Cross-sectional study of the seroprevalence to Borrelia burgdorferi sensu lato and granulocytic Ehrlichia spp. and demographic, clinical and tick-exposure factors in Swedish horses

A cross-sectional study of the seroprevalence to Borrelia burgdorferi sensu tate and granulocytic Ehrlichia spp. in Swedish horses was conducted to ev aluate associations with demographic, clinical and tick-exposure factors. F rom September 1997-1998, blood samples from 2018 horses were collected from the animals presented to veterinary clinics affiliated with the Swedish Ho rserace Totalizator Board (regardless of the primary cause for consultation ). Standardized questionnaires with information both from owners and attend ing veterinarians accompanied each blood sample. The apparent seroprevalenc es to B. burgdorferi s, l. and granulocytic Ehrlichia spp, were 16.8 and 16 .7%, respectively. The northern region had the lowest seroprevalences. Four logistic models were developed (controlling for demographic variables). In the disease model of seropositivity to B. burgdorferi s. l,, age, breed, g eographic region, the serologic titer to granulocytic Ehrlichia spp., seaso n and the diagnosis coffin-joint arthritis were significant. In the tick-ex posure model of B. burgdorferi S. l,, pasture access the previous year and gender were significant. Age, racing activity, geographic region, season an d the serologic titer to B. burgdorferi s. l, were associated with positivi ty to granulocytic Ehrlichia spp. In the tick-exposure model of granulocyti c Ehrlichia spp., pasture access was a risk factor, An interaction between racing activity and geographic region showed that the risk of positive sero logic reactions to Ehrlichia spp, was increased in the horse population in the south and middle of Sweden, but only among horses not used for racing. Except for the positive association between coffin-joint arthritis and sero logic reactions to B. burgdorferi s. l., there were no significant associat ions in the multivariable models between non-specific or specific clinical sign or disease with seropositivity to either of these agents. (C) 2001 Els evier Science B.V. All rights reserved.