Naturally occurring cases of plague are seen in which country?

Naturally occurring cases of plague have been documented in the United States, particularly in the southwestern region. This is primarily due to the presence of suitable environments for the plague bacteria, Yersinia pestis, and the rodents that carry it, such as prairie dogs and ground squirrels. Given this context, the assertion that there are no naturally occurring cases of plague in the United States, Canada, or Mexico is not accurate.

The correct understanding highlights that the United States does report naturally occurring cases, especially in states like New Mexico, Arizona, and Colorado. Additionally, while Canada and Mexico do not report as many cases, there is still potential for the plague to exist in certain wildlife populations. Therefore, the assertion that the answer is 'None of the above' fails to acknowledge the notable occurrences within the United States.