Biology and Molecular Biology of \u3ci\u3eIxodes scapularis\u3c/i\u3e

This chapter describes the biology of the tick Ixodes scapularis in relation to its role as the vector of the Lyme disease agent, Borrelia burgdorferi. Following a review of the internal anatomy of the tick, we review basic molecular processes that contribute to an understanding of the dynamics of the tick\u27s specialized parasitic processes, including attachment behavior, salivation; silencing of host anti-inflammatory responses to enable blood ingestion at the dermal feeding site; hemoglobin digestion and reproduction. The chapter is divided into three parts: 1) systematic and anatomical characteristics of ticks; 2) host finding, attachment, salivary disruption of host defenses, blood feeding and digestion; and 3) molecular regulation of tick bodily functions and reproduction. In the first part, we review the systematics of ticks and the taxonomic position of the vector of Lyme disease, I. scapularis, compared to other tick species. Next, we review the general organization of the tick body, including (a) the mouthparts essential for sucking blood, (b) the powerful sucking pharynx, (c) the midgut and its role in blood and hemoglobin digestion, (d) the salivary glands and their complex cellular organization, (e) the synganglion (a fused central nervous system) responsible for controlling all body functions, (f) the reproductive organs, and (g) the tracheal system that facilitates air intake and removal of CO2. In the second part, we highlight the role of the tick\u27s salivary glands in secreting a remarkably complex array of anti-hemostatic molecules that modulate the bite site in the host skin and how these salivary molecules facilitate the lengthy blood-sucking process. We also describe how ticks capture hemoglobin and internalize it in midgut epithelial cells for intracellular digestion, followed by the sequestration of heme into specialized hemosomes for disposal as hematin. We also will review the neural control of regulation of tick salivary glands, blood uptake, hemoglobin digestion, blood meal concentration, water/salt elimination, vitellogenesis and receptor mediated vitellogenin uptake in the developing oocytes and their oviposition