Six patients from northern Minnesota and Wisconsin with a febrile illness accompanied by granulocytic cytoplasmic morulae suggestive of ehrlichial infection were identified. Two patients died, and splenic granulocytes of one patient contained cytoplasmic vacuoles with organisms ultrastructurally characteristic of ehrlichiae. From one patient, a 1.5-kb DNA product was amplified by PCR with universal eubacterial primers of 16S rDNA. Analysis of the nucleotide sequence of the amplified product revealed 99.9 and 99.8% similarities with E. phagocytophila and E. equi, respectively, neither of which has previously been known to infect humans. From the variable regions of the determined sequence, a forward primer specific for three organisms (human granulocytic ehrlichia, E. phagocytophila, and E. equi) and a reverse primer for these ehrlichiae and E. platys were designed. By nested PCR with amplification by the universal primers and then reamplification with the specific primers described above, the expected 919-bp product was generated from the blood of the index patient and three additional patients. Blood from these four patients and two more patients with granulocytic morulae contained DNA which was amplified by nested PCR involving a combination of a universal primer and the human granulocytic ehrlichia-E. phagocytophila-E. equi-E. platys group-specific primer. This apparently vector-borne human granulocytic ehrlichia has only 92.5% 16S rDNA homology with E. chaffeensis. Nested PCR with group-specific primers did not amplify E. chaffeensis DNA, and E. chalfeensis-specific primers did not amplify DNAs of the human granulocytic ehrlichia. Thus, six patients were shown to be infected by an Ehrlichia species never previously reported to infect humans.

Seventeen Minnesota and Wisconsin dogs with granulocytic ehrlichosis were studied. The diagnoses were made by finding ehrlichia morulae in peripheral blood neutrophils. Eight dogs were studied retrospectively, and nine dogs were studied prospectively. The medical records of all dogs were reviewed. Eighty-eight percent of the dogs were purebred and 76% were spayed females. The median age was 8 years. Sixty-five percent of the cases were diagnosed in October and November. Fever and lethargy were the most common clinical signs. The most frequent laboratory findings were lymphopenia, thrombocytopenia, elevated activities of serum alkaline phosphatase and amylase, and hypoalbuminemia. No dogs seroreacted to Ehrlichia canis or Ehrlichia chaffeensis antigens, which are cross-reactive. Seventy-five percent of the dogs tested during the acute phase of disease and 100% of the dogs tested during convalescence were seropositive for E. equi antigens. Granulocytic ehrlichial 16S rRNA gene DNAs from six dogs were amplified by PCR. Sequence analysis of a 919-bp sequence of the ehrlichial 16S rRNA gene amplified by PCR from the blood of two dogs revealed the agent to be identical to the agent of human granulocytic ehrlichiosis in Minnesota and Wisconsin and to be very similar to E. equi and Ehrlichia phagocytophila and less similar to E. canis, Ehrlichia ewingii, and E. chaffeensis. The geographic, clinical, serologic, and molecular evidence indicates that granulocytic ehrlichiosis in Minnesota and Wisconsin dogs is not caused by E. ewingii, but suggests that it is a zoonotic disease caused by an agent closely related to E. equi and that dogs likely contribute to the enzootic cycle and human infection.

Ehrlichia equi, a rickettsia described from horses in California 30 yr ago, causes equine granulocytic ehrlichiosis throughout the Americas and possibly Europe. Here, we report experimental transmission of E. equi from infected to susceptible horses through bites of western blacklegged ticks, Ixodes pacificus (Cooley & Kohls). In preliminary field studies, only I. pacificus consistently infested horses and vegetation at 3 locations with contemporary cases of equine ehrlichosis, and in particular, I. pacificus was the only species found attached to all of the infected horses. Exposure to bites of ticks in the genus Ixodes poses previously unrecognized and serious health risks to humans and animals.

No abstract

No abstract