Ehrlichiosis

Definition

Ehrlichiosis is a bacterial infection that is spread by ticks. Symptoms include fever, chills, headache, muscle aches, and tiredness.

Description

Ehrlichiosis is a tick-borne disease caused by infection with Ehrlichia bacteria. Ticks are small, blood-sucking arachnids. Although some ticks carry disease-causing organisms, most do not. When an animal or person is bitten by a tick that carries bacteria, the bacteria are passed to that person or animal during the tick's feeding process. It is believed that the tick must remain attached to the person or animal for at least 24 hours to spread the infection.

There are two forms of ehrlichiosis in the United States; human monocytic ehrlichiosis and human granulocytic ehrlichiosis. Monocytic ehrlichiosis is caused by Ehrlichia chaffeensis, which is spread by the Lone Star tick, Amblyomma americanum. As of early 1998, about 400 cases of monocytic ehrlichiosis had been reported in 30 states, primarily in the southeastern and south central United States. The bacteria that causes granulocytic ehrlichiosis is not known, but suspected to be either Ehrlichia equi or Ehrlichia phagocytophila. Granulocytic ehrlichiosis is probably spread by the blacklegged tick Ixodes scapularis (which also spreads Lyme disease ). About 100 cases of granulocytic ehrlichiosis have been reported in Connecticut, Massachusetts, Rhode Island, Minnesota, New York, and Wisconsin.

Causes and symptoms

Both forms of ehrlichiosis have similar symptoms, and the illnesses can range from mild to severe and life-threatening. Risk factors include old age and exposure to ticks through work or recreation. Symptoms occur seven to 21 days following a tick bite although patients may not recall being bitten. Fever, tiredness, headache, muscle aches, chills, loss of appetite, confusion, nausea, and vomiting are common to both diseases. A rash may occur.

Diagnosis

Ehrlichiosis may be diagnosed and treated by doctors who specialize in blood diseases (hematologists) or an infectious disease specialist. Because ehrlichiosis is not very common and the symptoms are not unique, it may be misdiagnosed. A recent history of a tick bite is helpful in the diagnosis. Blood tests will be done to look for antibodies to Ehrlichia. Staining and microscopic examination of the blood sample may show Ehrlichia bacteria inside white blood cells. Another test, called polymerase chain reaction (PCR), is a very sensitive assay to detect bacteria in the blood sample, but it is not always available.

Treatment

Antibiotic treatment should begin immediately if ehrlichiosis is suspected, even if laboratory results are not available. Treatment with either tetracycline (Sumycin, Achromycin V) or doxycycline (Monodox, Vibramycin) is recommended. Many patients with ehrlichiosis are admitted to the hospital for treatment.

Prognosis

For otherwise healthy people, a full recovery is expected following treatment for ehrlichiosis. Elderly patients are at a higher risk for severe disease, which may be fatal. Serious complications include lung or gastrointestinal bleeding. Two to 10 patients out of 100 die from the disease.

Prevention

The only prevention for ehrlichiosis is to minimize exposure to ticks by staying on the trail when walking through the woods, avoiding tall grasses, wearing long sleeves and tucking pant legs into socks, wearing insect repellent, and checking for ticks after an outing. Remove a tick as soon as possible by grasping the tick with tweezers and gently pulling.

KEY TERMS

Tick-borne disease— A disease that is spread to animals by the bite of an infected tick.

Resources

BOOKS

McDade, Joseph E., and James G. Olsen. "Ehrlichiosis, Q Fever, Typhus, Rickettsialpox, and Other Rickettsioses." In Infectious Diseases. 2nd ed. Philadelphia: W. B. Saunders Co., 1998.

ehrlichiosis , any of several diseases caused by rickettsia of the genus Ehrlichia. Ehrlichiosis is transmitted by ticks. Both human forms tend to develop about nine days after a tick bite. Symptoms include severe headache and chills and low white blood cell and platelet counts. The lack of a rash distinguishes them from Rocky Mountain spotted fever and Lyme disease ; lack of upper respiratory and gastrointestinal symptoms distinguishes them from influenza . Many cases are mild, and all are treatable with antibiotics (tetracycline and doxycycline); however, ehrlichiosis can be fatal in some cases when diagnosis and treatment are delayed.

It was known for years that certain species (some believe them to be variant strains of a single species) can cause disease in animals, for example E. canis in dogs and E. phagocytophila in sheep and cattle. In the mid-1980s human ehrlichiosis was first recognized. The causative agent was found to be E. chaffeensis. This form is now known as human monocytic ehrlichiosis. In 1990 another form of the disease, human granulocytic ehrlichiosis, was identified. The Ehrlichia organisms invade various white blood cells (see blood ; immunity ). E. chaffeensis invades monocytes; granulocytic Ehrlichia invades granulocytes.

Ehrlichiosis

What Is Ehrlichiosis?

What Happens When People Get Ehrlichiosis?

Can Ehrlichiosis Be Prevented?

Resources

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.

KEYWORDS

for searching the Internet and other reference sources

Arthropod-borne infections

Ehrlichia sennetsu

Lyme disease

Rickettsial infections

Sennetsu fever

Tick-borne infections

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.

*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.

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.

*microbes

(MY-krobes) are microscopic living organisms, especially bacteria and viruses.

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 black-legged 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.

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.

*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.

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.

*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.

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.

Resources

See also

Lyme Disease

Mononucleosis, Infectious

Rickettsial Infections

Rocky Mountain Spotted Fever

Tick-borne Infections

Organizations

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.

Telephone 860-525-2000 http://www.lyme.org

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 ehrlichiosis.

Telephone 800-311-3435 http://www.cdc.gov/ncidod