Tick saliva: recent advances and implications for vector competence

Abstract

Secretions of the tick salivary glands are essential to the successful completion of the prolonged feeding of these ectoparasites as well as the conduit by which most tick-borne pathogens are transmitted to the host. In ixodid ticks the salivary glands are the organs of osmoregulation, and excess water from the bloodmeal is returned via saliva into the host. Host blood must continue to flow into the feeding lesion as well as remain fluid in the tick mouthparts and gut. The host's haemostatic mechanisms are thwarted by various anti-platelet aggregatory, anticoagulatory and anti-vasoconstrictory factors in tick saliva. Saliva components suppress the immune and inflammatory response of the host permitting the ticks to remain on the host for an extended period of time and, adventitiously, enhancing the transmission and establishment of tick-borne pathogens. Over the years much work has been done on the numerous enzyme and pharmacological activities found in the tick saliva. The present article reviews the most recent work on salivary gland secretions with special emphasis on how they favour pathogen transmission.

Biological Transmission of Arboviruses: Reexamination of and New Insights into Components, Mechanisms, and Unique Traits as Well as Their Evolutionary Trends

“…It has been speculated that the pharmacologic substances in the saliva of ticks either immunosuppress vertebrate hosts with antiinflammatory and antihemostasis molecules or introduce a variety of chemicals to suppress defense mechanisms of vertebrate host by targeting natural killer and interferon synthesis (36). Alternatively, the function of the tick salivary gland extract substances was hypothesized to be maintenance of fluidity of the blood as it passes through the mouthparts and into gut rather than inhibition of blood coagulation at the feeding site (30).…”

The reproductive success of the parasitic bat fly Basilia nana (Diptera: Nycteribiidae) is affected by the low roost fidelity of its host, the Bechstein’s bat (Myotis bechsteinii)

“…However, ectoparasites can increase the costs of reproduction (Møller 1993;Bize et al 2004), cause energetic costs (Giorgi et al 2001), evoke the risk of disease transmission (Durden et al 2004;Bowman et al 1997) and may negatively influence growth and development (Fitze et al 2004). Infestation with louse flies (Hippoboscidae) has negative effects on the condition of birds (Blanco et al 2001), and similar effects can be assumed for bat flies, which are closely related to louse flies but infest bats instead of birds.…”

Identification of an IL-2 Binding Protein in the Saliva of the Lyme Disease Vector Tick, Ixodes scapularis

“…Of all the blood-feeding vector arthropods, hard ticks, by virtue of their protracted feeding period, represent an extreme example of evasion of their host's hemostatic defenses and immune response (5)(6)(7)(8). Ticks are obligate bloodfeeding ectoparasites, with many species remaining attached for periods of 3-15 days (9,10). Many tick species are important vectors of disease worldwide.…”

“…Ixodes scapularis is the main North American vector of Lyme disease, now the most prevalent vectorborne disease reported in the United States (11), as well as human granulocytic ehrlichiosis and babesiosis (12)(13)(14)(15). Because ticks deliver the molecules used to confound host defenses in their saliva, this secretion is an important feeding and vector competence factor for these ectoparasites (9).…”