Plague (Yersinia pestis)

OVERVIEW
Yersinia pestis—gram-negative, bipolar staining rod; an Enterobacteriaceae; reservoir includes wild rodents (sylvatic), ground squirrels, prairie dogs, rabbits, bobcats, coyotes
Occurs worldwide
U.S.—reported cases from New Mexico, Arizona, California, Colorado, Idaho, Nevada, Oregon, Texas, Utah, Washington, Wyoming, and Hawaii
Common from May to October
Infected vectors (fleas) transmit the bacterium in bite.
Bacteria—rapidly migrate from skin lymphatics to regional lymph nodes; survive phagocytosis (because of capsule protection) and multiply in lymph nodes; phagocytic cells rupture and organism is resistant to further phagocytosis.
Infection—fever and painful lymphadenopathy (bubo); intense local inflammation results in bubonic plague; intermittent bacteremia; lymph nodes may rupture; may become septicemic with or without lymph node involvement
Cats—highly susceptible to infection; severe fatal disease
Dogs—naturally resistant to infection