A 6-year-old, male Labrador retriever was examined in June 2011 for decreased activity and reluctance to climb stairs. The dog had a fever and stiff gait; history revealed that 2 ticks had been attached to the dog 2 months previously. Assay was positive for Anaplasma-specific antibodies. Doxycycline was dispensed for 21 days and carprofen as needed for pain; amoxicillin and Fortiflora were added 5 days later. The dog returned to normal in July.

In August, the dog presented for decreased appetite, lethargy, and recurrent vomiting. Fever and thrombocytopenia were noted; Anaplasma-species antibodies were detected on in-house test. Doxycycline was dispensed and PCR testing for Anaplasma and Ehrlichia spp initiated. Sequencing revealed 100% DNA similarity to E muris. Doxycycline was discontinued when the dog experienced vomiting and diarrhea; clostridial enteritis was diagnosed. Amoxicillin, metronidazole, and metoclopramide were dispensed. The dog improved but returned later for decreased activity and hematuria. A 10-day course of cephalexin was recommended for presumptive urinary tract infection; however, hematuria persisted and platelet count decreased. Doxycycline was reinstituted, and hematuria resolved; no additional medical problems were noted. Blood taken 1 month later showed seroreactivity to Anaplasma spp peptide. Results from IFA testing for other organisms and PCR testing for Ehrlichia spp, including E muris, were negative. The dog may have been coinfected with A phagocytophilum and E muris at initial presentation, although it is possible E muris transmission occurred later (before the second fever).

E muris was first identified in mice in Japan in the mid-1990s. In 2011, archived adult Ixodes ticks collected in northern Wisconsin were analyzed by PCR testing; ~1% contained E muris DNA. There have been confirmed human cases in Minnesota and Wisconsin; symptoms in human patients are similar to those caused by E canis, E chaffeensis, and E ewingii. This may be the first dog identified with E muris. Several other Ehrlichia spp are being investigated for causing disease in humans, and we can expect that some will also cause disease in companion animals.—Patricia Thomblison, DVM, MS

Ehrlichia muris in a dog from Minnesota. Hegarty BC, Maggi RG, Koskinen P, et al. JVIM 26:1217-1220, 2012.

This capsule is a part of the One Health Initiative.