article_snippet.sent: The only infectious disease that humans have eradicated is smallpox.
article_snippet.sent: Like Polio, smallpox was a viral disease spread from person to person and would infect everyone in the absence of vaccination.
article_snippet.sent: And there's no non-human animal in nature that hosts these viruses, making it easier to eradicate than a disease that animals carry, too (although at least 100,000 monkeys were killed in the development of polio vaccines in the mid-20th century, according to the Smithsonian).
article_snippet.sent: A big difference, though, is that smallpox has obvious characteristic symptoms: fever and rash.