Human Plague on the Rise in the U.S.

September 4, 2015 in Aerowood Animal Hospital

Since April 1, 2015, a total of 11 cases of human plague have been reported in residents of six states: Arizona (two), California (one), Colorado (four), Georgia (one), New Mexico (two), and Oregon (one). Three patients aged 16, 52, and 79 years died.


Plague is a rare, life-threatening, flea-borne disease caused by the bacterium Yersinia pestis. It is unclear why the number of cases in 2015 is higher than usual. Plague circulates among wild rodents and their fleas in rural and semirural areas, usually in the western United States. Many types of animals, such as rock squirrels, wood rats, ground squirrels, prairie dogs, chipmunks, mice, voles, and rabbits can be affected by plague. Wild carnivores can become infected by eating other infected animals.


Transmission to humans occurs through the bite of infected fleas, direct contact with infected body fluids or tissues, or inhalation of respiratory droplets from ill persons or animals, including ill domesticated cats and dogs. In humans, plague is characterized by the sudden onset of fever and depression, which can be accompanied by abdominal pain, nausea, and vomiting.  The mortality rate for untreated plague has ranged from 66% to 93%; however, with medical treatment, the mortality rate drops to approximately 16%. Prompt treatment with antimicrobials greatly improves outcome.


Cats are particularly susceptible to plague and can contract it by eating infected rodents. Sick cats pose a risk of transmitting infectious plague droplets to their owners or to veterinarians. Dogs are less likely to be ill, but they can still bring plague-infested fleas into the home.


Persons engaging in outdoor activities in areas where plague is endemic should wear long pants when possible and use insect repellent on clothing and skin. Persons also should avoid direct contact with ill or dead animals and never feed squirrels, chipmunks, or other 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.

2015 Human Plauge

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