We humans can drive species toward extinction by hunting them or destroying their habitat. But we can also threaten them in a more subtle but no less dangerous way: by making them sick.

In the early 1900s, humans introduced malaria-spreading mosquitoes to Hawaii, and many native bird species were decimated. More recently, a fungus introduced to the United States from Europe has proved lethal to several species of bats.

Now, scientists and wildlife managers are struggling to prevent the next infectious disaster. A recently discovered fungus is killing salamanders in Europe. It is likely spread by the pet trade and could soon arrive in North America, home to about half of all salamander species.

For months, biologists have been calling for a halt to the trade in pet salamanders so they can mount a defense against the fungus. But federal officials have yet to take action.