying of a disease called Snake Fungal Disease (SFD). Recently, the cause of SFD was identified as the fungus Ophidiomyces ophiodiicola. This fungus normally contributes to the decomposition of dead animals, but has for some reason been infecting live snakes since the early 2000’ SFD is primarily characterized by a severe rash on the snake’s skin, although it may also affect the snake’s eyes or even liver. The infection often results in death and in some species the mortality rate appears to be 100%.
Witches might not be real, but witches’ brooms certainly are – and they’re destroying chocolate! Yes, Halloween’s favorite treat (chocolate) is suffering at the hands of a disease with a Halloween-themed name: Witches’ Broom Disease. Witches’ brooms are actually fairly common and occur on many different plants. In chocolate trees (Cacao trees, Theobroma cacao, whose genus name literally means “food of the gods”), witches’ brooms are caused by the fungal pathogen Moniliophthora perniciosa and have an enormous economic impact on chocolate production in Central and South America.
The banana that you know and love may soon be a thing of the past. I know, you probably think that I’m exaggerating the threat to this ubiquitous crop, but the possibility of bananas disappearing from grocery shelves forever is very real. In fact, it nearly happened once before. Here is a brief history of the modern banana: in the 1950’s, bananas were wiped out by a disease called Panama Disease. To save the crop, a resistant variety was discovered. Today, Panama Disease has evolved to attack the resistant variety, thus threatening to decimate banana production for a second time. This time, however, there is not a fallback option.
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