Identification and Characterization of Immunodominant Proteins from Tick Tissue Extracts Inducing a Protective Immune Response against Ixodes ricinus in Cattle

Ixodes ricinus is the main vector of tick-borne diseases in Europe. An immunization trial of calves with soluble extracts of I. ricinus salivary glands (SGE) or midgut (ME) previously showed a strong response against subsequent tick challenge, resulting in diminished tick feeding success. Immune sera from these trials were used for the co-immunoprecipitation of tick tissue extracts, followed by LC-MS/MS analyses. This resulted in the identification of 46 immunodominant proteins that were differentially recognized by the serum of immunized calves. Some of these proteins had previously also drawn attention as potential anti-tick vaccine candidates using other approaches. Selected proteins were studied in more detail by measuring their relative expression in tick tissues and RNA interference (RNAi) studies. The strongest RNAi phenotypes were observed for MG6 (A0A147BXB7), a protein containing eight fibronectin type III domains predominantly expressed in tick midgut and ovaries of feeding females, and SG2 (A0A0K8RKT7), a glutathione-S-transferase that was found to be upregulated in all investigated tissues upon feeding. The results demonstrated that co-immunoprecipitation of tick proteins with host immune sera followed by protein identification using LC-MS/MS is a valid approach to identify antigen–antibody interactions, and could be integrated into anti-tick vaccine discovery pipelines.

Rickettsial survey and ticks infesting small mammals from the Amazon forest in midwestern Brazil

In the present study, samples of tick, tissue and blood from free-living wild small mammals (rodents and marsupials) captured in two municipalities from the Amazon biome of the Mato Grosso state, were molecularly tested for rickettsial infection. A total of 148 mammal specimens (46 rodents and 102 marsupials) were trapped, and 2,700 Amblyomma ticks (2,000 larvae and 700 nymphs) were collected. Ticks were recognized into four Amblyomma species: Amblyomma cajennense sensu stricto, Amblyomma coelebs, Amblyomma humerale, and Amblyomma scalpturatum, with new data for tick-host associations from small mammals in the Amazon biome. All tissue and blood samples of small mammals tested by PCR for rickettsial detection were negative. However, concerning tick-Rickettsia associations, Rickettsia amblyommatis was detected in all four tick species identified in the present study, being the first record for A. scalpturatum ticks. Furthermore, an uncharacterized species of Rickettsia belonging to the spotted fever group was detected in A. humerale as well.