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

Abstract

Background: Rhipicephalus 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.

Results: Initially, 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.

Conclusions: The 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.

Figure 1

Effect of A. platys and/or E. canis infections on hematocrits of dogs prior to doxycycline treatment. (a.) Uninfected controls are compared to single infections of A. platys (Group A), E. canis (Group E) or simultaneous infections of both A. platys and E. canis (Group A+E). (b.) Groups receiving sequential infections of A. platys followed by E. canis (Group A→E) and E. canis followed by A. platys (Group E→A), with the challenge infection at 112 days PI (dotted line). Controls shown in panel A. (Hematocrit shown as mean ± SEM per group.)

Figure 2

Effect of A. platys and/or E. canis infections on platelet counts of dogs prior to doxycycline treatment. (a.) Uninfected controls are compared to single infections of A. platys (Group A), E. canis (Group E) or simultaneous infections of both A. platys and E. canis (Group A+E). (b.) Uninfected controls are compared to groups receiving sequential infections of A. platys followed by E. canis (Group A→E) and E. canis followed by A. platys (Group E→A), with the challenge infection at 112 days PI (dotted line). (Platelet counts shown as mean ± SEM per group).

Figure 3

SNAP 4Dx OD values for Anaplasma spp. vary with E. canis co-infection and doxycycline treatment. (a.) Comparison of only A. platys infected (Group A) to A. platys infected challenged with E. canis on day 112 PI (Group A→E). Three dogs from each group were either treated with doxycycline starting at day 211 (+doxy) or not treated. (b.) Comparison of Anaplasma spp. OD values for co-infected dogs (Group A+E). Three dogs from this group were treated with doxycycline at day 211 PI (+doxy) and three dogs were left untreated. (Mean OD per group).

Figure 4

SNAP 4Dx OD values for E. canis remain elevated through day 420 of the study. Comparison of mean OD values for dogs infected only with E. canis (Group E), infected with A. platys and challenged with E. canis or infected with E. canis and challenged with A. platys (Groups A→E and E→A) at day 112, and dogs co-infected with A. platys and E. canis (Group A+E). Three of six dogs in each group were treated with doxycycline beginning at day 211 (+doxy) while the other three dogs per group served as untreated controls (not shown). (Mean OD per group.)

Figure 5

Differences in platelet counts in dogs infected with A. platys and/or E. canis and receiving doxycycline treatment (a.) relative to their untreated controls (b). Three dogs from each group were either treated with doxycycline starting at day 211 (+doxy) or not treated. All doxycycline treated and untreated dogs were administered dexamethasone between days 410 and 414 PI. (Platelet counts shown as mean ± SEM per group.)