Volume 4, Number 4—December 1998
Dual Infection with Ehrlichia chaffeensis and a Spotted Fever Group Rickettsia: A Case Report
To the Editor: In their article, Daniel J. Sexton et al. state, "Well- documented cases of simultaneous human infections with more than one tick-borne pathogen are rare" (1) and mention only two reports of such cases. However, another report should be mentioned because of its historical interest and the lessons it may teach.
In 1900 to 1905, in the Bitter Root Valley, a tick-borne disease emerged, which became known as Rocky Mountain spotted fever. Although Ricketts et al. later published a report (2), which identified the causative agent, in 1904 L.B. Chowning and W.M. Wilson published Studies on Pyroplasma hominis (3). They reported finding Pyroplasma (since changed to Babesia) in the blood of approximately 20 patients with spotted fever. They studied this organism in detail and even found the reservoir for it in the local rodent species. Wilson et al. thought that the organism was the causative agent of spotted fever. On the basis of their excellent plates and descriptions, it is clear that the organism they were describing was what we later came to know as Babesia microti.
The work of Wilson and Chowning was ignored and forgotten for many years. They had incorrectly concluded that spotted fever was caused by a parasite. For many years it was "well known" that Babesia infections became apparent in human patients only on removal or inactivation of the spleen. That persons with functional spleens were subject to infection with B. microti was finally established by the so-called Nantucket outbreak (4) and subsequent publications.
Therefore, Wilson and Chowning's work reports several cases of simultaneous infections of humans by two tickborne pathogens; i.e., patients had spotted fever and B. microti in the blood. More poignant was that an "emerging" disease of humans was missed and not discovered again for some 70 years.
- Sexton DJ, Corey GR, Carpenter C, Kong LQ, Gandhi T, Breitschwerdt E, Dual infection with Ehrlichia chaffeensis and a spotted fever group rickettsia: a case report. Emerg Infect Dis. 1998;4:311–6.
- Ricketts HT. Some aspects of Rocky Mountain spotted fever. Rev Infect Dis. 1909;:1227–40.
- Wilson LB, Chowning WM. Studies on Pyroplasma hominis. Rev Infect Dis. 1904;1:31–57.
- Ruebush TK, Juranek DD, Chisholm ES, Snow PC, Healy GR, Sulzer AJ. Human babesiosis on Nantucket Island. N Engl J Med. 1977;297:825–87.