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Hemogregarine and Rickettsial infection in ticks of toads from northeastern Colombia.

ABSTRACT: The toads Rhinella spp. are in constant contact with humans and domestic animals and are commonly parasitized by ticks, which are also potential vectors of pathogenic microorganisms, such as apicomplexans and rickettsia. However, little is known about microorganisms associated with toad ticks. In this work, we molecularly evaluated the presence of Rickettsia spp. and hemogregarines in ticks of Rhinella horribilis and R. humboldti in the Colombian Caribbean, finding two different species of Rickettsia: the colombianensi strain and one close to R. bellii. In the case of hemogregarines, since only 18S gene sequences are available, it is difficult to define species and place them correctly in a phylogeny, but most of our samples show a 99% identity with Hemolivia stellata, while others identical to each other seem to form another clade within this genre. All collected ticks were identified as Amblyomma dissimile, representing the first time that H. stellata was recorded in this tick. The prevalence of both microorganisms was very high, which makes it necessary to generate robust phylogenies to clarify their taxonomic diversity and to correctly define their ecological role and pathogenicity, which should be taken into account in amphibian conservation plans and veterinary medicine.

SUBMITTER: Cotes-Perdomo A

PROVIDER: S-EPMC6032028 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundBrazilian spotted fever (BSF), caused by the bacterium Rickettsia rickettsii, is the deadliest spotted fever of the world. In most of the BSF-endemic areas, capybaras (Hydrochoerus hydrochaeris) are the principal host for the tick Amblyomma cajennense, which is the main vector of BSF.MethodsIn 2012, a BSF case was confirmed in a child that was bitten by ticks in a residential park area inhabited by A. cajennense-infested capybaras in Itú municipality, southeastern Brazil. Host questing A. cajennense adult ticks were collected in the residential park and brought alive to the laboratory, where they were macerated and intraperitoneally inoculated into guinea pigs. A tick-inoculated guinea pig that presented high fever was euthanized and its internal organs were macerated and inoculated into additional guinea pigs (guinea pig passage). Tissue samples from guinea pig passages were also used to inoculate Vero cells through the shell vial technique. Infected cells were used for molecular characterization of the rickettsial isolate through PCR and DNA sequencing of fragments of three rickettsial genes (gltA, ompA, and ompB). Blood serum samples were collected from 172 capybaras that inhabited the residential park. Sera were tested through the immunofluorescence assay using R. rickettsii antigen.ResultsA tick-inoculated guinea pig presented high fever accompanied by scrotal reactions (edema and marked redness). These signs were reproduced by consecutive guinea pig passages. Rickettsia was successfully isolated in Vero cells that were inoculated with brain homogenate derived from a 3rd passage-febrile guinea pig. Molecular characterization of this rickettsial isolate (designated as strain ITU) yielded DNA sequences that were all 100% identical to corresponding sequences of R. rickettsii in Genbank. A total of 83 (48.3%) out of 172 capybaras were seroreactive to R. rickettsii, with endpoint titers ranging from 64 to 8192.ConclusionsA viable isolate of R. rickettsii was obtained from the tick A. cajennense, comprising the first viable R. rickettsi isolate from this tick species during the last 60 years. Nearly half of the capybara population of the residential park was seroreactive to R. rickettsii, corroborating the findings that the local A. cajennense population was infected by R. rickettsii.

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Hemogregarine and Rickettsial infection in ticks of toads from northeastern Colombia.

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