General a. Etiologic Agent . The primary reservoir is rodents. Domestic cats and wild carnivores can also transmit plague to humans. In endemic or epidemic plague, the disease is transmitted via infected fleas from rodent to human, dog or cat to human, or person to person. Respiratory droplet transmission can occur person to person or cat to person.
Respiratory transmission is enhanced in humid climates.
Plague may also be transmitted via cat bites or scratches. The disease progresses with bacteremia, resulting in metastatic infection, septic shock, and thrombosis of small arteries, resulting in digital gangrene. Pneumonia due to hematogenous metastasis occurs in approximately 25 percent of cases. The case fatality rate for untreated bubonic plague is approximately 60 percent, but is less than 5 percent with prompt, effective therapy. Primary pneumonic plague occurs after inhalation of organisms, which may occur via aerosol transmission from a person or animal with secondary or primary pneumonic plague.