Over 800 species of these obligate blood-sucking creatures inhabit the planet. They are second only to mosquitoes as vectors of human disease, both infectious and toxic. From the perspective of disease transmission to humans, the essential characteristic of ticks is their need to ingest a blood meal in order to transform to their next stage of development. Ticks accomplish this by perching in low vegetation and waiting for a susceptible host on which to attach and feed. Once on a host, the tick attaches its hypostome, a central piercing element with hooks, into the host's skin.
Some ticks secrete a cementing material to hold fast to the host.
In addition, Ixodes ticks secrete anticoagulant, immunosuppressive and antiinflammatory substances locally into the area of the tick bite. These substances presumably help the tick to accomplish its mission, which is obtaining a blood meal without the host's notice. These same substances also help any freeloading pathogens establish a foothold in the host. Ticks can carry and transmit a remarkable array of pathogens, such as bacteria, spirochetes, rickettsiae, protozoa, viruses, nematodes, and toxins. A single tick bite can cotransmit multiple pathogens, a phenomenon that has led to atypical presentations of some classic tick-borne diseases.