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Ehrlichiosis is an infectious disease transmitted by the bite of a tick, first described in 1990; the two specific organisms that have been implicated are Ehrlichia chaffeensis and granulocytic Ehrlichia.
Causes & Development; Risk Factors
The Ehrlichia bacteria belong to the family Rickettsiae. Rickettsial organisms are responsible for a number of serious diseases with worldwide distribution, such as Rocky Mountain spotted fever, typhus, murine typhus, scrub typhus, Queensland tick typhus, Boutonneuse fever, North Asian tick-borne rickettsiosis, rickettsial pox, and others. All of these diseases require an insect vector (tick, flea, mite) to transmit them to humans or other animals.
The infectious organism of ehrlichiosis is transmitted to humans by the bite of ticks. Rickettsiae are often associated with a specific tick: Ehrlichia inhabit the Lone Star tick (Amblyomma americanum), the American dog tick (Dermacentor variabilis), and the deer ticks (Ixodes dammini and Ixodes scapularis). Note that the deer tick is also the carrier of Lyme disease. The main geographic areas where ehrlichiosis is found in the United States are the southern central states and southern Atlantic states. It has recently been reported in the upper midwestern region.
Risk factors for ehrlichiosis include living in an area with a lot of ticks, passing through high grasses, and owning a pet that may bring ticks home.
Signs & Symptoms
The incubation period for ehrlichiosis is approximately 9 days from the time of tick bite. Ehrlichiosis begins with fever, chills, headache, muscle pain (myalgia), and nausea. A maculopapular or petechial rash appears in over half the cases and the disease may be mistaken for Rocky Mountain spotted fever. The symptoms are often quite general, but the infected individual is sometimes sick enough to seek medical attention. Surveys show that the majority of people exposed do not seek treatment and likely never knew they were infected.
Symptoms include:- fever
- chills
- headache
- nausea
- muscle aches (myalgia)
- malaise
- rash, maculopapular
- rash, petechial
Diagnosis & Tests
A CBC shows decreased white blood cells (leukopenia), decreased platelets (thrombocytopenia); a granulocyte stain shows clumps of bacteria inside white blood cells; the platelet count shows decreased platelets (thrombocytopenia); liver enzymes show elevated transaminase; a fluorescent antibody test may turn positive for E. chaffeensis or granulocytic Ehrlichia.
Treatment & Prevention
Preventing tick bites will prevent Ehrlichiosis and other tick-borne diseases. Common measures include the use of insect repellent, appropriate clothing, sticking to trails and avoiding dense brush when hiking, and not standing under overhanging foliage. After hiking or outings in the woods it is a good idea to examine yourself for ticks and remove any that may be found. Studies suggest that a tick must be attached for at least 24 hours in order to cause disease, so early removal can prevent infection. The date and time of a tick bite should be recorded because the incubation period of some tick-borne diseases is long enough (the incubation period for Lyme disease is up to 1 month) that the event could be forgotten.
Prognosis
Some patients may recover on their own, but Ehrlichiosis can be fatal.
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Signs, symptoms & indicators of Ehrlichiosis:
Conditions that suggest Ehrlichiosis:
Recommendations and treatments for Ehrlichiosis: | | | | | Drug |  Antibiotics | The organism is sensitive to antibiotics and treatment results in improvement in 24 to 48 hours. Recovery takes 3 weeks. Antibiotics that work for Lyme do not work against Ehrlichiosis. Instead, doctors use drugs in the tetracycline family. Tetracycline drugs can be used against Lyme, so some doctors cover both bases by prescribing tetracycline when the diagnosis is unclear. |
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KEY | | Weak or unproven link | | | Highly recommended |
GLOSSARY
Antibody (Antibodies)
A type of serum protein (globulin) synthesized by white blood cells of the lymphoid type in response to an antigenic (foreign substance) stimulus. Antibodies are complex substances formed to neutralize or destroy these antigens in the blood. Antibody activity normally fights infection but can be damaging in allergies and a group of diseases that are called autoimmune diseases.
Bacteria (Bacterial, Bacterium)
Microscopic germs. Some bacteria are "harmful" and can cause disease, while other "friendly" bacteria protect the body from harmful invading organisms.
