ehrlichiosis

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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.

ehr·lich·i·o·sis

(er-lik'ē-ō'sis),
Infection with leukocytic rickettsiae of the genus Ehrlichia; in humans, especially by E. sennetsu that produces manifestations similar to those of Rocky Mountain spotted fever.

ehrlichiosis

/ehr·lich·i·osis/ (ār-lik″e-o´sis) a febrile illness due to infection with bacteria of the genus Ehrlichia.
human granulocytic ehrlichiosis  a sometimes fatal human ehrlichiosis caused by an Ehrlichia equi –like species, characterized by flulike symptoms and involving predominantly neutrophils.
human monocytic ehrlichiosis  a sometimes fatal human ehrlichiosis caused by Ehrlichia chaffeensis, characterized by flulike symptoms and involving predominantly fixed tissue mononuclear phagocytes.

ehrlichiosis

(âr-lĭk′ē-ō′sĭs)
n.
Infection with parasitic rickettsiae of the genus Ehrlichia, especially E. sennetsu, that are transmitted by ticks and produce manifestations in humans similar to those of Rocky Mountain spotted fever, including rash, muscle pain, and fever.

ehrlichiosis

a sometimes fatal tick-borne infection with symptoms similar to those of Lyme disease. The great majority of infections are asymptomatic. Most cases present as mild to moderate acute febrile illness. The disease usually begins about 10 days after the bite of an infected tick, although some cases have begun abruptly, within hours, with influenza-like symptoms, including painful muscle aches, headaches, fever, chills, loss of appetite, and depressed blood cell counts. Although similar to Lyme disease, the infection does not respond to the antibiotics used to treat Lyme disease. However, ehrlichiosis does respond to early treatment with tetracycline antibiotics. The tick that carries the ehrlichiosis infection is the same species as the vector of Lyme disease, Borrelia burgdorferi, but the patient usually recovers within 8 weeks without the chronic arthritis symptoms associated with Lyme disease. Diagnosis is difficult because of the similarities with Lyme disease, and cases of simultaneous infections of both types of bacteria have been reported. Also, one of the organisms associated with ehrlichiosis, Ehrlichia equi, is nearly identical to a bacterium that causes fevers in horses. Also called human granulocytic ehrlichiosis, human monocytic ehrlichiosis. See also Ehrlichia.

ehrlichiosis

Infectious disease A rare tick-borne infection, caused by Ehrlichia canis, that usually affects dogs Clinical Fever, chills, rigors, malaise, nausea, myalgia, anorexia, encephalopathy, acute respiratory failure with infiltrates, acute renal failure with ↑ creatinine Lab ↓ platelets, ↑ transaminases Treatment Chloramphenicol, tetracycline

ehr·lich·i·o·sis

(ār-lik'ē-ō'sis)
A tick-borne infection of humans, dogs, and many other mammals caused by bacteria from the Neorickettsia, Anaplasma, and Ehrlichia groups; produces manifestations similar to those of Rocky Mountain spotted fever.

Ehrlichiosis

A rare human infection with Ehrlichia organisms such as E. canis that normally infect animals. The first known human infection was described in Japan in 1954. The illness is usually acquired by a tick bite and resembles glandular fever (infective mononucleosis). A new species, E. chaffeensis , was isolated in 1991 and a third in 1994. The disease is largely confined to the Southeast and mid-Atlantic states of the USA.

ehr·lich·i·o·sis

(er-lik'ē-ō'sis)
Infection with leukocytic rickettsiae of the genus Ehrlichia; in humans, especially by E. sennetsu, which produces manifestations similar to those of Rocky Mountain spotted fever.

ehrlichiosis, ehrlichosis

disease caused by infection with members of the genus Ehrlichia as well as some former members now in the genera Anaplasma and Neorickettsia.

canine granulocytic ehrlichiosis
infection of neutrophils and rarely eosinophils; usually a milder disease than that caused by E. canis (below) with lameness and joint swelling due to polyarthritis.
canine monocytic ehrlichiosis
caused by Ehrlichia canis which is transmitted by the brown dog tick, Rhipicephalus sanguineus. The disease is characterized by pancytopenia and bleeding tendencies, particularly epistaxis. Called also tropical canine pancytopenia, canine hemorrhagic fever, tracker dog disease, canine rickettsiosis, canine tick typhus, Nairobi bleeding disease, Lahore canine fever.
equine ehrlichiosis
is an infectious disease caused by Anaplasma phagocytophila. The clinical syndrome comprises high fever, hemolytic anemia, incoordination, edema of the extremities and a marked leukopenia. The disease bears a strong resemblance to equine infectious anemia.
equine intestinal ehrlichiosis
a highly fatal enterocolitis of horses caused by Neorickettsiaristicii. Characterized by high fever, leukopenia and acute diarrhea. Called also Potomac horse fever, equine monocytic ehrlichiosis.
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