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Overview of Rickettsial Infections


William A. Petri, Jr

, MD, PhD, University of Virginia School of Medicine

Reviewed/Revised Jan 2024
Topic Resources

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:

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 White blood cells .

Where damage occurs and how the body responds determine which symptoms develop.


Symptoms of Rickettsial Infections

Different rickettsial infections tend to cause similar symptoms:

  • Fever

  • Severe headache

  • A characteristic rash

  • A general feeling of illness (malaise)

A sore covered by a black scab (eschar) may form at the site of the bite. Because the rash often does not appear for several days, early rickettsial infection is often mistaken for a common viral infection, such as influenza. People may have swollen lymph nodes.

As the infection progresses, people typically experience confusion and severe weakness—often with cough, difficulty breathing, and sometimes vomiting.

When the infection is advanced, gangrene may develop, the liver or spleen may enlarge, the kidneys may malfunction, and blood pressure may fall dangerously low (causing shock Shock Shock is a life-threatening condition in which blood flow to the organs is low, decreasing delivery of oxygen and thus causing organ damage and sometimes death. Blood pressure is usually low... read more ). Death can result.

Diagnosis of Rickettsial Infections

  • A doctor's evaluation

  • Blood tests and biopsy of the rash

Because rickettsiae and rickettsia-like bacteria are transmitted by ticks, mites, fleas, and lice, doctors ask people

  • Whether they have been bitten by a tick or another vector

  • Whether they have traveled to an area where these infections are common

Being bitten is a helpful clue—particularly in geographic areas where rickettsial or a related infection is common. However, many people do not recall such a bite.

If doctors suspect Q fever, they may also ask whether people were at or near a farm (because cattle, sheep, and goats are the host for the bacteria that cause this infection).

Symptoms also help doctors diagnose these infections. Doctors ask people

  • How long it took for the rash to appear after they were bitten (if known)

  • Whether they have other symptoms

A physical examination is done to determine which parts of the body are affected and what the rash looks like. Doctors also look for an eschar (a sore covered by a black scab) that people may not have noticed and for swollen lymph nodes.


Testing is usually needed to confirm the diagnosis. Often, doctors cannot confirm an infection with rickettsiae or rickettsia-like bacteria quickly because these bacteria cannot be identified using commonly available laboratory tests. Special blood tests for these bacteria are not routinely available and take so long to process that people usually need to be treated before test results are available. Doctors base their decision to treat on the person's symptoms and the likelihood of possible exposure.

Useful tests include

  • Blood tests that detect antibodies to rickettsiae or rickettsia-like bacteria

  • If people have a rash, removal of a small sample of affected skin for testing (biopsy)

Doctors use two techniques to make the bacteria easier to detect and identify:

  • In immunofluorescence assays, foreign substances produced by the bacteria (antigens) are labeled with a fluorescent dye.

  • The polymerase chain reaction (PCR) technique is used to increase the amount of the bacteria's DNA, so that the bacteria can be detected more rapidly.

Treatment of Rickettsial Infections

  • Antibiotics

Antibiotics are usually started without waiting to get the results of tests. Early treatment of rickettsial infections can prevent complications from developing, reduce the risk of dying, and shorten the recovery time.

Rickettsial infections respond promptly to early treatment with antibiotics called tetracyclines (doxycycline is preferred). These antibiotics are given by mouth unless people are very sick. In such cases, antibiotics are given intravenously.

Although some tetracyclines taken for longer than 10 days can cause tooth staining in children younger than 8 years old, a short course (5 to 10 days) of doxycycline for rickettsial disease in children of all ages is recommended by the American Academy of Pediatrics and other experts and can be used without causing tooth staining or weakening of tooth enamel (see also Centers for Disease Control and Prevention (CDC): Research on doxycycline and tooth staining).

Ciprofloxacin Fluoroquinolones Fluoroquinolones are a class of broad-spectrum antibiotics that are used to treat a variety of infections. Fluoroquinolones include the following: Ciprofloxacin Delafloxacin Gemifloxacin read more and other similar antibiotics may be used to treat Mediterranean spotted fever but are usually not used to treat other rickettsial or related infections.

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