Ehrlichiosis

Ehrlichiosis refers to several tick-borne diseases caused by very small organisms called Ehrlichiae, which affect both humans and animals. Ehrlichiae are gram negative bacteria that infect and destroy white blood cells. Two human diseases are caused by varieties of Ehrlichiae found in the U.S.

• Human monocyte ehrlichiosis (HME) infects white cells known as monocytes. More than 1000 cases of HME have been reported since it was first identified in 1986. It is caused by the bacterium Ehrlichiachaffeensis and is carried by the Lone Star tick, found primarily in the southcentral and southeastern U.S.
• Human granulocytic ehrlichiosis (HGE) infects granulocyte white blood cells. It is more likely than HME to be carried by adult Ixodes ticks and so is most often found northeastern and upper midwestern states.

Ehrlichiosis caused by other or unspecified organisms is a new category that was added in 2000 to account for other cases of these bacteria that have been detected.

Both HGE and HME have been reported in Europe. In fact, a Swedish study reported an almost equal prevalence of ehrlichiosis and Lyme disease in one population group. The European form of HGE appears to be a less severe condition than in the U.S. HME has also been reported in Africa.

Some studies indicate that middle-aged and elderly men are most likely to be infected with either form of ehrlichiosis.

Symptoms of Ehrlichiosis

Ehrlichiosis usually develops rapidly. Patients who are infected with ehrlichiosis will begin to feel symptoms between 3 to 16 days after being bitten by an infected tick. A patient may feel fine early in the day only to experience very severe, debilitating symptoms a few hours later. While ehrlichiosis is often very mild, with only flu-like symptoms, in some cases, symptoms can be severe:

• Rash -- about one-third of HME patients and a smaller proportion of HGE patients develop a rash; the rash does not form a circle as it does in Lyme disease
• Fever

Other common symptoms may include:

• Malaise
• Confusion
• Severe headache
• Muscle and joint aches
• Chills
• Cough
• Nausea, vomiting, and lack of appetite

In serious cases, the patients may develop mental abnormalities, breathing difficulties, and kidney problems. Symptoms that affect the central nervous system, including seizures, coma, a stiff neck, sensitivity to light, and others, may be mistaken for meningitis. There does not appear to be a chronic phase for the ehrlichiosis, although much is still unknown about the disease.

Outlook and Complications of Ehrlichiosis

Some experts estimate that only about 10% of people infected with ehrlichiosis develop symptoms, which are often so mild and flu-like that probably many people recover without seeking either a diagnosis or treatment. In symptomatic patients, however, ehrlichiosis can be more severe than Lyme disease. In studies of reported cases of both HME and HGE, 57 - 62% percent of patients required hospitalization, and estimated morality rates were 5% for HME and 10% for HGE. These percentages, however, probably reflect an overrepresentation of serious cases, and there is some evidence that they are significantly lower (2.7% for HME and 0.7% for HGE). The accuracy of any figures relating to ehrlichiosis is uncertain because there are so few cases.

In general, it is important to initiate treatment for ehrlichiosis as soon as possible. The longer a patient is untreated, the worse the outcome will be. The disease is more severe in the elderly, those with anemia, and people with impaired immune systems such as those with AIDS. HME may be more severe in children because initial symptoms are often mild and even doctors are often unaware of it. The following are severe complications associated with ehrlichiosis when left untreated:

• Either form of ehrlichiosis can damage white-blood cells to the point where a patient can die from serious infections such as fungal pneumonia.
• HGE may infect young white blood cells in the bone marrow, which are then released into general circulation. Infected white blood cells can affect in the spleen, liver, lymph nodes, bone marrow, lung, kidney, and cerebrospinal fluid.
• Signs of central nervous system abnormalities, such as changes in mental state, are indicators of a very dangerous condition.

Ehrlichiosis does not appear to have a chronic phase as Lyme disease does, although blood tests of patients previously treated indicates that the infection persists in many cases. At this time not enough is known about ehrlichiosis to come to any confident conclusions about long-term effects.

Diagnosing Ehrlichiosis

A diagnosis of HME or HGE is based on observation of the patient's symptoms, usually supported by immunofluorescence assay or polymerase chain reaction tests. Few doctors, however, are aware of ehrlichiosis, and even the knowledgeable ones are unable to diagnose ehrlichiosis simply on the basis of symptoms. Experts suggest that doctors consider a diagnosis for ehrlichiosis in the following patients:

• Those with fever and flu-like symptoms who report being bitten by a tick
• Those whose blood tests indicate lower amounts of white blood cells and platelets and elevated liver enzyme levels

During the convalescent stage of ehrlichiosis, blood samples can be examined for antibodies to the organism, but even these are positive in only 80 - 87% of cases of HME. Researchers are currently working on laboratory tests to facilitate more precise diagnoses of ehrlichiosis.

Treating Ehrlichiosis

When treated early, ehrlichiosis responds very well to the antibiotics tetracycline, doxycycline, and rifampin. Some experts report that it is effectively treated for a minimum course of 5 to 7 days. If ehrlichiosis goes untreated, however, it can escalate into a life-threatening condition.

Unfortunately, it does not respond to most of the antibiotics commonly used for Lyme disease, including ampicillin, ceftriaxone, erythromycin, ciprofloxacin, and azithromycin. It is important, then, if ehrlichiosis is at all suspected, to give patients antibiotics, most often doxycycline, that are effective against both tick-derived diseases.