Septicemic plague is a severe infection caused by the gram-negative bacillus Yersinia pestis, which is found in rodents (eg, prairie dogs, squirrels, rats) and their fleas and sometimes in cats. This bacterium can present as 3 distinct forms of illness: bubonic, pneumonic, and septicemic (bubonic and pneumonic are discussed separately).
The septicemic form of this disease occurs when the bacteria multiply in the blood, causing bacteremia and severe sepsis. Primary septicemic plague results from direct inoculation of the bacteria into the bloodstream, typically via the bite of an infected animal or flea or direct contact with infected tissues. Secondary septicemic plague occurs when there is progression of disease and dissemination of bacteria following bubonic presentation. Septicemic plague, either primary or secondary, has approximately 40% mortality when treated, and in untreated cases, the mortality is 100%.
Septicemic plague has sudden onset and rapid progression (with an incubation period of 1-6 days) causing fever, chills, weakness, abdominal pain, shock, and bleeding underneath the skin or other organs and may result in disseminated intravascular coagulation, necrosis of small vessels, and purpura. Acral regions such as the fingers, toes, and nose may become gangrenous, hence the term “black death,” the moniker for the second plague pandemic. Septicemic plague is rarely transmissible human to human but may become transmissible if the disease reaches the pneumonic stage.
Plague is endemic to the southwestern United States (Colorado, New Mexico, Arizona, California) as well as Vietnam, India, the former Soviet Union, and parts of Africa. Hikers, campers, veterinarians, and owners of infected cats, especially those living or visiting endemic areas, are at greater risk for contracting plague.
Other risk factors include rural or non-urban environment, especially in known endemic areas; contact with sick or dead animals, especially small rodents or other possible hosts; wilderness activities; known flea bite; occupation as veterinarian; and recent plague in the community.
Plague is classified as a Category A bioterrorism agent because of its ease of dissemination, contagiousness, and high mortality rate; however, the most likely method of dispersal would be as an aerosol, resulting in the primary pneumonic form.