Rickettsia amblyommatis infecting ticks and exposure of domestic dogs to Rickettsia spp. in an Amazon-Cerrado transition region of northeastern Brazil.
Authors: Costa Francisco B, da Costa Andréa P, Moraes-Filho Jonas, Martins Thiago F, Soares Herbert S, Ramirez Diego G, Dias Ricardo A, Labruna Marcelo B
Journal: PloS one
Summary
# Editorial Summary Researchers surveyed tick populations and Rickettsia exposure across 1,560 domestic dogs in northeastern Brazil's Amazon-Cerrado transition zone between 2011 and 2013, collecting ticks from 150 animals and serological samples from all participants to map rickettsial infection patterns. Molecular analysis identified Rickettsia amblyommatis predominantly in *Amblyomma cajennense* sensu stricto ticks (particularly in the Amazon biome), alongside 'Candidatus Rickettsia andeanae' in *A. parvum* and *Rickettsia bellii* in *A. ovale*; *Rhipicephalus sanguineus* s.l., the most abundant tick species overall at 68% of collections, tested negative for Rickettsia. Seropositivity to Rickettsia spp. reached 12.6% across the canine population, with R. amblyommatis accounting for 10.2%—notably higher antibody titres than other rickettsial antigens—and geographic variation was striking, ranging from 13.1–30.8% in Amazon localities where *A. cajennense* s.s. predominated, down to 1.9–6.5% in Cerrado areas further from the Amazon where *A. sculptum* dominated. Given the strong statistical association between rural exposure to Amblyomma ticks and rickettsial seropositivity, equine professionals working in similar transitional biome regions should consider R. amblyommatis as a relevant pathogen risk, particularly for horses grazing in or near Amazonian areas where *A. cajennense* s.s. populations are established, though further research is needed to characterise clinical significance in equine populations.
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Practical Takeaways
- •In Amazon-Cerrado transition regions of Brazil, rural dogs are at higher risk of R. amblyommatis exposure through A. cajennense s.s. ticks; monitor clinical signs in endemic areas
- •Tick species distribution varies by biome and correlates with Rickettsia exposure patterns—understanding local tick ecology helps predict disease risk
- •Dogs with outdoor/rural exposure to Amblyomma ticks warrant serological testing and tick control measures to reduce Rickettsia transmission risk
Key Findings
- •R. amblyommatis was identified in A. cajennense s.s. ticks with 12.6% canine seroreactivity to Rickettsia spp. overall and 10.2% specific to R. amblyommatis
- •Amazon biome localities showed highest canine seroreactivity rates (13.1-30.8%) where A. cajennense s.s. predominated, versus Cerrado localities with lowest rates (1.9-6.5%) where A. sculptum predominated
- •Rhipicephalus sanguineus s.l. was the most abundant tick species (68% of 959 ticks collected), followed by multiple Amblyomma species
- •Rural dogs with exposure to Amblyomma ticks showed statistically significant association with Rickettsia spp. seroreactivity