Related fungi are fairly benign and feed on decayed plants rather than live animals. Bd, by contrast, has hundreds of genes that produce proteins that can digest amphibian skin. Genetic studies have shown that samples of Bd from around the world are very similar and that the most dangerous variety has existed for less than century. So Bd is a single, recently evolved, highly anomalous, variety that has spread rapidly.
This suggests two questions:
- How has BD spread so fast?
- How did a meat-eating fungus evolve from plant-eating ancestors?
So how did it arise? This is less clear but the the farming of bullfrogs creates high population densities that favour highly virulent varieties. With international trade bringing different varieties together in conditions that promote virulence the appearance of a virulent hybrid variety is no surprise - and has been seen in salamanders raised for bait.
So trade has spread this deadly disease and probably contributed to its existence. That, given the continued growth in world trade, is bad news. But there may be worse to come. The same factors that created and spread Chytridiomycosis are found in all trade in animals and plants. They may yet create new, highly virulent, diseases of chickens, pigs or even wheat.