Experimental infection and co-infection of dogs with Anaplasma platys and Ehrlichia canis: hematologic, serologic and molecular findings

Sd Gaunt,Eb Breitschwerdt,Ppvp Diniz,L Lorentzen,Mj Beall,R Chandrashekar,Ba Stillman

doi:10.1186/1756-3305-3-33

Abstract

BackgroundRhipicephalus sanguineus is a ubiquitous tick responsible for transmitting Ehrlichia canis and most likely Anaplasma platys to dogs, as either single or co-infections. The objective of this study was to assess the effects of either simultaneous or sequential experimental infections with E. canis and A. platys on hematological and serological parameters, duration of infection, and efficacy of doxycycline therapy in dogs infected with one or both organisms. Six dogs per group were either uninfected, A. platys infected, E. canis infected, A. platys and E. canis co-infected, A. platys infected and E. canis challenged or E. canis infected and A. platys challenged at day 112 post-infection (PI). Doxycycline treatment was initiated at 211 days PI, followed by dexamethasone immunosuppression beginning 410 days PI.ResultsInitially, transient decreases in hematocrit occurred in all groups infected with E. canis, but the mean hematocrit was significantly lower in the A. platys and E. canis co-infected group. All dogs except the controls developed marked thrombocytopenia after initial infection followed by gradually increased platelet counts by 112 days PI in groups with the single infections, while platelet counts remained significantly lower in the A. platys and E. canis co-infected group. Both sequential and simultaneous infections of A. platys and E. canis produced an enhanced humoral immune response to A. platys when compared to infection with A. platys alone. Likewise, co-infection with E. canis and A. platys resulted in a more persistent A. platys infection compared to dogs infected with A. platys only, but nearly all A. platys infected dogs became A. platys PCR negative prior to doxycycline treatment. E. canis infected dogs, whether single or co-infected, remained thrombocytopenic and E. canis PCR positive in blood for 420 days. When treated with doxycycline, all E. canis infected dogs became E. canis PCR negative and the thrombocytopenia resolved. Despite immunosuppression, neither A. platys nor E. canis DNA was PCR amplified from doxycycline-treated dogs.ConclusionsThe results of this study demonstrate that simultaneous or sequential infection with A. platys and E. canis can alter various pathophysiological parameters in experimentally infected dogs, and because natural exposure to multiple tick-borne pathogens occurs frequently in dogs, awareness of co-infection is important in clinical practice.

Highlights

Rhipicephalus sanguineus is a ubiquitous tick responsible for transmitting Ehrlichia canis and most likely Anaplasma platys to dogs, as either single or co-infections
Hematology and clinical signs Compared to the non-infected controls, dogs infected with E. canis (Group E) developed decreased hematocrits, while the hematocrits of dogs infected with A. platys (Group A) did not differ from controls (Fig. 1a)
At several time points, their hematocrits were significantly lower than dogs infected with E. canis alone (One-way ANOVA, p ≤ 0.05)

Summary

Introduction

Rhipicephalus sanguineus is a ubiquitous tick responsible for transmitting Ehrlichia canis and most likely Anaplasma platys to dogs, as either single or co-infections. A. platys infections are often found in the same geographic regions as E. canis and evidence of exposure to or infection with both organisms is often detected in the same dog [5,6,7,8]. Both organisms are found on all continents throughout the world, but are more prevalent in tropical and subtropical climates [2,9]. A. platys infections cause a cyclic thrombocytopenia that may be severe enough to result in bleeding, including petechiae and ecchymoses, but most dogs are thought to control the infection immunologically [1]

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