We’ve written before about fungal infections devastating amphibian, honey bee, and bat populations, but this winter we wanted to delve more deeply into this issue. First, we’ll learn a bit about fungi and why they can be such virulent pathogens. In the next few posts, we’ll explore the emergence of these infections in bats, honey bees, frogs, and yes, even in humans.
What is a fungus?
A fungus is not an animal or a plant. It isn’t a bacteria either. Fungi belong to a separate kingdom that includes molds, yeasts, lichens, and mushrooms. Animals and fungi do share certain features: they breathe oxygen and get energy by eating food. Their cells are similar. Yet fungi don’t eat and digest their food as animals do. Their feeding style breaks down dead plants and animals, decomposing them. But they can also switch their diet from dead animals to live cells.
Fungi can retreat into spores and survive for long periods without food. They can live independently, outside their hosts. As spores they can float through the air, get lodged into the treads of a shoe, or float in water. Unlike bacteria and viruses that may burn themselves out when they kill their victims, fungi can wipe out whole populations without being destroyed themselves.
Why are certain types of animals so vulnerable to fungal diseases?
There isn’t one conclusive answer. Those animals that are immunosuppressed, however, tend to be more vulnerable to fungal infection. But why are these animals so unhealthy? The answers are complex and may have to do with many different causes, perhaps a “perfect storm” of causes: the overall decrease of biodiversity, use of pesticides, climate change, clear cutting of forests and habitat destruction and degradation, and other issues.
Readers of Frogs Are Green are familiar with the the chytrid fungus, Batrachochytrium dendrobatidis, which has wiped out hundreds of species of amphibians.
In 2006 the white-nose syndrome, an infection caused by the fungus Geomyces destructans killed a few bats in New York; since then it has killed more than 5 million bats in 21 states and four Canadian provinces.
Recently honey bee populations have been devastated. There is evidence that co-infection with multiple pathogens, including fungi, is one cause.
A fungus called Cryptococcus neoformans ravages humans with compromised immune systems. It is spread primarily by the guano of pigeons and contracted by inhaling spores. More than 1 million immunosuppressed patients are infected annually around the world.
What is the Causing the Spread of the Emerging Fungal Diseases?
Fungal spores can be easily spread by humans so fungi that were once isolated in different parts of the world can now exchange genes and create new and more virulent pathogens.
As reported in a recent e360 (Yale) article: “Fungi have driven more animal species extinct than any other class of pathogens by quite a long way,” according to Matthew Fisher, an epidemiologist at Imperial College in London.
As Rob Miles, executive director of the Organization for Bat Conservation told Bee, Bat, Frog Deaths May Be Linked, Discovery News”>Discovery News, “It appears that many species are under an immense amount of stress, allowing opportunistic diseases to take hold.”
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