Final answer:
False. Some pathogens, like HIV, do cause disease in humans only, but it is not implausible to use a second test subject.
Step-by-step explanation:
False. Some pathogens, like HIV, do cause disease in humans only, but it is not implausible to use a second test subject. HIV can be studied and tested on primates such as chimpanzees, as they share a similar immune system to humans. While it is true that studying human diseases directly in humans presents ethical concerns, researchers can still use alternative methods to understand and study diseases.