Letter to the Editor

Acute Infection with Human Monocytic Ehrlichiosis: The Tip of the Iceberg?

Authors: Raphael B. Stricker, MD, Elizabeth L. Maloney, MD

Abstract

To the Editor:


In their excellent case report of human monocytic ehrlichiosis (HME), Prince et al1 describe the difficulty in diagnosing this potentially life-threatening tick-borne disease. In the accompanying editorial, Openshaw and Swerdlow2 mention that, in contrast to the fulminant presentation in the case report, HME infection may be “asymptomatic.” This statement deserves further comment.


Although transmission of Ehrlichia chaffeensis, the agent of HME, has primarily been associated with Amblyomma ticks, this organism has also been identified in Ixodes ticks that carry Borrelia burgdorferi, the spirochetal agent of Lyme disease.3 Conversely, Borrelial DNA has been isolated in Amblyomma ticks, which appear to transmit the “Lyme-like” condition known as southern tick-associated rash illness (STARI).4 Deer serve as a reservoir for both Amblyomma and Ixodes ticks and, as mentioned by Openshaw and Swerdlow, the deer population in the United States has increased from about 500,000 in the year 1900 to more than 35 million in the year 2000, with a proportionately increased risk of contracting Lyme disease and HME.5 Migratory birds may also play a prominent role in dissemination of these tick-borne illnesses.6

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References

1. Prince LK, Shah AA, Martinez LJ, et al. Ehrlichiosis: making the diagnosis in the acute setting. South Med J 2007;100:825–828.
 
2. Openshaw JJ, Swerdlow DL. Human ehrlichiosis: clinical and ecological challenges. South Med J 2007;100:769–770.
 
3. Holden K, Boothby JT, Anand S, et al. Detection of Borrelia burgdorferi, Ehrlichia chaffeensis, and Anaplasma phagocytophilum in ticks (Acari: Ixodidae) from a coastal region of California. J Med Entomol 2003;40:534–9.
 
4. Phillips SE, Burrascano JJ, Harris NS, et al. Rash decisions about southern tick-associated rash illness and Lyme disease. Clin Infect Dis 2006;42:306–307.
 
5. Stricker RB. Counterpoint: Long-term antibiotic therapy improves persistent symptoms associated with Lyme disease. Clin Infect Dis 2007;45:149–157.
 
6. Alekseev AN, Dubinina HV, Semenov AV, et al. Evidence of ehrlichiosis agents found in ticks (Acari: Ixodidae) collected from migratory birds. J Med Entomol 2001;38:471–474.
 
7. Dumler JS, Sutker WL, Walker DH. Persistent infection with Ehrlichia chaffeensis. Clin Infect Dis 1993;17:903–905.