Rickettsial infections and rickettsia-like 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 the bites of infected 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 skin or blood.
The antibiotic doxycycline is given as soon as doctors suspect a person has one of these infections.
Rickettsial infections cause a variety of human and animal diseases worldwide. Rickettsiae bacteria can be transmitted (spread) between people and animals and cause infections (see Infections Caused by Rickettsiae). Infections that can be transmitted between people and animals are called zoonotic diseases, or zoonoses (see Introduction to Diseases Spread Between Animals and People (Zoonoses)). Sometimes, an insect is involved in transmitting an infection. Insects that carry and transmit bacteria between animals and people are called vectors, and the infections they spread are called vector-borne zoonoses.
Rickettsiae are an unusual type of bacteria that cause several similar infections:
Rickettsia-like bacteria cause the following infections:
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. Livestock, such as cattle, sheep, and goats, or, less commonly, other animals such as cats, are the hosts for Coxiella burnetii, which causes Q fever and can be spread from animals to people. Humans are the usual host for Rickettsia prowazekii, which causes epidemic typhus. Host animals and people 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 (vectors) that previously fed on an infected animal. . Not all rickettsia-like infections are spread by a vector. For example, Q fever is spread through the air or dust or in contaminated animal products such as raw milk.
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.
Some Rickettsial and Related Infections
Infection | Infecting Bacteria and Vectors (ticks, mites, or other insects that transmit infection) | Hosts | Areas Where Infection Occurs | Symptoms |
|---|---|---|---|---|
Typhus | ||||
Brill-Zinsser disease (a recurrence of epidemic typhus, sometimes years after the first infection) | Rickettsia prowazekii Transmitted by body lice or by unknown methods when the hosts are wild flying squirrels | People and wild flying squirrels | Throughout the world | About 8 to 16 days after the bacteria enter the body, symptoms begin suddenly, with high fever, intense headache, and extreme fatigue. A rash appears 4 to 6 days later. A rash does not always occur in Brill-Zinsser disease. |
Rickettsia typhi or Rickettsia felis Transmitted by fleas | Cats, rats, mice, other rodents, dogs, and wild opossums | Throughout the world | About 7 to 14 days after the bacteria enter the body, symptoms begin shaking chills, fever, and a headache. A rash may appear a few days after the other symptoms. | |
Scrub typhus | ||||
Orientia tsutsugamushi Transmitted by mite larvae (chiggers) | Mites (mites are both the vectors and the hosts) | South Asia, East Asia, Southeast Asia, the Arabian Peninsula, Chile, and Kenya, rare in the United States | About 7 to 10 days after the bacteria enter the body, symptoms begin suddenly, with fever, chills, severe headache, and swollen lymph nodes. A black scab (eschar) may develop at the site of the chigger bite. A rash appears about 5 to 8 days after the fever starts. | |
Spotted fevers | ||||
Rickettsia rickettsii Transmitted by ticks | Rodents | Most of the United States; and Central and South America | About 3 to 12 days after the bacteria enter the body, symptoms begin suddenly with a severe headache, chills, extreme exhaustion, and muscle pains. | |
Rickettsia africae Transmitted by ticks | Cows, sheep, and goats | Sub-Saharan Africa and West Indies | About 5 to 10 days after the bacteria enter the body, symptoms begin. A black scab (eschar) usually develops at the site of the tick bite. | |
Mediterranean spotted fever (boutonneuse fever) | Rickettsia conorii Transmitted by dog ticks | Dogs | Africa, India, southern Europe, and the Middle East around the Mediterranean, Black, and Caspian Seas | About 5 to 7 days after the bacteria enter the body, symptoms begin. A black scab (eschar) may develop at the site of the tick bite. |
Rickettsia sibirica Transmitted by ticks | Rodents | Armenia, central Asia, Siberia, Mongolia, and China | A black scab (eschar) may develop at the site of the tick bite. | |
Rickettsia australis Transmitted by ticks | Rodents | Australia | A black scab (eschar) may develop at the site of the tick bite. | |
Rickettsia parkeri Transmitted by ticks | Rodents | Southern United States and South America | About 2 to 10 days after the bacteria enter the body, symptoms begin. A black scab (eschar) usually develops at the site of the tick bite. | |
Rickettsia akari Transmitted by mites (chiggers) | House mice and some wild mice | United States, Russia, Korea, and Africa | A small bump appears at the site of the mite bite. It develops into a small sore that leaves a scar when it heals. About 1 week later, fever with chills and sweating, headache, muscle pains, and a widespread rash develop. | |
Rickettsia rickettsii subspecies californica (formerly Rickettsia philipii) Transmitted by ticks | Pacific Coast ticks (ticks are both the vectors and the hosts) | California | A black scab (eschar) usually develops at the site of the tick bite, followed by fever, swollen lymph nodes, headache, muscle aches, and fatigue. Rash is a less common than with the other spotted fevers. | |
