Abstract
Ticks are ubiquitous blood-sucking ectoparasites capable of transmitting a wide range of pathogens such as bacteria, viruses, protozoa, and fungi to animals and humans. Although the use of chemicals (acaricides) is the predominant method of tick-control, there are increasing incidents of acaricide tick resistance. Furthermore, there are concerns over accumulation of acaricide residues in meat, milk and in the environment. Therefore, alternative methods of tick-control have been proposed, of which anti-tick cattle vaccination is regarded as sustainable and user-friendly. Over the years, tremendous progress has been made in identifying and evaluating novel candidate tick vaccines, yet none of them have reached the global market. Until now, Bm86-based vaccines (Gavac™ in Cuba and TickGARDPLUS™ Australia-ceased in 2010) are still the only globally commercialized anti-tick vaccines. In contrast to Bm86, often, the novel candidate anti-tick vaccines show a lower protection efficacy. Why is this so? In response, herein, the potential bottlenecks to formulating efficacious anti-tick vaccines are examined. Aside from Bm86, the effectiveness of other anti-tick vaccines is rarely assessed. So, how can the researchers assess anti-tick vaccine effectiveness before field application? The approaches that are currently used to determine anti-tick vaccine efficacy are re-examined in this review. In addition, a model is proposed to aid in assessing anti-tick vaccine effectiveness. Finally, based on the principles for the development of general veterinary vaccines, a pipeline is proposed to guide in the development of anti-tick vaccines.
Highlights
Ticks are ubiquitous blood-sucking ectoparasites capable of transmitting bacteria, virus, protozoa, and fungi to animals and humans [1,2]
Anti-tick vaccines are defined as tick proteins which are administered to a vertebrate host to induce antibodies with potential to bind and interfere with or inhibit (A) the tick salivary proteins that are secreted at the host–tick feeding site to promote tick pathogen transmission and/or blood acquisition through modulation of the host hemostasis and immune responses, and (B) specific or related proteins that are expressed in the tick tissues to promote its biological parameters
Based on the discussion regarding the effect of the prime vaccine dose on avidity and immune tolerance, two questions arise: (1) could it be that the administration of a high booster vaccine dose affects the avidity of the secondary antibodies, the anti-tick vaccine efficacy?; and (2) does administering half the prime vaccine dose as a booster vaccine dose confer a stronger humoral response? In other words, it is important that the above factors are taken into account when formulating efficacious anti-tick vaccines
Summary
Ticks are ubiquitous blood-sucking ectoparasites capable of transmitting bacteria, virus, protozoa, and fungi to animals and humans [1,2]. Unlike with the two- or three-host ticks, three out of the four stages of the one-host tick life cycle (larvae, nymph, and adult), are pre-exposed to the mode of treatment, for instance, chemicals or anti-tick vaccine-induced antibodies What this suggests is that, in comparison to the one-host ticks, the control of two- or three-host ticks would require a more expansive treatment approach in order to successfully interfere with the different stages of the tick life cycle. Anti-tick vaccines are defined as tick proteins which are administered to a vertebrate host to induce antibodies with potential to bind and interfere with or inhibit (A) the tick salivary proteins that are secreted at the host–tick feeding site to promote tick pathogen transmission and/or blood acquisition through modulation of the host hemostasis and immune responses, and (B) specific or related proteins that are expressed in the tick tissues to promote its biological parameters (tick feeding, egg laying, egg hatching, larvae, and/or nymph molting). The premise of this article is two-fold: (1) to highlight the bottlenecks to formulating efficacious anti-tick vaccines; and (2) to propose a model for conducting anti-tick vaccine effectiveness studies and a pipeline for assessing the vaccines from the bench to the field
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