BackgroundDogs that have clinical leishmaniosis (ClinL), caused by the parasite Leishmania infantum, are commonly co-infected with other pathogens, especially vector-borne pathogens (VBP). A recent PCR-based study found that ClinL dogs are more likely to be additionally infected with the rickettsial bacteria Ehrlichia canis. Further information on co-infections in ClinL cases with VBP, as assessed by serology, is required. The research described in this report determined if dogs with ClinL are at higher risk of exposure to VBP than healthy control dogs using a case-control serology study.ResultsOf the 47 dogs with ClinL, anti-E. canis/ Ehrlichia ewingii antibodies were detected in 17 (36.2%), anti-Anaplasma phagocytophilum/Anaplasma platys antibodies in 5 (10.6%) and antigen for Dirofilaria immitis in 2 (4.3%). Of the 87 control dogs, anti-E. canis/E. ewingii antibodies were detected in 14 (16.1%) and anti-A. phagocytophilum/A. platys antibodies in 2 (2.3%). No anti-Borrelia burgdorferi antibody tests were positive. No statistical differences between the ClinL dogs and control dogs regarding lifestyle or use of ectoparasitic prevention, were identified. The ClinL was significantly associated with anti-E. canis/E. ewingii antibodies (odds ratio = 2.9, 95% confidence interval: 1.3–6.7, P = 0.010) compared to controls by both multivariable logistic regression and structural equation modelling.ConclusionsIt was demonstrated that an increased risk for E. canis/E. ewingii seropositivity is present in dogs with ClinL compared to clinically healthy control dogs, despite similar ectoparasitic prevention use and lifestyle. Based on these findings it is suggested that dogs with ClinL should not only be tested for E. canis co-infection using PCR but also serologically for E. canis/E. ewingii.