Epidemiological consequences of the ecological physiology of ticks

• Published in: Advances in insect physiology Vol. 37; pp. 297 - 339
• Main Author: Randolph, Sarah E
• Format: Journal Article
• Language: English
• Published: 2009
• Subjects: animal ecology; animal physiology; disease vectors; epidemiology; hematophagy; host seeking; Ixodidae; literature reviews; phenology; tick ecology; tick physiology; tick-borne diseases; ticks; vector competence; vector ecology; vectorial capacity
• ISSN: 0065-2806; 2213-6800
• DOI: 10.1016/S0065-2806(09)37006-X

The distinctive feature of ticks as vectors of pathogens is their strategy of taking only one very large blood meal per life stage. The consequence for ticks is that they are only periodic parasites, spending most of their time subject to ambient environmental conditions unprotected by the buffering effects of their hosts. This pattern of life demands certain unique physiological systems and also imposes certain constraints on the performance of ticks as vectors. The integument shows an unusual distribution of resilin to accommodate enlargement by one or two orders of magnitude over a few days while not compromising water-proofing. Unusually low rates of respiration and metabolism ensure long periods of survival without access to energy, but concomitantly slow development rates prolong those inter-stadial periods. Ticks are faced alternately with dehydration while off the host, and over-hydration while feeding; salivary glands provide the solution to both problems, and in doing so also provide a vehicle for pathogen traffic into a host site that is immunologically receptive to infection. Persistent cycles necessarily involve two life stages, one to acquire and the other to transmit; tick phenology determines the time course of pathogen transmission, and the climate-driven degree of seasonal synchrony between feeding life stages determines which pathogen types and strains can circulate.