Complete Blood Count (CBC)
A set of measurements that are generally determined by specially designed machines that analyze the different components of blood in less than a minute. The values generally included are:- White blood cell count (WBC). The number of white blood cells in a volume of blood. Normal range varies slightly between laboratories but is generally between 4,300 and 10,800 cells per cubic millimeter. This can also be referred to as the leukocyte count and can be expressed in international units as 4.3 - 10.8 x 10^9 cells per liter.
- Automated white cell differential. A machine-generated percentage of the different types of white blood cells, usually split into granulocytes, lymphocytes, monocytes, eosinophils, and basophils.
- Red cell count (RBC). The number of red blood cells in a volume of blood. Normal range varies slightly between laboratories but is generally between 4.2 - 5.9 million cells per cubic millimeter. This can also be referred to as the erythrocyte count and can be expressed in international units as 4.2 - 5.9 x 10^12 cells per liter.
- Hemoglobin (Hb). The amount of hemoglobin in a volume of blood. Normal range for hemoglobin is different between the sexes and is approximately 13 - 18 gm/dl for men and 12 - 16 for women (international units 8.1 - 11.2 millimoles/liter for men, 7.4 - 9.9 for women).
- Hematocrit (Hct). The ratio of the volume of red cells to the volume of whole blood. Normal range for hematocrit is different between the sexes and is approximately 45 - 52% for men and 37 - 48% for women.
- Mean cell volume (MCV). The average volume of a red cell. This is a calculated value derived from the hematocrit and red cell count. Normal range is 86 - 98 femtoliters.
- Mean cell hemoglobin (MCH). The average amount of hemoglobin in the average red cell. This is a calculated value derived from the measurement of hemoglobin and the red cell count. Normal range is 27 - 32 picograms.
- Mean cell hemoglobin concentration (MCHC). The average concentration of hemoglobin in a given volume of red cells. This is a calculated volume derived from the hemoglobin measurement and the hematocrit. Normal range is 32 - 36%.
- Red cell distribution width (RDW). A measurement of the variability of red cell size. Higher numbers indicate greater variation in size. Normal range is 11 - 15.
- Platelet count. The number of platelets in a volume blood. Platelets play a vital role in blood clotting. Normal range varies slightly between laboratories but is in the range of 150,000 - 400,000 per cubic millimeter (150 - 400 x 10^9 per liter).
Enzymes (Enzyme)
Specific protein catalysts produced by the cells that are crucial in chemical reactions and in building up or synthesizing most compounds in the body. Each enzyme performs a specific function without itself being consumed. For example, the digestive enzyme amylase acts on carbohydrates in foods to break them down.
Granulocyte (Granulocytes)
A mature white blood cell with cytoplasm containing granules.
Leukopenia
A condition in which the number of white blood cells circulating in the blood is abnormally low.
Liver (Hepatic)
The largest and one of the most complex organs of the body, the liver is responsible for much of the metabolism of fats, proteins and carbohydrates. It is the site of much of the body's detoxification. It is connected very closely with digestion and the regulation of blood sugar, among many other functions. Found behind the ribs on the right side of the abdomen, it has many important functions such as removing harmful material from the blood, making enzymes and bile that help digest food, and converting food into substances needed for life and growth. Hepatic: Pertaining to the liver.
Maculopapular
The term for a rash that contains both macules and papules. A macule is a flat discolored area of the skin, and a papule is a small raised bump. A maculopapular rash is usually a large area that is red, and has small bumps that blend together.
Malaise
A vague feeling of bodily discomfort, as at the beginning of an illness. A general sense of depression or unease.
Myalgia
Diffuse muscle pain.
Nausea
Symptoms resulting from an inclination to vomit.
Petechial
Fine, pinhead-sized hemorrhages on the skin.
Platelets (Platelet)
Cells that help the blood to clot.
Thrombocytopenia
Condition of abnormally small number of platelets circulating in the blood, characterized by inability to properly clot blood and easy bruising.
White Blood Cell (WBC, White Blood Cells)
A blood cell that does not contain hemoglobin: a blood corpuscle responsible for maintaining the body's immune surveillance system against invasion by foreign substances such as viruses or bacteria. White cells become specifically programmed against foreign invaders and work to inactivate and rid the body of a foreign substance. White blood cells are composed primarily of neutrophils, monocytes and lymphocytes. Lymphocytes are either T-cells or B-cells. T-cells (CD3 cells) are divided into T-helper (CD4 cells) and T-suppressor/cytotoxic (CD8 cells) cells.
Last updated: Apr 13, 2008
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