Rickettsia prowazekii (Louse-borne Typhus)
Rickettsia prowazekii is a small intracellular gram-negative Rickettsia that causes louse-borne Typhus. The great epidemics of typhus that plagued humans since ancient times ceased shortly after World War II with the widespread application of insect control procedures and other hygienic measures. Rickettsia prowazekii is transmitted from person to person by lice and fleas. The disease is transmitted particularly by the body louse Pediculus humanus corporis. Infection of humans occurs by contact of mucous membranes or abraded skin with the feces of the lice or fleas that have bitten a person with acute typhus fever. Infection probably also occurs by inhalation of dust contaminated with infected insect feces or body parts. Japan weaponized typhus during World War II. The Soviet Union, Canada, Germany, the United Kingdom and the United States investigated the use of Rickettsia prowazekii as a biological weapon.

Rickettsia rickettsii (Rocky Mountain Fever)
Rickettsia rickettsii is a species of gram-negative, aerobic Rickettsia that is the aetiologic agent of Rocky Mountain Spotted Fever. Its cells are slightly smaller and more uniform in size than those of Rickettsia prowazekii. Rocky Mountain spotted fever was first recognized in 1896 in the Snake River Valley of Idaho and was originally called "black measles" because of the characteristic rash. By the early 1900s, the recognized geographic distribution of this disease grew to encompass parts of the United States as far north as Washington and Montana and as far south as California, Arizona and New Mexico. Canada researched the viability of Rickettsia rickettsii as a biological weapon agent.

Coxiella burnetti (Q Fever)
Q fever is a zoonotic disease caused by Coxiella burnetii, a Rickettsia-like organism that is distributed globally. Coxiella burnetii is the only organism of its species. Humans are often very susceptible to the disease, and very few organisms may be required to cause infection. Ingestion of contaminated milk, followed by regurgitation and inspiration of the contaminated food, is a less common mode of transmission. Other modes of transmission to humans, including tick bites and human to human transmission, are rare. Coxiella burnetii is a highly infectious agent that is rather resistant to heat and drying. It can become airborne and inhaled by humans. A single C. burnetii organism may cause disease in a susceptible person. This agent could be developed for use in biological warfare and is considered a potential terrorist threat. The United States weaponized C. burnetti.