Ehrlichiosis (air-lik-e-O-sis) is an infectious disease caused by various strains of Ehrlichia (air-LIH-kee-uh) bacteria, transmitted to humans by ticks.
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Caused by an organism once thought to infect only dogs, sheep, cattle, goats, and horses, ehrlichiosis was first discovered in humans in 1953 when researchers in Japan found that Sennetsu fever, an illness that resembles mononucleosis * , was caused by Ehrlichia sennetsu bacteria. Since the 1980s, scientists have identified three additional strains * of Ehrlichia bacteria that cause forms of human ehrlichiosis in the United States: E. chaffeensis, which causes human monocytic ehrlichiosis (HME); bacteria similar or identical to E. phagocytophila or E. equi (known to cause ehrlichiosis in animals), which cause human granulocytic ehrlichiosis (HGE); and E ewingii, which has only been seen in a few patients in the midwestern United States and Tennessee.
What Is Ehrlichiosis?
Ehrlichiosis interferes with the body's immune system by attacking white blood cells, a vital part of the body's defense against invading bacteria, viruses, and other microbes * or harmful substances. Untreated, the disease can leave people vulnerable to other infections.
Ehrlichiosis does not spread from person to person. The Ehrlichia bacteria that cause the disease are spread through tick bites. The species that most commonly spread the disease are the lone star tick, the blacklegged tick, and the western black-legged tick.
Between 1986 and 1997, 1,223 cases of human ehrlichiosis were reported in the United States. Most occurred along the Atlantic Coast and in southern and central states, although cases were reported in almost every region of the country. The number of cases peaks during tick season, which runs from April to October.
What Happens When People Get Ehrlichiosis?
Most cases of ehrlichiosis are associated with mild flulike symptoms, such as fever, chills, headaches, muscle or joint pain, nausea and vomiting, cough, stomach pain, and sore throat. Some people with the infection show no symptoms at all. Symptoms usually start within 2 weeks of a tick bite but can take up to a month to appear.
* mononucleosis (mah-no-nu-klee-O-sis) is an infectious illness caused by a virus that often leads to fever, sore throat, swollen glands, and tiredness.
* strains are subtypes of particular species of organisms, such as viruses or bacteria.
* microbes (MY-krobes) are microscopic living organisms, especially bacteria and viruses.
* Lyme (LIME) disease is a bacterial infection that is spread to humans by the bite of an infected tick. It begins with a distinctive rash and/or flulike symptoms and, in some cases, can progress to a more serious disease with complications affecting other body organs.
* antibodies (AN-tih-bah-deez) are protein molecules produced by the body's immune system to help fight specific infections caused by microorganisms, such as bacteria and viruses.
Because ehrlichiosis shares many symptoms with Lyme disease * and other infections transmitted by ticks, diagnosis based on symptoms alone can be difficult. Blood tests are done to look for evidence of Ehrlichia infection, such as antibodies * to the bacteria or the presence of the germ itself in the blood.
If treated early, ehrlichiosis responds very well to certain antibiotics. Over-the-counter medicine such as acetaminophen (uh-see-teh-MIH-noh-fen) can help lower fever and relieve pain. Usually, people recover from mild cases of ehrlichiosis soon after finishing a week of antibiotic treatment. In severe cases, patients may need treatment in the hospital.
Although many cases of ehrlichiosis are mild, the infection can become serious if it is not treated. Some people who get ehrlichiosis develop anemia * and inflammation of the liver and kidneys. Breathing problems, internal bleeding, brain inflammation (encephalitis, en-seh-fuh-LYE-tis), and seizures * can also develop. People with weakened immune systems, such as those with HIV (human immunodeficiency virus * ) infection, certain types of cancer, or the elderly, tend to develop more severe symptoms and complications. For these people, ehrlichiosis can be fatal.
Can Ehrlichiosis Be Prevented?
Avoiding direct contact with ticks is the best way to prevent ehrlichiosis. Experts recommend that people use tick repellent and wear light-colored, long-sleeved shirts (to help find ticks more easily) and long pants tucked into socks when entering potentially tick-infested areas such as woods or campgrounds. After visiting such areas, it is wise to carefully check the body, clothes, and hair for ticks. Pets need to be checked as well.
* anemia (uh-NEE-me-uh) is a blood condition in which there is a decreased amount of oxygen-carrying hemoglobin in the blood and, usually, fewer than normal numbers of red blood cells.
* seizures (SEE-zhurs) are sudden bursts of disorganized electrical activity that interrupt the normal functioning of the brain, often leading to uncontrolled movements in the body and sometimes a temporary change in consciousness.
* human immunodeficiency (HYOO-mun ih-myoo-no-dih-FIH-shen-see) virus, or HIV, is the virus that causes AIDS (acquired immunodeficiency syndrome), an infection that severely weakens the immune system.
Lyme Disease Foundation, Inc., One Financial Plaza, 18th Floor,
Hartford, CT 06103. The Lyme Disease Foundation offers information on
tick-borne illnesses and avoiding tick bites on its website.
National Center for Infectious Diseases, U.S. Centers for Disease
Control and Prevention, Mailstop C-14, 1600 Clifton Road, Atlanta, GA
30333. The website for this government agency provides information about