In which region of the United States are cases of Yersinia pestis most frequently located?

• A. New Mexico, Arizona, and California
• B. Alaska, Oregon, and Utah
• C. North and South Carolina and Virginia
• D. Ohio, Michigan, and Indiana

Answer: (A)

Yersinia pestis, the bacterium that causes plague, is primarily associated with areas in the western United States where it is most commonly found in wildlife populations, particularly among rodent species. The highest incidence of plague cases is reported in states such as New Mexico, Arizona, and California, which have the right ecological conditions and susceptibility in rodent populations. These regions offer a climate that supports the fleas that transmit the bacterium, allowing for outbreaks to occur.

In contrast, regions such as Alaska, Oregon, Utah, North and South Carolina, Virginia, Ohio, Michigan, and Indiana do not have the same level of endemic plague activity, as these areas do not have the appropriate ecological niches or wildlife reservoirs for Yersinia pestis. Thus, the significant clustering of cases in the southwestern states highlights their higher risk and provides essential information for public health monitoring and preventive measures in those regions.