Neorickettsial infection | ||||
Sennetsu fever | Neorickettsia sennetsu Transmitted by parasitic flatworms | Snails, insects, and fish | Southeast Asia, East Asia, and possibly other regions of Asia | A rash rarely develops. |
Ehrlichiosis | Ehrlichia chaffeensis Transmitted by ticks, mainly the lone star tick | White tail deer and other mammals (such as dogs, raccoons, and opossums) | Southeastern and south central United States | About 9 days after a tick bite, symptoms usually begin. They include sudden fever, chills, muscle aches, weakness, nausea, vomiting, cough, headache, and a general feeling of illness. A rash may develop on the torso, arms, and legs in some people with ehrlichiosis. |
Anaplasmosis | Anaplasma phagocytophilum Transmitted by ticks | Mainly mice and other small rodents | In the United States: The Northeast, mid-Atlantic, upper Midwest, and West Coast Europe | About 9 days after a tick bite, symptoms usually begin. They include sudden fever, chills, muscle aches, weakness, nausea, vomiting, cough, headache, and a general feeling of illness. A rash may develop on the torso, arms, and legs but is not common among people with anaplasmosis. |
Neoehrlichiosis | Neoehrlichia mikurensis Transmitted by ticks | Rodents, including voles and mice | Europe and Asia | Fever, muscle aches, joint pain, and bleeding occur. The rash is violet-colored, raised bumps (nodules) or a shiny, painful, red, raised patch on the skin. |
Q fever | ||||
Coxiella burnetii Transmitted by inhaling infected airborne droplets or dust containing the bacteria or by consuming contaminated raw milk | Sheep, cattle, and goats | Throughout the world | About 2 to 3 weeks after bacteria enter the body, symptoms begin suddenly. They include fever, severe headache, chills, extreme weakness, muscle aches, loss of appetite, sweating, a dry cough, chest pain, and shortness of breath (caused by pneumonia). Q fever causes a rash only in some people who develop an infection of the lining of the heart (endocarditis). | |
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 may develop confusion and severe weakness often with cough, difficulty breathing, and sometimes vomiting.
In scrub typhus (tsutsugamushi disease), a black scab (eschar) forms at the site of a chigger bite (top). A rash develops later (bottom).
Images courtesy of Yoshiki Taniguchi, MD, and the Dermatology Online Journal.
When the infection is advanced, gangrene of the fingers or toes may develop, the liver or spleen may enlarge, the kidneys may malfunction, and blood pressure may fall dangerously low (causing shock). Death can result.
Diagnosis of Rickettsial Infections
A doctor's evaluation
Blood tests
Biopsy of the skin
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 rickettsial infections are common
A bite is a helpful clue, particularly in geographic areas where rickettsial or related infections are common. However, many people do not recall being bitten.
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 such as fever, headache, muscle aches, nausea, vomiting, or stomach pain
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
Testing is usually needed to confirm the diagnosis. Often, doctors need specialized tests to confirm an infection with rickettsiae or rickettsia-like bacteria quickly.
Doctors do two tests to make the bacteria easier to detect and identify:
An immunofluorescence assay is a blood test that detects antibodies to rickettsiae or rickettsia-like bacteria.
The polymerase chain reaction (PCR) technique is used to make copies of the bacteria's DNA, so that the bacteria can be detected more rapidly. This test is done on a blood sample or on a small sample of removed skin that is affected by the rash (biopsy).
Treatment of Rickettsial Infections
Antibiotics
Doctors usually give people antibiotics without waiting for test results. Early treatment of rickettsial infections can prevent complications from developing, reduce the risk of dying, and shorten the recovery time.
Doctors typically give people with a rickettsial infection the antibiotic doxycycline. Doxycycline is usually given by mouth (orally). It is given by vein (intravenously) to people who are very sick.
Although doxycycline can cause tooth staining in children younger than 8 years old, a short, 5- to 10-day course of doxycycline for rickettsial disease in children of all ages is recommended by the American Academy of Pediatrics and can be used without causing tooth staining or weakening of tooth enamel.
After treatment, most people with a mild infection noticeably improve quickly, and fever usually disappears. People take the antibiotic for a minimum of 1 week and sometimes longer if the fever persists or if their infection is severe. When treatment begins late, improvement tends to be slower and the fever lasts longer. If the infection is untreated or if treatment is begun too late, people may die, especially if they have epidemic typhus, scrub typhus, or Rocky Mountain spotted fever.
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