Healthcare Professionals: Common Ticks
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Ehrlichiosis is the general name used to describe several bacterial diseases that affect animals and humans. Human ehrlichiosis a disease caused by at least three different ehrlichial species in the United States:
- Ehrlichia chaffeensis
- Ehrlichia ewingii
Ehrlichiae are transmitted to humans by the bite of an infected tick. The lone star tick (Amblyomma americanum) is the primary vector of both E. chaffeensis and E. ewingii in Arkansas. Typical symptoms include: fever, headache, fatigue, and muscle aches. Usually, these symptoms occur within 1-2 weeks following a tick bite. Ehrlichiosis is diagnosed based on symptoms, clinical presentation, and later confirmed with specialized laboratory tests. The first line treatment for adults and children of all ages is doxycycline. Ehrlichiosis and other tickborne diseases can be prevented.
Ehrlichiosis was first recognized as a disease in the United States in the late 1980’s, but did not become a reportable disease until 1999. The Arkansas Department of Health conducts surveillance and investigates cases of Ehrlichiosis reported in Arkansas.
- Ehrlichiosis is the second most prevalent tickborne disease in Arkansas, and is found statewide.
- Ehrlichiosis has been found year round in Arkansas with disease peaking from April to September.
In the United States, the term “ehrlichiosis” may be broadly applied to several different infections. Ehrlichia chaffeensis and Ehrlichia ewingii are transmitted by the lonestar tick in the southeastern and south-central United States. The symptoms caused by infection with these Ehrlichia species usually develop 1-2 weeks after being bitten by an infected tick. The tick bite is usually painless, and about half of the people who develop ehrlichiosis may not even remember being bitten by a tick.
The following is a list of symptoms commonly seen with this disease; however, it is important to note that the combination of symptoms varies greatly from person to person.
- Muscle pain
- Conjunctival injection (red eyes)
- Rash (in up to 60% of children, less than 30% of adults)
Ehrlichiosis is a serious illness that can be fatal if not treated correctly, even in previously healthy people. Severe clinical presentations may include difficulty breathing, or bleeding disorders. The estimated case fatality rate (i.e. the proportion of persons who die as a result of their infection) is 1.8%. Patients who are treated early may recover quickly on outpatient medication, while those who experience a more severe course may require intravenous antibiotics, prolonged hospitalization or intensive care.
Skin rash is not considered a common feature of ehrlichiosis, and should not be used to rule in or rule out an infection. E. chaffeensis infection can cause a rash in up to 60% of children, but is reported in fewer than 30% of adults. Rash is not commonly reported in patients infected with E. ewingii. The rash associated with E. chaffeensis infection may range from maculopapular to petechial in nature, and is usually not pruritic (itchy). The rash usually spares the face, but in some cases may spread to the palms and soles. A type of rash called erythroderma may develop in some patients. Erythroderma is a type of rash that resembles sunburn and consists of widespread reddening of the skin that may peel after several days. Some patients may develop a rash that resembles the rash of Rocky Mountain spotted fever making these two diseases difficult to differentiate on the basis of clinical signs alone.
The severity of ehrlichiosis may depend in part on the immune status of the patient. Persons with compromised immunity caused by immunosuppressive therapies (e.g., corticosteroids, cancer chemotherapy, or long-term immunosuppressive therapy following organ transplant), HIV infection, or splenectomy appear to develop more severe disease, and may also have higher case-fatality rates (i.e. the proportion of patients that die from infection.)
Because Ehrlichia organisms infect the white blood cells and circulate in the blood stream, these pathogens may pose a risk to be transmitted through blood transfusions. E. chaffeensis has been shown to survive for more than a week in refrigerated blood. Several instances of suspected E. chaffeensis transmission through solid organ transplant have been investigated, although to date no cases have been confirmed that can be attributed to this route of transmission. Patients who develop ehrlichiosis within a month of receiving a blood transfusion or solid organ transplant should be reported to state health officials for prompt investigation. Use of leukoreduced blood products may theoretically decrease the risk of transfusion-associated transmission of these pathogens. However, the filtration process does not remove all leukocytes or bacteria not associated with leukocytes from leukoreduced blood; therefore, this process may not eliminate the risk completely.
