Ehrlichiosis

Ehrlichiosis is a tick-borne[1] bacterial infection,[2] caused by bacteria of the family Anaplasmataceae, genera Ehrlichia and Anaplasma. These obligate intracellular bacteria infect and kill white blood cells.

Ehrlichiosis
SpecialtyInfectious disease 

The average reported annual incidence is on the order of 2.3 cases per million people.[3]

Types

Five (see note below) species have been shown to cause human infection:[4]

The latter two infections are not well studied.


In 2008, human infection by a Panola Mountain (in Georgia, USA) Ehrlichia species was reported.[5] On August 3, 2011, infection by a yet-unnamed bacterium in the genus Ehrlichia was reported, carried by deer ticks and causing flu-like symptoms in at least 25 people in Minnesota and Wisconsin. Until then, human ehrlichiosis was thought to be very rare or absent in both states.[6] The new species, which is genetically very similar to an Ehrlichia species found in Eastern Europe and Japan called E. muris, was identified at a Mayo Clinic Health System hospital in Eau Claire.[6]

Ehrlichia species are transported between cells through the host-cell filopodia during the initial stages of infection; whereas, in the final stages of infection, the pathogen ruptures the host cell membrane.[7]

Signs and symptoms

The most common symptoms include headache, muscle aches, and fatigue. A rash may occur, but is uncommon. Ehrlichiosis can also blunt the immune system by suppressing production of TNF-alpha, which may lead to opportunistic infections such as candidiasis.

Most of the signs and symptoms of ehrlichiosis can likely be ascribed to the immune dysregulation that it causes. A "toxic shock-like" syndrome is seen in some severe cases of ehrlichiosis. Some cases can present with purpura and in one such case, the organisms were present in such overwhelming numbers that in 1991, Dr. Aileen Marty of the AFIP was able to demonstrate the bacteria in human tissues using standard stains, and later proved that the organisms were indeed Ehrlichia using immunoperoxidase stains.[8]

Experiments in mouse models further support this hypothesis, as mice lacking TNF-alpha I/II receptors are resistant to liver injury caused by Ehrlichia infection.[9]

About 3% of human monocytic ehrlichiosis cases result in death; however, these deaths occur "most commonly in immunosuppressed individuals who develop respiratory distress syndrome, hepatitis, or opportunistic nosocomial infections."[10]

Prevention

No human vaccine is available for ehrlichiosis. Tick control is the main preventive measure against the disease. However, in late 2012, a breakthrough in the prevention of canine monocytic ehrlichiosis was announced when a vaccine was accidentally discovered by Prof. Shimon Harrus, Dean of the Hebrew University of Jerusalem's Koret School of Veterinary Medicine.[11]

Treatment

Doxycycline and minocycline are the medications of choice. For people allergic to antibiotics of the tetracycline class, rifampin is an alternative.[3] Early clinical experience suggested that chloramphenicol may also be effective, but in vitro susceptibility testing revealed resistance.

Epidemiology

Ehrlichiosis is a nationally notifiable disease in the United States. Cases have been reported in every month of the year, but most cases are reported during April–September.[12][13][14] These months are also the peak months for tick activity in the United States.

From 2008-2012, the average yearly incidence of ehrlichiosis was 3.2 cases per million persons. This is more than twice the estimated incidence for 2000-2007.[14] The incidence rate increases with age, with the ages of 60–69 years being the highest age-specific years. Children less than 10 years and adults aged 70 years and older have the highest case-fatality rates.[14] A documented higher risk of death exists among persons who are immunosuppressed.[12]

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See also

References
  1. "Ehrlichiosis". Division of Vector-Borne Diseases (DVBD), National Center for Emerging and Zoonotic Infectious Diseases (NCEZID), Centers for Disease Control and Prevention. 15 November 2013.
  2. Dawson, Jacqueline E.; Marty, Aileen M. (1997). "Ehrlichiosis". In Horsburgh, C.R.; Nelson, A.M. (eds.). Pathology of emerging Infections. 1. American Society for Microbiology Press. ISBN 1555811205.
  3. Goddard J (September 1, 2008). "What Is New With Ehrlichiosis?". Infections in Medicine.
  4. Dumler JS, Madigan JE, Pusterla N, Bakken JS (July 2007). "Ehrlichioses in humans: epidemiology, clinical presentation, diagnosis, and treatment". Clin. Infect. Dis. 45 (Suppl 1): S45–51. doi:10.1086/518146. PMID 17582569.
  5. Reeves WK, Loftis AD, Nicholson WL, Czarkowski AG (2008). "The first report of human illness associated with the Panola Mountain Ehrlichia species: a case report". Journal of Medical Case Reports. 2: 139. doi:10.1186/1752-1947-2-139. PMC 2396651. PMID 18447934.
  6. Steenhuysen, J. (3 August 2011). "New tick-borne bacterium found in upper Midwest". Reuters. Archived from the original on 2012-06-09.
  7. Thomas S, Popov VL, Walker DH (2010). Kaushal D (ed.). "Exit Mechanisms of the Intracellular Bacterium Ehrlichia". PLoS ONE. 5 (12): e15775. Bibcode:2010PLoSO...515775T. doi:10.1371/journal.pone.0015775. PMC 3004962. PMID 21187937.
  8. Marty AM, Dumler JS, Imes G, Brusman HP, Smrkovski LL, Frisman DM (August 1995). "Ehrlichiosis mimicking thrombotic thrombocytopenic purpura. Case report and pathological correlation". Hum. Pathol. 26 (8): 920–5. doi:10.1016/0046-8177(95)90017-9. PMID 7635455.
  9. McBride JW, Walker DH (2011). "Molecular and cellular pathobiology of Ehrlichia infection: targets for new therapeutics and immunomodulation strategies". Expert Rev Mol Med. 13: e3. doi:10.1017/S1462399410001730. PMC 3767467. PMID 21276277.
  10. Thomas, Rachael J; Dumler, J Stephen; Carlyon, Jason A (1 August 2009). "Current management of human granulocytic anaplasmosis, human monocytic ehrlichiosis and ehrlichiosis". Expert Review of Anti-infective Therapy. 7 (6): 709–722. doi:10.1586/eri.09.44. PMC 2739015. PMID 19681699.
  11. Rudoler N, Baneth G, Eyal O, van Straten M, Harrus S (December 2012). "Evaluation of an attenuated strain of Ehrlichia canis as a vaccine for canine monocytic ehrlichiosis". Vaccine. 31 (1): 226–33. doi:10.1016/j.vaccine.2012.10.003. PMID 23072894.
  12. Dahlgren FS, Heitman KN, Drexler NA, Massung RF, Behravesh CB. Human granulocytic anaplasmosis in the United States from 2008 to 2012: a summary of national surveillance data. Am J Trop Med Hyg 2015;93:66–72.
  13. Drexler NA, Dahlgren FS, Heitman KN, Massung RF, Paddock CD, Behravesh CB. National surveillance of spotted fever group rickettsioses in the United States, 2008–2012. Am J Trop Med Hyg 2016;23–34.
  14. Nichols KH, Dahlgren FS, Drexler NA, Massung RF, Behravesh CB. Increasing incidence of ehrlichiosis in the United States: a summary of national surveillance of Ehrlichia chaffeensis and Ehrlichia ewingii infections in the United States, 2008–2012. Am J Trop Med Hyg 2016;94:52–60.
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