Letters: Ehrlichia canis infection and epistaxis
In the article "Coinfection with multiple tick-borne pathogens" published in the March 2006 Veterinary Medicine parasitology supplement, Drs. Adam Mordecai, Erick Spencer, and Rance Sellon state that epistaxis has not been observed in dogs with experimental Ehrlichia canis infection. The authors suggest that, in fact, the epistaxis seen during E. canis infection is caused by coinfection with a Bartonella species. Actually, epistaxis is a feature of laboratory infection in German shepherds during the chronic phase of the disease when there is severe thrombocytopenia. This was confirmed in a study conducted in the 1970s.1
William Buhles, DVM, PhD
REFERENCE1. Buhles WC, Huxsoll DL, Ristic M. Tropical canine pancytopenia: clinical, hematologic, and serologic response of dogs to Ehrlichia canis infection, tetracycline therapy, and challenge inoculation. J Infect Dis 1974;130:357-367.
Dr. Mordecai responds: We thank Dr. Buhles for pointing out his study that documented epistaxis in thrombocytopenic German shepherds experimentally infected with Ehrlichia canis and apologize for the oversight. We should have stated that epistaxis attributable solely to experimental E. canis infection in dogs has not been well-documented. This is in keeping with the theme of the introductory paragraphs that clinical signs previously attributable to infection with a single tick-borne pathogen are being reassessed in light of increasing awareness of coinfection.
In the study done by Dr. Buhles and colleagues, the E. canis organisms used to experimentally infect dogs were obtained from the blood of a naturally infected dog and maintained through subsequent passages in na? laboratory beagles with inoculation of whole blood from infected dogs. While steps were taken in that study to demonstrate that the blood inocula obtained from infected dogs was free of Babesia and Hemobartonella (Mycoplasma) species, knowledge and methodologies available at the time of that study did not permit the investigators to determine that the blood was also free of other tick-transmitted pathogens, such as Bartonella species, which—as stated in our article—are being viewed with increasing suspicion as contributors to clinical signs previously attributed to single infection with more well-known pathogens.
In the article, we did not specifically state, and did not specifically suggest, that all dogs with epistaxis and documented E. canis infection are infected with other tick-borne pathogens, but rather that clinicians today should still consider that coinfections may contribute to clinical signs and that identification of a single tick-borne infection may signal the presence of others. We are grateful to Dr. Buhles for giving us the opportunity to clarify this point.
Adam Mordecai, DVM