There are several aspects of ehrlichiosis that make it challenging for healthcare providers to diagnose and treat. The symptoms vary from patient to patient and can be difficult to distinguish from other diseases. Treatment is more likely to be effective if started early in the course of disease. Diagnostic tests based on the detection of antibodies will frequently be negative in the first 7-10 days of illness. For this reason, healthcare providers must use their judgment to treat patients based on clinical suspicion alone. Healthcare providers may find important information in the patient’s history and physical examination that may aid clinical suspicion. Information such as recent tick bites, exposure to areas where ticks are likely to be found, or history of recent travel to areas where ehrlichiosis is endemic can be helpful in making the diagnosis.
The healthcare provider should also look at routine blood tests, such as a complete blood cell count or a chemistry panel. Clues such as a low platelet count (thrombocytopenia), low white blood cell count (leukopenia), or elevated liver enzyme levels are helpful predictors of ehrlichiosis, but may not be present in all patients depending on the course of the disease. After a suspect diagnosis is made on clinical suspicion and treatment has begun, specialized laboratory testing should be used to confirm the diagnosis of ehrlichiosis.
The Arkansas Department of Health utilizes the Centers for Disease Control and Prevention (CDC) case definition for Ehrlichiosis. Current case definitions for all tickborne diseases can be found on the National Notifiable Diseases Surveillance System (NNDSS) website.
Doxycycline is the first line treatment for adults and children of all ages and should be initiated immediately whenever ehrlichiosis is suspected. The clinical presentation for ehrlichiosis can resemble other tickborne diseases, such as Rocky Mountain spotted fever and anaplasmosis. Similar to ehrlichiosis, these infections respond well to treatment with doxycycline. Healthcare providers should order diagnostic tests for additional agents if the clinical history and geographic association warrant.
Use of antibiotics other than doxycycline and other tetracyclines is associated with a higher risk of fatal outcome for some rickettsial infections.
- Doxycycline is most effective at preventing severe complications from developing if it is started early in the course of disease. Therefore, treatment must be based on clinical suspicion alone and should always begin before laboratory results return.
- If the patient is treated within the first 5 days of the disease, fever generally subsides within 24-72 hours. In fact, failure to respond to doxycycline suggests that the patient’s condition might not be due to ehrlichiosis. Severely ill patients may require longer periods before their fever resolves. Resistances to doxycycline or relapses in symptoms after the completion of the recommended course have not been documented.
- In cases of life threatening allergies to doxycycline and in some pregnant patients for whom the clinical course of ehrlichiosis appears mild, physicians may need to consider alternate antibiotics. Although recommended as a second-line therapeutic alternative to treat Rocky Mountain spotted fever (RMSF), chloramphenicol is not recommended for the treatment of either ehrlichiosis or anaplasmosis, as studies have shown a lack of efficacy.
- Rifampin appears effective against Ehrlichia in laboratory settings. However, rifampin is not effective in treating RMSF, a disease that may be confused with ehrlichiosis.
- Healthcare providers should be cautious when exploring treatments other than doxycycline, which is highly effective in treating both.
- Broad spectrum antibiotics are not considered highly effective against ehrlichiosis.
- Sulfa drugs during acute illness may worsen the severity of infection.
Doxycycline is the first line treatment for adults and children of all ages:
- Adults: 100 mg every 12 hours
- Children under 45 kg (100 lbs.): 2.2 mg/kg body weight given twice a day
- Patients should be treated for at least 3 days after the fever subsides and until there is evidence of clinical improvement.
- Standard duration of treatment is 7 to 14 days.
- Some patients may continue to experience headache, weakness and malaise for weeks after adequate treatment.
Avoiding being bit by a tick is the best prevention for Ehrlichiosis. Antibiotic treatment following a tick bite is not recommended as a means to prevent Ehrlichiosis. There is no evidence this practice is effective, and this may simply delay onset of disease. For more in-depth information about prevention of tickborne disease, please visit our Prevention of Mosquito and Tickborne Disease section. Additional information on tickborne disease can be found at CDC’s Division of Vector-Borne Diseases (DVBD) webpage.