Artificial Feeding of Ornithodoros fonsecai and O. brasiliensis (Acari: Argasidae) and Investigation of the Transstadial Perpetuation of Anaplasma marginale

Anaplasma marginale is a Gram-negative, obligate intraerythrocytic bacterium that causes bovine anaplasmosis. While hard ticks of the genera Dermacentor and Rhipicephalus can be biological vectors, transmitting this pathogen via saliva during blood meals, blood-sucking insects, and fomites play a role as mechanical vectors. Little is known about the interaction between Anaplasma marginale and Argasidae ticks. Among soft ticks, Ornithodoros fonsecai (Labruna and Venzal) and Ornithodoros brasiliensis Aragão inhabit environments surrounding localities where many cases of bovine anaplasmosis have been reported. Ticks of the species O. fonsecai parasitize bats, while O. brasiliensis can parasitize different vertebrate species. Therefore, the present study aimed to feed third-instar nymphs artificially (N3) of O. fonsecai and O. brasiliensis using blood samples obtained from a calf naturally infected with A. marginale and rabbit blood added to A. marginale-containing bovine erythrocytes, to investigate the ability of these nymphs to acquire, infect and transstadially perpetuate this agent. For the artificial feeding system, adapted chambers and parafilm membranes were used. Nymphs of both tick species were submitted to different replications weighed before and after each feeding. Blood samples and molted ticks were submitted to DNA extraction, quantitative real-time PCR for the msp1β gene to detect A. marginale DNA, while a semi-nested polymerase chain reaction for the msp1α gene was performed for genotyping. Using calf blood naturally infected with A. marginale, among the three artificial feeding replications performed with O. fonsecai and O. brasiliensis nymphs, the DNA of A. marginale was detected in both nymphs after 30-50 days of molting. For artificial feeding with rabbit blood added to bovine erythrocytes containing A. marginale, the DNA of this pathogen was also detected in both nymph species. As for the assay for the msp1α gene, strains were found Is9; 78 24-2; 25; 23; α; and β. It was concluded that nymphs (N3) of O. fonsecai and O. brasiliensis could feed artificially through a parafilm membrane using blood from calves and rabbits infected by A. marginale. The DNA of A. marginale was detected in nymphs fed artificially of both tick species studied after molt. However, further studies are needed to confirm transstadial perpetuation in other instars and their host transmission capacity.

Analysis on the prokaryotic microbiome in females and embryonic cell cultures of Rhipicephalus sanguineus tropical and temperate lineages from two specific localities in Brazil

Two lineages of Rhipicephalus sanguineus are known in Brazil: the temperate or southern and the tropical or northern populations. The distribution patterns of both lineages of R. sanguineus have epidemiological implications that can affect vectorial competence concerning Ehrlichia canis, the agent of canine monocytic ehrlichiosis. Intending to identify the microbiomes of both lineages and compare microorganisms in R. sanguineus, we used the 16S rRNA (V4-V5 region) gene-based metataxonomic approach, through NGS sequencing on the MiSeq Illumina platform. We selected specimens of females from the environment and samples of primary embryonic cell cultures, from both lineages, and this was the first study to investigate the prokaryotic microbiome in tick cell cultures. The results showed that many bacterial taxa detected in the samples were typical members of the host environment. A significant diversity of microorganisms in R. sanguineus females and in embryonic cell cultures from both lineages was found, with emphasis on the presence of Coxiella in all samples, albeit in different proportions. The Coxiella species present in the two lineages of ticks may be different and may have co-evolved with them, thus driving different patterns of interactions between ticks and the pathogens that they can harbor or transmit to vertebrate hosts.

Establishment and characterization of a cell line (RBME-6) of Rhipicephalus (Boophilus) microplus from Brazil

Tick cell lines have already proved to be a useful tool for obtaining more information about possible vector species and the factors governing their ability to transmit a pathogen. Here, we established and characterized a cell line (RBME-6) derived from embryos of Rhipicephalus microplus from Brazil. Primary tick cell cultures were prepared in L-15B medium supplemented with 20% fetal bovine serum and 10% tryptose phosphate broth. The cell monolayers were subcultured when they reached a density of approximately 8 × 10 ⁵ cells/mL (95% viability). Only after the sixth subculture were cells thawed from storage in liquid nitrogen successfully. Cytological analyses were performed using live phase contrast microscopy and cytocentrifuge smears stained with Giemsa, while periodic acid-Schiff and bromophenol blue staining techniques were used to detect total polysaccharides and total protein, respectively . No DNA from Anaplasma spp., Anaplasma marginale, Babesia spp., Bartonella spp., Coxiella spp., Ehrlichia canis, Rickettsia spp. or Mycoplasma spp. was detected in the cells through PCR assays. In addition, we performed chromosomal characterization of the tick cell line and confirmed the R. microplus origin of the cell line through conventional PCR and sequencing of a fragment of the mitochondrial 16S rRNA gene. In conclusion, we established and characterized a new cell line from a Brazilian population of R. microplus, which may form a useful tool for studying several aspects of ticks and tick-borne pathogens.

Successful Infection of Tick Cell Cultures of Rhipicephalus sanguineus (Tropical Lineage) with Ehrlichia canis

There are two distinct lineages of ticks, Rhipicephalus sanguineus, in South America: tropical and temperate lineages. Only the tropical lineage is recognized as competent vector for Ehrlichia canis. The epidemiological data of canine monocytic ehrlichiosis is congruent with the distribution of the two lineages of R. sanguineus. Herein, we report the infection of R. sanguineus (tropical lineage) cell cultures with E. canis, after cryopreservation. R. sanguineus (tropical lineage) cell identity was confirmed by sequencing using a 16S rDNA gene fragment. Tick cell cultures were prepared in L-15B medium supplemented with 10%, 15%, and 20% Fetal Bovine Serum (FBS), and 10% of Tryptose Phosphate Broth (TPB). Cell cultures developed better at the concentration of 20% of FBS. Cultures in the fifth harvest (approximately 7 months later) were selected for the first infections. Optimal R. sanguineus cell growth and adhesion was observed (5.0 × 106 cells/mL, and the population doubling time every 57 h). Once infected with E. canis, the cultures were maintained in L-15B medium supplemented with 2% and 5% of FBS fortified with iron and 10% TPB. Infected cells were also cryopreserved. DNA was extracted from infected and noninfected cells and analyzed using quantitative real-time PCR targeting the E. canis-dsb gene. Primary culture of the fifth passage was infected by E. canis and it maintained the pathogen for at least 40 days before partial cell destruction. Subcultures of infected cells (fresh and cryopreserved cultures) onto new tick cell cultures were successful. The E. canis infection was confirmed by real-time PCR and light and transmission electron microscopy. The R. sanguineus (tropical lineage) cells infected with E. canis successfully infected new tick cell cultures, showing that these cells could be an alternative substrate for maintenance of this pathogen.