Human granulocytic ehrlichiosis agent infection in a pony vaccinated with a Borrelia burgdorferi recombinant OspA vaccine and challenged by exposure to naturally infected ticks

A pony was vaccinated with recombinant OspA vaccine (rOspA) and then expose d 3 months later to Borrelia burgdorferi-infected ticks (Ixodes scapularis) collected in Westchester County, N.Y. At 2 weeks after tick exposure, the pony developed a high fever (105 degrees F), Buffy coat smears showed that 20% of neutrophils contained ehrlichial inclusion bodies (morulae). Flunixi n Meglumine (1 g daily) was given for 2 days, and the body temperature retu rned to normal. PCR for ehrlichial DNA was performed an blood samples for 1 0 consecutive days beginning when the pony was first febrile. This pony was monitored for another 3.5 months but developed no further clinical signs. The 44-kDa immunodominant human granulocytic ehrlichiosis antigen gene was amplified by PCR and cloned into a pCR2.1 vector. DNA sequence analysis of this gene showed it was only 8 bp different (99% identity) from the results reported by others (J.W. Ijdo et al., Infect. Immun. 66:3264-3269, 1998), Western blot analysis, growth inhibition assays, and repeated attempts to i solate B. burgdorferi all demonstrated the pony was protected against B. bu rgdorferi infection. These results highlight the potential for ticks to har bor and transmit several pathogens simultaneously, which further complicate s the diagnosis and vaccination of these emerging tick-borne diseases.