Abstract
This study compared the vector competence of four populations of Rhipicephalus sanguineus group ticks for the bacterium Ehrlichia canis, the agent of canine monocytic ehrlichiosis (CME). Ticks (larvae and nymphs) from the four populations—one from São Paulo state, southeastern Brazil (BSP), one from Rio Grande do Sul state, southern Brazil (BRS), one from Argentina (ARG), and one from Uruguay (URU)–were exposed to E. canis infection by feeding on dogs that were experimentally infected with E. canis. Engorged ticks (larvae and nymphs) were allowed to molt to nymphs and adults, respectively, which were tested by molecular analysis (E. canis-specific PCR assay) and used to infest naïve dogs. Through infestation of adult ticks on naïve dogs, after nymphal acquisition feeding on E. canis-infected dogs, only the BSP population was shown to be competent vectors of E. canis, i.e., only the dogs infested with BSP adult ticks developed clinical illness, seroconverted to E. canis, and yielded E. canis DNA by PCR. This result, demonstrated by two independent replications, is congruent with epidemiological data, since BSP ticks were derived from São Paulo state, Brazil, where CME is highly endemic. On the other hand, BRS, ARG, and URU ticks were derived from a geographical region (South America southern cone) where CME has never been properly documented. Molecular analysis of unfed adults at 30 days post molting support these transmission results, since none of the BRS, ARG, and URU ticks were PCR positive, whereas 1% of the BSP nymphs and 31.8% of the BSP adults contained E. canis DNA. We conclude that the absence or scarcity of cases of CME due to E. canis in the South America southern cone is a result of vector incompetence of the R. sanguineus group ticks that prevail on dogs in this part of South America.
Highlights
The Rhipicephalus sanguineus complex is a group of at least 12 morphologically closely related species, including Rhipicephalus sanguineus sensu stricto (s.s.) [1]
All animals (Dogs 1, 8, 15) that were intravenously inoculated with E. canis-infected blood developed signs of canine monocytic ehrlichiosis (CME), which started at the 14th days after inoculation (DAI) and lasted until at least the 22th DAI, when doxycycline therapy (10 mg/Kg, 12/12 h P.O., for 28 days) was initiated in order to prevent clinical complications
We evaluated the vector competence of four geographic distinct populations of R. sanguineus group for the canine pathogen E. canis
Summary
The Rhipicephalus sanguineus complex is a group of at least 12 morphologically closely related species, including Rhipicephalus sanguineus sensu stricto (s.s.) [1]. Moraes-Filho et al [6] assigned these two species as ‘temperate’ and ‘tropical’, the former restricted to the southern cone of South America (Uruguay, Argentina, Chile, and the southernmost state of Brazil), and the later encompassing the rest of Latin America, from Mexico to Brazil This distribution, based on genetic analysis, was corroborated by subsequent data [7]. To the current situation of Latin America, recent genetic studies showed that the taxon R. sanguineus s.s. was applied to distinct genospecies on other continents [6,9,10,11], corroborated by biological analysis [9] In view of this unequivocally taxonomic problem, Nava et al [1] recommended that, currently, it is not possible to assign the specific name R. sanguineus s.s. to any tick population of the world.
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