Recent Spike in Plague Cases in Western US

The White-Throated Wood Rat, is a proven carrier of plague vector fleas.

The White-Throated Wood Rat, is a proven carrier of plague vector fleas.

Medical Research: What is the background for this study? What are the main findings?

Response: Plague, a bacterial disease that is endemic to the Western United States, is most famous for the destruction it caused during the Middle Ages when it killed over half the population of Europe.  Today, plague still infects people around the world and there are a handful of cases each year here in the U.S.  However, this year where there are normally 3-7 cases, there have been 12 cases since the beginning of April.

Medical Research: What should clinicians and patients take away from your report?

Response: One of the main reasons CDC issued our report on this year’s plague cases was because we want to remind clinicians and their patients that plague should be considered as a diagnosis if the symptoms, travel history, and exposure fit.  Most cases occur between late spring and early fall, so there might still be more cases this year.  It’s good to be aware of three things: where cases occur, how the disease is spread, and how to prevent it.

  1. Most cases occur in the Western United States, and so far this year the cases have been from Arizona (two), California (one), Colorado (four), Georgia (one, but exposed in California), New Mexico (two), Oregon (one), and Utah (one).
  2. Plague is spread when fleas become infected by feeding on rodents, such as chipmunks, prairie dogs, ground squirrels, mice, and other mammals that are infected with the plague bacterium Yersinia pestis. Fleas then spread the plague bacteria to humans and other mammals during their next feeding.
  3. Most important, CDC recommends that people who live in or travel to the Western United States wear long pants when possible and use insect repellent on clothing and skin when outside. People also should avoid direct contact with ill or dead animals and never feed squirrels, chipmunks, or otherwild rodents. In addition, pet owners should regularly use flea control products on their pets and consult a veterinarian if their pet is ill. Rodent habitat can be reduced around the home by removing brush, clutter, and potential rodent food sources such as garbage or pet food. If you have any symptoms of plague, please see a clinician and let them know where you’ve traveled and if you’ve had contact with rodents.

Medical Research: What recommendations do you have for future research as a result of this study?

Response: We know that the number of plague cases can vary from year to year, which more cases in some years than others.  This is likely due to the complex ecology of plague spread among rodents that are reservoirs for the disease.  Exploring this more may help us be better able to advise people who live in and visit the Western United States about their risk for plague.


Human Plague — United States, 2015

MMWR Weekly August 28, 2015 / 64(33);918-91 

Natalie Kwit, DVM1,2; Christina Nelson, MD2; Kiersten Kugeler, PhD2; Jeannine Petersen, PhD2; Lydia Plante, MSPH3; Hayley Yaglom, MPH3; Vicki Kramer, PhD4; Benjamin Schwartz, MD5; Jennifer House, DVM6; Leah Colton, PhD6; Amanda Feldpausch, MPH7; Cherie Drenzek, DVM7; Joan Baumbach, MD8; Mark DiMenna, PhD9; Emily Fisher, MD1,10; Emilio Debess, DVM10; Danielle Buttke, DVM11; Matthew Weinburke, MPH11; Christopher Percy, MD12; Martin Schriefer, PhD2; Ken Gage, PhD2; Paul Mead, MD is not a forum for the exchange of personal medical information, advice or the promotion of self-destructive behavior (e.g., eating disorders, suicide). While you may freely discuss your troubles, you should not look to the Website for information or advice on such topics. Instead, we recommend that you talk in person with a trusted medical professional.

The information on is provided for educational purposes only, and is in no way intended to diagnose, cure, or treat any medical or other condition. Always seek the advice of your physician or other qualified health and ask your doctor any questions you may have regarding a medical condition. In addition to all other limitations and disclaimers in this agreement, service provider and its third party providers disclaim any liability or loss in connection with the content provided on this website. Interview with:, & Natalie Kwit DVM (2015). Recent Spike in Plague Cases in Western US