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.
· Human granulocytic ehrlichiosis (HGE) infects granulocyte white blood cells.
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 and even cause death.
About one-third of HME patients and a smaller proportion of HGE patients develop a rash. Other common symptoms may include:
- Severe headache
- Muscle and joint aches
- Nausea, vomiting, and lack of appetite
- mental confusion
- systolic murmurs
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, and others, may be mistaken for meningitis.
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. I
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.
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.
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.
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.
For people with Lyme disease, if treatment is not successful then ehrlichiosis must be considered.