Medication Summary
The drug of choice for infections with human monocytic ehrlichiosis (HME) and human granulocytic anaplasmosis (HGA) in both adults and children is doxycycline. It is also the recommended drug for many other tick-borne infections, such as Rocky Mountain spotted fever.
Early initiation of doxycycline should be done once there is a high index of suspicion of either human monocytic ehrlichiosis (HME) or human granulocytic anaplasmosis (HGA as delay in treatment is usually associated with increased morbidity especially in immunocompromised hosts. Supportive management such as antipyretics, hydration with intravenous fluids, should also be initiated if indicated.
The American Academy of Pediatrics recommends a short course of doxycycline (< 21 days) as first-line therapy for severe/life threatening suspected or proven HGA and HME in children of all ages. Tetracyclines in general are known to cause teeth discoloration in young children, however, this risk is minimal if a short course of doxycycline is used. [17]
Doxycycline can be administered intravenously in patients who are very sick and are unable to tolerate oral medications or given orally in less sick patients who can tolerate pills. Dose is usually 100mg every 12 hours for a duration of 7 to 10 days or continued for 3 to 5 days after resolution of fever in adults or for 7 to 14 days in children. Treatment should be continued for at least 3 days after resolution of fever. [18, 19]
For patients who are intolerant or have severe allergy to doxycycline, rifampin and chloramphenicol are alternative treatment options.
Rifampin has been used as an alternative agent in both adults and children and even in pregnant women. Children treated with rifampin will need closer monitoring. [18]
There is limited data about the use of Chloramphenicol in this setting although it has been used in a few instances but given its hematological adverse effects, it is usually avoided. Oral chloramphenicol is not readily available in most pharmacies in the United States.
Prophylaxis
Currently, there is no recommendation for the use of doxycycline or other antibiotics for post tick exposure prophylaxis against HME or HGA. Individuals with potential tick-bite exposure should monitor for development of symptoms such as feeling unwell, fever, new rash within 2 weeks of exposure and contact their healthcare providers for further evaluation.
Antibiotics
Class Summary
Empiric antimicrobial therapy should cover the most likely pathogens in the context of the clinical setting.
Doxycycline (Vibramycin, Doryx, Adoxa)
This is a second-generation tetracycline. It is more active than tetracycline against many pathogens. Doxycycline has different pharmacokinetics and a different adverse effect profile from tetracycline.
Doxycycline inhibits protein synthesis and thus bacterial growth by binding with 30S and, possibly, 50S ribosomal subunits of susceptible bacteria.
Rifampin (Rifadin)
Rifampin inhibits ribonucleic acid (RNA) synthesis in bacteria by binding to the beta subunit of deoxyribonucleic acid (DNA)-dependent RNA polymerase, which, in turn, blocks RNA transcription.
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Female Lone Star tick, Amblyomma americanum, found in the southeastern and Midatlantic United States. It is a vector of several zoonotic diseases, including human monocytic ehrlichiosis and Rocky Mountain spotted fever. Courtesy of the CDC/Michael L. Levin, PhD.
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Map of the United States showing the distribution of the Lone Star Tick, which is the principle vector for ehrlichiosis.
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Established and reported distribution of anaplasmosis vectors Ixodes scapularis and Ixodes pacificus, by county, in the United States from 1907-1996. Courtesy of the Division of Vector-Borne Infectious Diseases at the Centers for Disease Control and Prevention.
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Anaplasmosis incidence by age. Courtesy of the Centers for Disease Control and Prevention.
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Ehrlichiosis incidence by age. Courtesy of the Centers for Disease Control and Prevention.
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This graph displays the number of human cases of ehrlichiosis caused by Ehrlichia chaffeensis reported to the Centers for Disease Control and Prevention (CDC) annually from 2000 through 2016. *From 2000 to 2008, ehrlichiosis was included in the reporting category “human monocytic ehrlichiosis” in reports to the National Notifiable Diseases Surveillance System (NNDSS). **Since 2008, ehrlichiosis has been reported to the NNDSS under the categories “Ehrlichia chaffeensis infections,” “Ehrlichia ewingii infections,” and “Undetermined ehrlichiosis/anaplasmosis infections”, which include infections caused by Ehrlichia muris eauclairensis. Only E chaffeensis infections are shown above. Courtesy of the CDC (https://www.cdc.gov/ehrlichiosis/stats/index.html).
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This graph shows the number of ehrlichiosis cases caused by Ehrlichia chaffeensis reported from 2000 through 2016 by month of onset to illustrate the seasonal trends. Cases are reported in each month of the year, although most are reported in June and July. Courtesy of the CDC (https://www.cdc.gov/ehrlichiosis/stats/index.html).
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This graph shows the number of US ehrlichiosis cases caused by Ehrlichia chaffeensis and reported to the CDC from 2000 to 2018. Courtesy of the CDC (https://www.cdc.gov/ehrlichiosis/stats/).
Tables
|
Human monocytic ehrlichiosis (HME) |
Human granulocytic anaplasmosis (HGA) |
Cell type Affected |
Monocytes |
Granulocytes |
Organism |
E chaffeensis |
A phagocytophilum |
Vector |
Amblyomma americanum (Lone Star tick) |
Ixodes scapularis (black-legged tick), Ixodes pacificus (Western black-legged tick) in California, Ixodes ricinus in Europe, and probably Ixodes persulcatus in parts of Asia |
Location |
Southeastern and south-central United States |
Wisconsin and Minnesota, less active in New York and Connecticut, also California |
Rash |
30% of adults, 60% of children |
Rare |
Prognosis |
~3% mortality |
< 1% mortality |
