Tick saliva and Its role in pathogen transmission

Ticks are major vectors of pathogens affecting both humans and animals worldwide and surpass all other arthropods in the variety of microorganisms—including viruses, bacteria, and parasites (protozoa and helminths)—they are able to transmit. They are strict hematophagous arthropods and pool feeders, ingesting all the fluids that are exuded into the wound generated by the bite. For most tick-borne pathogens (TBP), transmission occurs via the saliva injected alternately with blood uptake during the tick bite. This saliva is secreted by the tick salivary glands, which are implicated in several other functions that are essential to tick biology and development. Saliva is an essential bio-fluid for ticks, which dampens host defenses and facilitates the flow of blood to assure adequate feeding. It exhibits cytolytic, vasodilator, anticoagulant, anti-inflammatory, and immunosuppressive activities that, in addition, to underpinning blood feeding, provide a favorable context for transmission, survival, and propagation of TBP.