PlosOne jan. 2014 Hard Tick Factors Implicated in Pathogen Transmission Xiang Ye Liu, Sarah I. Bonnet Abstract Ticks are the most common arthropod vector, after mosquitoes, and are capable of transmitting the greatest variety of pathogens. For both humans and animals, the worldwide emergence or re-emergence of tick-borne disease is becoming increasingly problematic. Despite being such an important issue, our knowledge of pathogen transmission by ticks is incomplete. Several recent studies, reviewed here, have reported that the expression of some tick factors can be modulated in response to pathogen infection, and that some of these factors can impact on the pathogenic life cycle. Delineating the specific tick factors required for tick-borne pathogen transmission should lead to new strategies in the disruption of pathogen life cycles to combat emerging tick-borne disease. Introduction Ticks are the obligate blood-feeding ecto-parasites of many hosts, including mammals, birds, and reptiles, and are also vectors for several bacterial, parasitic, or viral pathogens. After mosquitoes, ticks are the second most common arthropod pathogen vector [1]. Recent intensification of human and animal movements, combined with socioeconomic and environmental changes, as well as the expanding geographical distribution of several tick species, have all contributed to the growing global threat of emerging or re-emerging tick-borne disease (TBD), along with increasing numbers of potential tick-borne pathogens (TBP) [2]. Despite an urgent requirement for in-depth information, the existing knowledge of tick pathogen transmission pathways is incomplete. Ixodidae possess the most complex feeding biology of all hematophagous arthropods [3], therefore the resulting difficulties in maintaining productive laboratory colonies doubtlessly explain a significant proportion of the gaps in our knowledge [4]. Moreover, because of the disadvantages of current TBD control methods (resistance, environmental hazard, increased cost), new approaches are urgently needed. Among these, vaccine strategies targeting those molecules that play key roles in vector competence are particularly promising [5], [6]. Consequently, research on molecular interactions between ticks and pathogens as well as the identification of suitable antigenic targets is a major challenge for the implementation of new TBD control strategies. During the blood feeding process, ticks confront diverse host immune responses and have evolved a complex and sophisticated pharmacological armament in order to successfully feed. This includes anti-clotting, anti-platelet aggregation, vasodilator, anti-inflammatory, and immunomodulatory systems [7]. For most TBP, transmission via the saliva occurs during blood feeding (Figure 1) and such tick adaptations may promote TBP transmission, notably by interfering with the host immune response 8–10. Moreover, during their development within the tick and their subsequent transmission to the vertebrate host, pathogens undergo several developmental transitions and suffer population losses, to which tick factors presumably contribute. Several studies have clearly reported that pathogens can influence tick gene expression, demonstrating molecular interaction between the vector and pathogen 11–24. Our review briefly outlines TBP transmission, highlights evidence of molecular interactions between hard ticks and TBP, and describes several tick molecules implicated in pathogen transmission. plosntds.org/article/info%3Adoi%2F10.1371%2Fjournal.pntd.0002566 FULL TEXT:
Posted on: Mon, 07 Apr 2014 21:11:49 +0000
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