And to generalize it more, pests and diseases are rarely truly eradicated, that’s part of why smallpox is so notable, the virus only exists in laboratory settings anymore (and that’s partly because it’s a predominantly human disease). Usually eradication means in an area or in people in an area. Because of that it’s usually an active effort to keep it out. Measles was eliminated in the developed world, but it was still around, it was just kept at bay by mass vaccination. As vaccination rates fell it was able to come back through interactions with places it hadn’t been eliminated.