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Ticks are non-permanent ectoparasites with a worldwide distribution. With some exceptions, they are obligate hematophagous in both immature and adult stages that infest a great diversity of hosts including amphibians, reptiles, birds, and mammals 1. About 950 tick species have been recognized and are included in three families: Agasidae, Nuttalliellidae, and Ixodidae 2-4. Ticks are able to transmit bacteria (spirochetes and Rickettsiae), protozoans, viruses, and nematodes, making them one of the most important vectors of pathogenic agents in public and veterinary health 5. Hard ticks of the Ixodidae family are also the host species of Rickettsia spp. of unknown pathogenicity such as Rickettsia bellii6. This species has been detected in several species of Amblyomma and Ixodes genera 7-10.
Ixodes tropicalis Kohls, 1956, was described from females collected from the wild rodents Thomasomys nicefori (as Thomasomys aureus) in Valdivia (Antioquia), and from Dactylomys boliviensis in San Juan, Tambopata, Sandia (Puno, Perú) 11. Later, immature ticks determined as I. tropicalis were reported infesting another wild rodent, Nephelomys childi (as Oryzomys albigularis), in the Valle de Pichindé (Valle del Cauca), and the Pichindé virus was isolated from them 12. However, this report of I. tropicalis should be considered doubtful because its larvae and nymph have not been formally described 2. Thus, the only bona fide records of I. tropicalis correspond to those of the original description 11.
This study aims to report a case of I. tropicalis infesting a human, as well as the molecular detection of R. bellii in the south of the metropolitan area of Valle de Aburrá (Antioquia).
Materials and methods
On March 18, 2018, a 59-year-old man was gardening at his house in La Tablaza, La Estrella (Antioquia) (6°07'02”N, 75°38'14''W; 1756m). Later, he was found parasitized by a tick in the abdomen umbilical region, which was removed, placed in 96% ethanol, and sent to Universidad de Antioquia. The classification of the tick was made following the description of Kohls, 1956 11, with a stereomicroscope (Nikon SMZ1000™, Tokyo, Japan).
For molecular studies, the tick was longitudinally bisected using sterile scalpel blades and forceps, rinsed with distilled water to remove ethanol, and crushed with a homogenization pestle. The DNA was extracted using the commercial kit PureLink Genomic DNA Mini Kit™ (Invitrogen, Germany) following the manufacturer's instructions. DNA was tested by polymerase chain reaction (PCR) targeting the tick mitochondrial 16S rRNA gene 13 and gltA and ompA genes for Rickettsia spp., 16S rRNA gene of the family Anaplasmataceae, flagellin gene of Borrelia spp., and 18S rRNA gene of piroplasmid 14-18.
Results
The tick (a slightly engorged specimen) was identified as a female of I. tropicalis based on the following morphological characteristics: Idiosoma suboval, length from the tip of scapulae to the posterior margin of the body (excluding capitulum) 2.15 mm, width 1.66 mm; scutum, with numerous punctations, length 1.30 mm and width 1.15 mm; elevated lateral carinas extending from the scapulae to about the mild-length of the scutum; capitulum, porose areas large and semicircular in shape, separated by about the diameter of one, cornua short and rounded, palpal segment two a little longer than segment three, auricula large and posterolaterally directed; hypostome, broken at the base; coxa I of legs with moderately long internal spur and coxae I-IV with a conspicuous external spur; spiracular plate subcircular in shape (figure 1 A, B).
Photography by José Manuel Venzal
Figure 1 Female of Ixodes tropicalis. A. Dorsal view; capitulum, porose areas large, and semicircular in shape. B. Ventral view; hypostome, broken at the base, coxa I with moderately long internal spur, and spiracular plate subcircular in shape. The specimen has been deposited in the “Tick Collection of Instituto Nacional de Tecnología Agropecuaria, Estación Experimental Agropecuaria INTA Rafaela”: (INTA2470).
We amplified fragments of the mitochondrial 16S rRNA gene of the tick and gltA gene of Rickettsia and purified the amplicons using a PureLink Quick PCR Purification KitTM (Invitrogen, Germany), which we sent to Macrogen (Seoul, Korea) for sequencing. We did not amplify the DNA of piroplasmid, Borrelia spp., Anaplasmataceae agents, and the ompA gene of Rickettsia. The partial sequence obtained for the 16S rRNA gene of the specimen determined as I. tropicalis (ca. 410 bp) diverged by more than 5% when compared to the remaining Ixodes sequences available at the Genbank.
The partial gltA (784 bp) sequence showed 99.87% (783/784 bp) of identity with the corresponding R. bellii sequences (GenBank accession numbers: CP000087, AY375161, U59716). The sequences generated in the study were deposited in the GenBank under the accession numbers MT158325 for the 16S rRNA gene of I. tropicalis and MT174170 for the gltA gene of R. bellii.
Discussion
Besides I. tropicalis, another ten species belonging to the genus Ixodes are currently recognized in Colombia: Ixodes affinis in Carnivora and Artiodactyla 19,20; Ixodes auritulus in Passeriformes 21; Ixodes bocatorensis in Rodentia 22; Ixodes boliviensis in Didelphimorphia and Carnivora 20,23,24; Ixodes montoyanus in Artiodactyla 25,26; Ixodes lasallei in Rodentia 22,26,27; Ixodes luciae in Didelphimorphia 28; Ixodes pararicinus in Artiodactyla 19,29; Ixodes tapirus in Perissodactyla 11, and Ixodes venezuelensis in Rodentia 30. The records of Ixodes fuscipes31 and Ixodes brunneus23 for Colombia are currently considered not valid because the taxonomic status of the specimens assigned to these taxa is undetermined 32,33.
Most of these species do not infest humans. Only I. boliviensis, I. brunneus, and I. pararicinus were ocasionally found infesting humans 34. For Colombia, ten species of hard ticks have been reported parasitizing humans 34-37: Amblyomma dissimile, A. mixtum, A. oblongoguttatum, A. ovale, A. patinoi, A. sabanerae, Dermacentor imitans, D. nitens, Rhipicephalus microplus, and R. sanguineus sensu lato. Therefore, this finding corresponds to the first report of the genus Ixodes parasitizing humans in Colombia, as well as the first record for I. tropicalis in humans.
Regarding the detection of R. bellii in Colombia, Miranda, et al. (2014), detected it in the free-living larvae of Amblyomma sp. 38 from the northern coast of Colombia (Los Córdobas, Córdoba). In an area near Los Córdobas, R. bellii in A. ovale was detected and collected from a donkey in Necoclí 39. Besides, R. bellii has been detected in larvae of A. dissimile collected in Rhinella horribilis and Basiliscus basiliscus in the department of Magdalena 40,41.
As far as we know, this is the first report of I. tropicalis infesting a human and of R. bellii in this species in Colombia, and it would broaden the panorama regarding tick species infesting humans and the exposition to Rickettsial agents in the population living in the south of the metropolitan area of the Valle de Aburrá in Antioquia.
These findings demonstrate the presence of I. tropicalis as a potential parasite in humans in the south of the metropolitan area of the Valle de Aburrá Valley, as well as the report on the presence in this tick species of R. bellii, a bacteria of unknown pathogenicity in humans. Finally, it is crucial to determine other regions at risk of rickettsial agents' transmission besides those already known such as the Urabá area in Antioquia and the Villeta municipality in the department of Cundinamarca.
