Rickettsiae are obligate intracellular parasites of humans; they are most often transmitted by the bite of infected ticks, lice, and fleas. Other rickettsiae that are transmitted via lice include Bartonella (Rochalimaea) quintana, the agent of trench fever. Trench fever was a significant medical problem during World War I and has recently reappeared among AIDS victims and homeless and alcoholic persons.

Coxiella Burnetti

Coxiella burnetti was part of the US stockpile prior to its destruction in 1972.

Disease	Q fever, Query fever, Balkan influenza, Balkan grippe, pneumorickettsiosis, abattoir fever
Natural Hosts	Sheep, goats, cattle; wild animals, with numerous tick hosts
Incubation Period	2 weeks to 1 month
Symptoms	Fever, severe frontal headache with retro-orbital pain, profuse sweating, myalgia, and nausea. Pulmonary involvement in half the cases. Asymptomatic in many cases. Chronic form with endocarditis
Treatment	Antibiotics, including tetracycline
Fatality Rate if Untreated	2.4 percent for the acute form; 60 percent if chronic endocarditis develops

Coxiella burnetti are typically spread in nature by the Brown Dog Tick, Rhipicephalus sanguineus; the Rocky Mountain Wood Tick, Dermacentor andersoni; and the Lone Star Tick, Amblyomma americanum. Unlike most other Rickettsiae, C. burnetti is very resistant to environmental degradation.

Rickettsia typhi

Disease	Murine typhus, flea-borne typhus fever, endemic typhus fever, urban typhus
Natural Hosts	Rats and mice; transmitted by flea or lice
Incubation Period	1-2 weeks
Symptoms	Gradual onset of fever with severe headache, chills, generalized pains and dry cough (sometimes developing to bronchopneumonia) of about 2 weeks. A macular rash appears by about 5 days, first appearing on the trunk and lasting about six days. CNS manifestations are possible. Damage is caused to vascular endothelia by invasion of rickettsiae, possibly leading to thrombosis and hemorrhage.
Treatment	Doxycycline, tetracycline, and chloramphenicol
Fatality Rate if Untreated	1-2 percent

Endemic typhus, which is caused by Rickettsia typhi, is a different disease from typhoid fever, which is caused by Salmonella typhi and by eating or drinking food or water contaminated with bacteria.

Rickettsia prowazekii

Disease	Epidemic typhus
Natural Hosts	Humans, also squirrels; transmitted by lice
Incubation Period	6-15days
Symptoms	Fever, aches, headaches, weakness, and pain; stupor and delerium
Treatment	Doxycycline, tetracycline, and chloramphenicol
Fatality Rate if Untreated	30 percent

Epidemic typhus, which is caused by Rickettsia prowazekii, is a different disease from typhoid fever, which is caused by Salmonella typhi and by eating or drinking food or water contaminated with bacteria.

Rickettsia rickettsii

Disease	Rocky Mountain spotted fever
Natural Hosts	Mammals, including dogs, rodents, and other small animals; transmitted by ticks that feed on infected animals
Incubation Period	3 to 14 days
Symptoms	Sudden onset of fever (that can last for 2 or 3 weeks), severe headache, fatigue, red, swollen eyes, muscle pain, and chills. In 2 to 6 days, a maculo-papular rash typically starts on the wrists and ankles but quickly spreads to the rest of the body and may become hemorrhagic
Treatment	Doxycycline, tetracycline, and chloramphenicol
Fatality Rate if Untreated	20-25 percent

The ticks that generally transmit Rocky Mountain spotted fever are large ticks (American Dog Tick, Dermacentor variabilis; Rocky Mountain Wood Tick, D. andersoni), in contrast to the small ticks (Deer Tick, Ixodes scapularis; Pacific Black-Legged Tick, I. pacificus) that generally transmit the spiral-shaped bacterium that causes Lyme disease. However, the larger Lone Star Tick, Amblyomma americanum is capable of transmitting both diseases.

Photograph © Department of Pathology
University of Kansas School of Medicine.