There is a large loophole in the law Invasive Alien Species Act: it does not encompass alien microorganisms. Under the present version of the law, only alien species that can be visually identified must be inspected, and species too small to see (such as viruses, bacteria, and fungi) are beyond the scope of the law. Even though Japan has laws designed to control infectious diseases and parasites that affect humans, domestic animals and plants, these laws do not cover wildlife. Infectious diseases that affect wildlife populations are emerging at unusually high rates, and currently pose a great threat to the global conservation of biodiversity. Given that more than 500 million live animals are imported annually into Japan, the microorganisms that accompany these animals are a cause for concern. Under such a situation, we have currently faced invasion of a serious worldwide disease of amphibians which is being caused by the chytrid fungus Batrachochytrium dendrobatidis. Results of our investigation suggested that the origin (natural host) of the fungus might be the Japanese amphibians, and that the fungus has expanded its distribution through worldwide amphibian trade. This case showed us the significance of biodiversity conservation from the viewpoint of epidemiology.