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Post-graduate training network for capacity building to control ticks and tick-borne diseases

Final Report Summary - POSTICK (Post-graduate training network for capacity building to control ticks and tick-borne diseases)

Ticks are vectors of many pathogenic viruses, bacteria and protozoa. They are of huge economic significance worldwide, and in the context of global warming, ticks and tick-borne diseases (TTBD) are on the rise, thus posing an increased risk to animal and human health. It is imperative therefore to build up training capacities to improve integrated control measures, including the development of efficient and appropriate vaccines. The POSTICK Initial Training Network (ITN) aimed to design new effective control strategies for TTBD through understanding of the mechanisms of tick-host-pathogen interactions, looking into pathogen diversity, survival and transmission, modulation of host immune reponses and tick survival and identification of host-pathogen-tick molecules for designing anti-tick vaccines and blocking pathogen transmission. The impact of the ITN relied on a complementary research programme covering different areas of tick-pathogen-host interaction, an innovative training programme and improvement of existing collaborations between industry and research centres and universities, thereby contributing to EU policies regarding the promotion of research and technology development, scientific cooperation and capacity building.

RTP1 focussed on two complementary aspects of the tick-borne bovine bacterial pathogen Anaplasma marginale, responsible for the disease anaplasmosis, which is endemic in tropical and subtropical areas worldwide. Many different strains exist, which vary in morphology, protein sequence, infectivity for ticks, antigenicity and pathogenicity. Four such strains form different geographic areas were characterised and compared at the genetic and antigenic levels. A Brazilian strain of low pathogenicity was compared with the existing Anaplasma centrale blood vaccine for ability to protect against a virulent Israeli strain of A. marginale. These studies emphasised the limitations of strain differences and the importance of stimulating an effective immune response in A. marginale vaccine development.

RTP2 examined the mechanisms underlying the modulation of the host immune response at the tick bite site and the allergenic potential of tick antigens. Study of tick bite site skin biopsies, human serum samples and in vitro assays revealed novel data on host cytokine expression and basophil activation and tick salivary immune inhibition during and after tick feeding in mice and humans.

RTP3 focussed on two economically important genera of tick-borne protozoa, Theileria and Babesia. Bioinformatic approaches yielded new information on mechanisms of life cycle stage differentiation and identified novel parasite surface antigens with potential application in transmission-blocking vaccines. In addition, development of species-specific diagnostic assays enabled assessment of the zoonotic potential of Babesia parasites circulating in Belgium.

In RTP4, two contrasting approaches examined tick cell innate defence responses to arbovirus infection. The first identified components of several antiviral innate immunity signalling pathways known from insects in tick cells and characterised their role in arbovirus replication. The second utilised whole transcriptome sequencing, proteomics and gene knock-down studies to identify novel tick genes and proteins that could be involved in tick innate immunity and cell stress responses to infection with tick-borne encephalitis virus.

RTP5 focussed on identification and characterization of tick proteins involved in tick-pathogen interactions resulting in several new candidate vaccine antigens for the control of vector infestations and pathogen infection. New protocols were developed to optimise the application of proteomics techniques to tick research, including a phylogenomics approach using de novo sequencing from proteomics data as a tool for the phylogenetic analysis of tick species in which sequence data is a limiting factor.

RTP6 examined the role of tick molecules in modulation of vector-host interactions. Six novel tick defensins with putative antimicrobial activity were identified and partially characterised. Glycoproteins were purified from cell lines derived from several tick species and their role in infection with tick-borne encephalitis virus examined.

RTP7 included development and optimisation of artificial feeding systems for different hard tick species, and studies on the tick-borne bacterial genus Ehrlichia. RTP7.1 established a relatively large-scale membrane feeding system for hard ticks which can be used successfully for screening potential acaricidal compounds and should also be applicable to tick-pathogen interaction studies. Conditions were optimised for at least one tick species, but the system was not suitable for all tested species and the unsuitability of artificial feeding for continuous tick colony maintenance was confirmed.

In RTP7.2a a novel Ehrlichia recently isolated from Brazilian ticks was cultivated in tick and mammalian cells and characterised by microscopy and phylogenetic analysis as a new species, designated Ehrlichia mineirensis.

RTP7.2b examined the effect of co-infection with an arbovirus on Ehrlichia canis kinetics in tick and mammalian cells in vitro. Presence of the virus did not significantly affect E. canis growth in tick cells, but presence of E. canis resulted in increased virus infection and replication rates on transfer from tick to mammalian cells.