A fungus likely transmitted by scientists studying frogs. Greg Cochran writes in West Hunter:
… It took some time for herpetologists to admit that this chytrid fungus is the main culprit – some are still resisting. First, it was a lot like how doctors resisted Semmelweiss’ discoveries about the cause of puerperal fever – since doctors were the main method of transmission. How did this fungus get to the cloud forests of Costa Rica? On the boots of herpetologists, of course.
It’s also possible that psychiatrists spread mental disease germs.