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Ticks: parasites and disease vectors Although it is early days, the interpretation of genome Editorial TRENDS in Parasitology Vol.23 No.9Ticks, as blood-feeding ectoparasites, affect their hosts both directly and as vectors of viral, bacterial and protozoal diseases. Their impact as disease vectors on human well-being is second only to that of mosquitoes, and their effect on livestock, wildlife and domestic animals is immeasur-ably greater [1]. An important source of information on ticks and tick-borne pathogens is described in Box 1. The tick’s mode of feeding means it must maintain intimate contact with the host in the face of host defensive responses for a protracted time. In the tick–host–pathogen triangle, we therefore have the cut and thrust of parasite attack, host response and parasite counter-response, and the interactions between transmitted pathogen and th