Association between canine leishmaniosis and Ehrlichia canis co-infection: a prospective case-control study

Abstract

Background: In the Mediterranean basin, Leishmania infantum is a major cause of disease in dogs, which are frequently co-infected with other vector-borne pathogens (VBP). However, the associations between dogs with clinical leishmaniosis (ClinL) and VBP co-infections have not been studied. We assessed the risk of VBP infections in dogs with ClinL and healthy controls.

Methods: We conducted a prospective case-control study of dogs with ClinL (positive qPCR and ELISA antibody for L. infantum on peripheral blood) and clinically healthy, ideally breed-, sex- and age-matched, control dogs (negative qPCR and ELISA antibody for L. infantum on peripheral blood) from Paphos, Cyprus. We obtained demographic data and all dogs underwent PCR on EDTA-blood extracted DNA for haemoplasma species, Ehrlichia/Anaplasma spp., Babesia spp., and Hepatozoon spp., with DNA sequencing to identify infecting species. We used logistic regression analysis and structural equation modelling (SEM) to evaluate the risk of VBP infections between ClinL cases and controls.

Results: From the 50 enrolled dogs with ClinL, DNA was detected in 24 (48%) for Hepatozoon spp., 14 (28%) for Mycoplasma haemocanis, 6 (12%) for Ehrlichia canis and 2 (4%) for Anaplasma platys. In the 92 enrolled control dogs, DNA was detected in 41 (45%) for Hepatozoon spp., 18 (20%) for M. haemocanis, 1 (1%) for E. canis and 3 (3%) for A. platys. No Babesia spp. or "Candidatus Mycoplasma haematoparvum" DNA was detected in any dog. No statistical differences were found between the ClinL and controls regarding age, sex, breed, lifestyle and use of ectoparasitic prevention. A significant association between ClinL and E. canis infection (OR = 12.4, 95% CI: 1.5-106.0, P = 0.022) was found compared to controls by multivariate logistic regression. This association was confirmed using SEM, which further identified that younger dogs were more likely to be infected with each of Hepatozoon spp. and M. haemocanis, and dogs with Hepatozoon spp. were more likely to be co-infected with M. haemocanis.

Conclusions: Dogs with ClinL are at a higher risk of co-infection with E. canis than clinically healthy dogs. We recommend that dogs diagnosed with ClinL should be tested for E. canis co-infection using PCR.

Keywords: Anaplasma platys; Canine leishmaniosis; Co-infection; Cyprus; Ehrlichia canis; Hepatozoon spp.; Leishmania infantum; Mycoplasma haemocanis; Structural equation model; Vector-borne pathogen.

Fig. 1

Comparison of VBPs detected by PCR and sequencing between dogs with ClinL (n = 50) and healthy control (n = 92). Abbreviations: VBP, vector-borne pathogen; ClinL, clinical leishmaniosis; A. platys, Anaplasma platys; E. canis, Ehrlichia cani; M. haemocanis, Mycoplasma haemocanis

Fig. 2

Structural equation model showing predictors of vector-borne co-infection (except Leishmania infantum), and pathogen covariance (including L. infantum). Values represent standardised coefficients among variables. Single headed arrows represent directional/causal relationships and double headed arrows covariance relationships among pathogens. For image clarity the coefficients of host characteristics predicting pathogens are listed next to each host characteristic. In all cases, except age, variables are binomial (0 or 1) with 1 equal to male, outside, ectoparasitic prevention use, pedigree and positive pathogen status. Significant relationships (P ≤ 0.05) denoted by bold font and trending relationships (P < 0.1) denoted by *. Abbreviations: A. platys, Anaplasma platys; E. canis, Ehrlichia canis; M. haemocanis, Mycoplasma haemocanis. Note: Values represent standardised coefficients among variables. Single headed arrows represent directional/causal relationships and double headed arrows covariance relationships among pathogens. For image clarity the coefficients of host characteristics predicting pathogens are listed next to each host characteristic. In all cases, except age, variables are binomial (0 or 1) with 1 equal to male, outside, ectoparasitic prevention use, pedigree and positive pathogen status. Significant relationships (P ≤ 0.05) denoted by bold font and trending relationships (P < 0.1) denoted by *.