Serologic Evidence of Human Monocytic and Granulocytic Ehrlichiosis in Israel.

To the Editor: We read with great attention the article by Dr. Keysary et al., who reported the first evidence of human monocytic and granulocytic ehrlichiosis in Israel (1); however, we disagree with their conclusions.

Ehrlichiae comprise a large group of intracellular organisms pathogenic for animals and occasionally for humans. Because these organisms are closely related, serologic cross-reactions occur within and between groups, leading to mistakes in identification. For example, Ehrlichia chaffeensis was misdiagnosed as E. canis in humans (2) and human granulocytic ehrlichiosis as human monocytic ehrlichiosis in areas where the vector was not present (3). Because of such cross-reactions, serology alone is not sufficient to establish the existence of a new ehrlichial disease.

With the exception of Rhipicephalus sanguineus, the brown dog tick, which is distributed worldwide, tick species of medical importance are very geographically specific. For example, the Ixodes and Dermacentor spp. found in Europe are not those found in the United States. Consequently, tick-transmitted organisms and diseases are also very specific geographically. For example, Borrelia spp. found in the Old World are not found in America (except for B. burgdorferi stricto sensu, which is found in both Europe and America). R. rickettsii, transmitted by Dermacentor andersoni and D. variablilis, is reported in the United States but not in Europe, where the vectors are not present.

American monocytic ehrlichiosis is caused by E. chaffeensis, which is transmitted by the tick Amblyomma americanum, found only in America. The main reservoir is the deer Odocoileus virginanus (4).

It is very unlikely that a tick-borne disease occurred in a country where neither the vector nor the reservoir of the bacterium exists. All attempts to demonstrate the presence of E. chaffeensis in the Old World, including Africa, have failed. Indeed, there is no convincing evidence of the existence of E. chaffeensis outside America.

References

(1.) Keysary A, Amram L, Keren G, Sthoeger Z, Potasman I, Jacob A, et al. Serologic evidence of human monocytic and granulocytic ehrlichiosis in Israel. Emerg Infect Dis 1999;5:775-8.

(2.) Maeda K, Markowitz N, Hawley RC, Ristic M, Cox D, McDade JE. Human infection with Ehrlichia canis, a leukocytic rickettsia. N Engl J Med 1987;316:853-6.

(3.) Brouqui P, Raoult D. Human ehrlichiosis. N Engl J Med 1994;330:1760-1.

(4.) Dumler JS, Bakken JS. Ehrlichial diseases of humans: emerging tick-borne infections. Clin Infect Dis 1995;20:1102-10.

Philippe Brouqui(*) and J. Steven Dumler([dagger]) Unite des Rickettsies, Faculte de Medecine, Marseille, France; and Johns Hopkins University School of Hygiene & Public Health, Baltimore, Maryland, USA