Abstract
Anti-tick vaccines have the potential to be an environmentally friendly and cost-effective option for tick control. In vaccine development, the identification of efficacious antigens forms the major bottleneck. In this study, the efficacy of immunization with recombinant ferritin 2 and native tick protein extracts (TPEs) against Ixodes ricinus infestations in calves was assessed in two immunization experiments. In the first experiment, each calf (n = 3) was immunized twice with recombinant ferritin 2 from I. ricinus (IrFER2), TPE consisting of soluble proteins from the internal organs of partially fed I. ricinus females, or adjuvant, respectively. In the second experiment, each calf (n = 4) was immunized with protein extracts from the midgut (ME) of partially fed females, the salivary glands (SGE) of partially fed females, a combination of ME and SGE, or adjuvant, respectively. Two weeks after the booster immunization, calves were challenged with 100 females and 200 nymphs. Blood was collected from the calves before the first and after the second immunization and fed to I. ricinus females and nymphs using an in vitro artificial tick feeding system. The two calves vaccinated with whole TPE and midgut extract (ME) showed hyperemia on tick bite sites 2 days post tick infestation and exudative blisters were observed in the ME-vaccinated animal, signs that were suggestive of a delayed type hypersensitivity (DTH) reaction. Significantly fewer ticks successfully fed on the three animals vaccinated with TPE, SGE, or ME. Adults fed on the TPE and ME vaccinated animals weighed significantly less. Tick feeding on the IrFER2 vaccinated calf was not impaired. The in vitro feeding of serum or fresh whole blood collected from the vaccinated animals did not significantly affect tick feeding success. Immunization with native I. ricinus TPEs thus conferred a strong immune response in calves and significantly reduced the feeding success of both nymphs and adults. In vitro feeding of serum or blood collected from vaccinated animals to ticks did not affect tick feeding, indicating that antibodies alone were not responsible for the observed vaccine immunity.
Highlights
Ixodes ricinus is a tick species which is widespread in Europe and can transmit various bacterial, protozoal and viral pathogens of medical and veterinary importance, including the causal agents of Lyme borreliosis, tick-borne encephalitis (TBE) virus and babesiosis
We aimed to investigate if immunization of cattle to reduce I. ricinus tick feeding and reproduction is possible
Serum from the tick protein extracts (TPEs) vaccinated animal did not clearly recognize IrFER2 (Figure 1). These results were confirmed by Western blot, which showed that immune sera from the TPE-immunized animal recognized midgut extract (ME), SGE and ovary proteins
Summary
Ixodes ricinus is a tick species which is widespread in Europe and can transmit various bacterial, protozoal and viral pathogens of medical and veterinary importance, including the causal agents of Lyme borreliosis, tick-borne encephalitis (TBE) virus and babesiosis. Multiple studies have shown that the incidence of both Lyme borreliosis and TBE in several European countries have increased over the last decades (Smith and Takkinen, 2006; Fulop and Poggensee, 2008; Sykes and Makiello, 2017; Radzisauskiene et al, 2018). Lyme borreliosis is the most common zoonotic vector-borne pathogen in the United States where I. scapularis, a sister species of I. ricinus, is the main arthropod vector (Schwartz et al, 2017)
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