TICKCIDAL EFFECT OF MONOCLONAL ANTIBODIES AGAINST HEMOCYTES, OM21, IN AN ADULT FEMALE TICK, ORNITHODOROS MOUBATA (ACARI: ARGASIDAE)

Immunofluorescent detection in the ovary of host antibodies against a secretory ferritin injected into female Haemaphysalis longicornis ticks

Due to the continuous threat of ticks and tick-borne diseases to human and animal health worldwide, and the drawbacks of chemical acaricide application, many researchers are exploring vaccination as an alternative tick control method. Earlier studies have shown that host antibodies can circulate in the ticks, but it has not been confirmed whether these antibodies can be passed on to the eggs. We previously reported that ticks infesting rabbits immunized with a recombinant secretory ferritin of Haemaphysalis longicornis (HlFER2) had reduced egg production and hatching. Here we attempted to detect the presence of antibodies against HlFER2 in the ovary and eggs of female ticks through immunofluorescent visualization. Purified anti-HlFER2 antibodies or rabbit IgG for control was directly injected to engorged female H. longicornis. Ovaries and eggs after oviposition were collected and prepared for an indirect immunofluorescent antibody test. Positive fluorescence was detected in ovaries one day post-injection of anti-HlFER2 antibodies. Through silencing of Hlfer2 gene, we also determined whether the injected antibodies can specifically bind to native HlFER2. Immunofluorescence was observed in the oocytes of dsLuciferase control ticks injected with anti-HlFER2 antibodies, but not in the oocytes of Hlfer2-silenced ticks also injected with anti-HlFER2 antibodies. Our current findings suggest that host antibodies can be passed on to the oocytes, which is significant in formulating a vaccine that can disrupt tick reproduction.

Artificial feeding of Rhipicephalus microplus female ticks with anti calreticulin serum do not influence tick and Babesia bigemina acquisition

Ticks are obligate haematophagous ectoparasites considered the principal vectors of disease among animals. Rhipicephalus microplus and R. annulatus ticks are the most important vectors for Babesia bigemina and B. bovis, two of the most important intraerythrocytic protozoan parasites species in cattle, responsible for babesiosis which together with anaplasmosis account for substantial economic losses in the livestock industry worldwide. Anti-tick vaccines are a proved alternative to traditional tick and tick borne diseases control methods but are still limited primarily due to the lack of effective antigens. Subsequently to the identification of antigens the validation is a laborious work often expensive. Tick artificial feeding, is a low cost alternative to test antigens allowing achieving critical data. Herein, R. microplus females were successfully artificially fed using capillary tubes. Calreticulin (CRT) protein, which in a previous study has been identified as being involved in B. bigemina infection in R. annulatus ticks, was expressed as recombinant protein (rCRT) in an E. coli expression system and antibodies raised against rCRT. Anti-rCRT serum was supplemented to a blood meal, offered to partially engorged R. microplus females and their effect in feeding process as well as infection by B. bigemina was analyzed. No significant reductions in tick and egg weight were observed when ticks fed with anti-rCRT serum. Furthermore, B. bigemina infection levels did not show a statistically significant decrease when ticks fed with anti-rCRT antibodies. Results suggest that CRT is not a suitable candidate for cattle vaccination trials.

Tick capillary feeding for the study of proteins involved in tick-pathogen interactions as potential antigens for the control of tick infestation and pathogen infection

Background

Ticks represent a significant health risk to animals and humans due to the variety of pathogens they can transmit during feeding. The traditional use of chemicals to control ticks has serious drawbacks, including the selection of acaricide-resistant ticks and environmental contamination with chemical residues. Vaccination with the tick midgut antigen BM86 was shown to be a good alternative for cattle tick control. However, results vary considerably between tick species and geographic location. Therefore, new antigens are required for the development of vaccines controlling both tick infestations and pathogen infection/transmission. Tick proteins involved in tick-pathogen interactions may provide good candidate protective antigens for these vaccines, but appropriate screening procedures are needed to select the best candidates.

Methods

In this study, we selected proteins involved in tick-Anaplasma (Subolesin and SILK) and tick-Babesia (TROSPA) interactions and used in vitro capillary feeding to characterize their potential as antigens for the control of cattle tick infestations and infection with Anaplasma marginale and Babesia bigemina. Purified rabbit polyclonal antibodies were generated against recombinant SUB, SILK and TROSPA and added to uninfected or infected bovine blood to capillary-feed female Rhipicephalus (Boophilus) microplus ticks. Tick weight, oviposition and pathogen DNA levels were determined in treated and control ticks.

Results

The specificity of purified rabbit polyclonal antibodies against tick recombinant proteins was confirmed by Western blot and against native proteins in tick cell lines and tick tissues using immunofluorescence. Capillary-fed ticks ingested antibodies added to the blood meal and the effect of these antibodies on tick weight and oviposition was shown. However, no effect was observed on pathogen DNA levels.

Conclusions

These results highlighted the advantages and some of the disadvantages of in vitro tick capillary feeding for the characterization of candidate tick protective antigens. While an effect on tick weight and oviposition was observed, the effect on pathogen levels was not evident probably due to high tick-to-tick variations among other factors. Nevertheless, these results together with previous results of RNA interference functional studies suggest that these proteins are good candidate vaccine antigens for the control of R. microplus infestations and infection with A. marginale and B. bigemina.