Molecular and Antigenic Comparison of Ehrlichia canis Isolates from Dogs, Ticks, and a Human in Venezuela

Abstract

We previously culture isolated a strain of Ehrlichia canis, the causative agent of canine ehrlichiosis, from a human in Venezuela. In the present study, we examined whether dogs and ticks are infected with E. canis in Venezuela and, if so, whether this is the same strain as the human isolate. PCR analysis using E. canis-specific primers revealed that 17 of the 55 dog blood samples (31%) and all three pools of four Rhipicephalus sanguineus ticks each were positive. An ehrlichial agent (Venezuelan dog Ehrlichia [VDE]) was isolated and propagated in cell culture from one dog sample and was further analyzed to determine its molecular and antigenic characteristics. The 16S rRNA 1,408-bp sequence of the new VDE isolate was identical to that of the previously reported Venezuelan human Ehrlichia isolate (VHE) and was closely related (99.9%) to that of E. canis Oklahoma. The 5 (333-bp) and 3 (653-bp) sequences of the variable regions of the 16S rRNA genes from six additional E. canis-positive dog blood specimens and from three pooled-tick specimens were also identical to those of VHE. Western blot analysis of serum samples from three dogs infected with VDE by using several ehrlichial antigens revealed that the antigenic profile of the VDE was similar to the profiles of VHE and E. canis Oklahoma. Identical 16S rRNA gene sequences among ehrlichial organisms from dogs, ticks, and a human in the same geographic region in Venezuela and similar antigenic profiles between the dog and human isolates suggest that dogs serve as a reservoir of human E. canis infection and that R. sanguineus, which occasionally bites humans residing or traveling in this region, serves as a vector. This is the first report of culture isolation and antigenic characterization of an ehrlichial agent from a dog in South America, as well as the first molecular characterization of E. canis directly from naturally infected ticks.

Prevalence of ehrlichial infection among dogs and ticks in Northeastern Brazil

“…There are scarce data available regarding E. canis infection in R. sanguineus (MURPHY et al, 1998;UNVER et al, 2001;NDIP et al, 2007). In the study performed by Aguiar et al (2007b) in Monte Negro (State of Rondônia) and São Paulo (State of São Paulo), E. canis-infection rates in R. sanguineus ticks varied from 2.4 (4/165) to 6.2% (10/162).…”

“…A new subspecies of Ehrlichia canis, recently characterized in Venezuela, underscored the zoonotic potential of this genre, in view of identifying persistent and asymptomatic infection in a human patient with involvement of a dog and also ticks infected by the same microorganism (PEREZ; RIKIHISA; WEN, 1996;PEREZ et al, 2006;UNVER et al, 2001). DNA of E. chaffeensis has also been detected in members of the Cervidae family (Blastocerus dichotomus) captured in the area of the Paraná River in southeastern São Paulo and eastern Mato Grosso do Sul, Brazil (MACHADO et al, 2006).…”

HEMATOLOGICAL PARAMETERS AND SEROPREVALENCE OF Ehrlichia canis AND Babesia vogeli IN DOGS

“…Canine monocytic ehrlichiosis (CME) is a major infectious disease that affects dogs and is also of interest in public health due to the recent discoveries of infection by E. canis in humans in Venezuela, where the agent was likely transmitted by the tick vector R. sanguineus (48,49) . Thus, taking into consideration the concern about the zoonotic potential of E. canis and other hemoparasites, further studies on the parasitism of humans by the R. sanguineus are necessary.…”

Molecular and serological detection of tick-borne pathogens in dogs from an area endemic for Leishmania infantumin Mato Grosso do Sul, Brazil

“…Antibodies to E. canis have also been detected in almost all Brazilian states, with the prevalence of exposure in dogs ranging from 4.8% (SAITO et al, 2008) to 73% (NAKAGHI et al, 2008). Although E. canis DNA has been detected in humans in Venezuela (PEREZ et al, 2006;UNVER et al, 2001), the importance of the parasite as a zoonotic agent remains unknown.…”