Rickettsial Infections

Rickettsia are some of the smallest bacteria, which are about as big as large viruses. They are obligate parasites that are grown in live media.

Transmission
Transmitted by an arthropod vector such as fleas, ticks, and mites.

Infection
1-2 week incubation period followed by fever, chills and a rash. May lead to circulatory system collapse, which can result in death. Some strains have a high mortality rate

Diagnosis
Antigen-antibody reactions (serology), which tests for antigens. Often too complicated to culture.

Treatment
Tetracycline (doxacycline) is useful for all Rickettsial infections

Louse-borne
Causes epidemic typhus, and has a 50% mortality rate. Common in the homeless and prisons. It is transmitted through lice.

Flea-borne
Causes endemic typhus, associated with water and ships. Carried by the fleas on rats. Causes a mild fever, no deaths.

Tick-borne (rocky mountain spotted fever)
Rash on wrists and ankles, and then begins to spread. 20% mortality rate untreated, and 5-10% mortality rate treated. It is more common in the spring and summer because ticks wake up and search for blood

Mite-borne
Scrub typhus, associated with chiggers that live on grass when larval, and mice when mature. Causes a 50% mortality rate, and is more common in Asia and Australia.

Q-fever
Caused by Coxiella burnetii from unpasturized milk. They can form endospores but few cause symptoms. They can be treated with tetracycline.

Cat scratch
Caused by Bartonella henselae, following a cat scratch or bite, and can go systemic in AIDS patients. DOC: Azithromycin