Overview of rickettsial infections

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Rickettsial infections and related infections (such as anaplasmosis, ehrlichiosis, and Q fever) are caused by an unusual type of bacteria that can live only inside the cells of another organism.

Most of these infections are spread through ticks, mites, fleas, or lice.
A fever, a severe headache, and usually a rash develop, and people feel generally ill.
Symptoms suggest the diagnosis, and to confirm it, doctors do special tests that use a sample from the rash or blood.
Antibiotics are given as soon as doctors suspect one of these infections.

Rickettsiae and related (rickettsia-like) bacteria (such as Ehrlichia, Anaplasma, and Coxiella burnetii bacteria) are an unusual type of bacteria that cause several similar diseases, including the following:

Rocky Mountain spotted fever
Epidemic typhus
Ehrlichiosis
Anaplasmosis
Q fever

These bacteria differ from most other bacteria in that they can live and multiply only inside the cells of another organism (host) and cannot survive on their own in the environment.
Many species of these bacteria live in small animals (such as rats and mice), which are called the host. Cattle, sheep, or goats are the hosts for Coxiella burnetii, which causes Q fever. Humans are the usual host for Rickettsia prowazekii, which causes epidemic typhus. Host animals may or may not be ill from the infection.
Rickettsiae and rickettsia-like bacteria are usually spread to people through the bites of ticks, mites, fleas, or lice that previously fed on an infected animal. Ticks, mites, fleas, and lice are called vectors because they spread (transmit) organisms that cause disease from one host to another. Q fever, caused by Coxiella burnetii, can be spread through the air or in contaminated food and water and do not require a vector.
Each species of rickettsiae and rickettsia-like bacteria has its own hosts and usually vectors.
Some of these bacteria (and the diseases they cause) occur worldwide. Others occur only in certain geographic regions.
Some of these bacteria infect the cells lining small blood vessels, causing the blood vessels to become inflamed or blocked or to bleed into the surrounding tissue. Other bacteria (Ehrlichia and Anaplasma) enter white blood cells.
Where damage occurs and how the body responds determine which symptoms develop.