A combined transcriptomic approach to identify candidates for an anti-tick vaccine blocking B. afzelii transmission
Ixodes ricinus is the vector for Borrelia afzelii, the predominant cause of Lyme borreliosis in Europe, whereas Ixodes scapularis is the vector for Borrelia burgdorferi in the USA. Transcription of several I. scapularis genes changes in the presence of B. burgdorferi and contributes to successful infection. To what extend B. afzelii influences gene expression in I. ricinus salivary glands is largely unknown. Therefore, we measured expression of uninfected vs. infected tick salivary gland genes during tick feeding using Massive Analysis of cDNA Ends (MACE) and RNAseq, quantifying 26.179 unique transcripts. While tick feeding was the main differentiator, B. afzelii infection significantly affected expression of hundreds of transcripts, including 465 transcripts after 24 h of tick feeding. Validation of the top-20 B. afzelii-upregulated transcripts at 24 h of tick feeding in ten biological genetic distinct replicates showed that expression varied extensively. Three transcripts could be validated, a basic tail protein, a lipocalin and an ixodegrin, and might be involved in B. afzelii transmission. However, vaccination with recombinant forms of these proteins only marginally altered B. afzelii infection in I. ricinus-challenged mice for one of the proteins. Collectively, our data show that identification of tick salivary genes upregulated in the presence of pathogens could serve to identify potential pathogen-blocking vaccine candidates.
Ixodes ticks are small parasitic arthropods that feed on the blood of vertebrate hosts. They are three host-ticks; their lifecycle consists of four life stages, egg, larva, nymph and adult, where the latter three each parasitizes different hosts. Ticks needs to feed on blood of their hosts to obtain the nutrients and energy to develop into their next life stage or for successful reproduction. They do so by penetrating the skin of their host with their hypostome and, depending on the life stage, stay attached for 3–10 days to complete their blood meal. This feeding behavior presents a large window of opportunity for tick-borne pathogens to be transmitted to the host. Ticks are therefore only second to mosquitoes as the most important arthropod vectors for human disease. In contrast to the USA where Ixodes scapularis is the tick species most notorious for human disease1, in Europe, Ixodes ricinus is the tick that most affects human health2. I. ricinus is a vector for viruses, bacteria and protozoan parasites, and as such can cause a wide range of diseases, including tick-borne encephalitis, relapsing fever, anaplasmosis, babesiosis and most notably Lyme borreliosis.
Trentelman J.J.A., Šíma R., Krezdorn N., Tomás-Cortázar J., Barriales D., Takumi K., Butler J.M., Sprong H., Klouwens M.J., Urbanová V., Mahmood S., Winter P., Kopáček P., Anguita J., Hajdušek O., Hovius J.W. 2020: A combined transcriptomic approach to identify candidates for an anti-tick vaccine blocking B. afzelii transmission. Scientific Reports 10: 20061. [IF=3.998] Doi: 10.1038/s41598-020-76268-y