Are ticks venomous animals?

Abstract

IntroductionAs an ecological adaptation venoms have evolved independently in several species of Metazoa. As haematophagous arthropods ticks are mainly considered as ectoparasites due to directly feeding on the skin of animal hosts. Ticks are of major importance since they serve as vectors for several diseases affecting humans and livestock animals. Ticks are rarely considered as venomous animals despite that tick saliva contains several protein families present in venomous taxa and that many Ixodida genera can induce paralysis and other types of toxicoses. Tick saliva was previously proposed as a special kind of venom since tick venom is used for blood feeding that counteracts host defense mechanisms. As a result, the present study provides evidence to reconsider the venomous properties of tick saliva.ResultsBased on our extensive literature mining and in silico research, we demonstrate that ticks share several similarities with other venomous taxa. Many tick salivary protein families and their previously described functions are homologous to proteins found in scorpion, spider, snake, platypus and bee venoms. This infers that there is a structural and functional convergence between several molecular components in tick saliva and the venoms from other recognized venomous taxa. We also highlight the fact that the immune response against tick saliva and venoms (from recognized venomous taxa) are both dominated by an allergic immunity background. Furthermore, by comparing the major molecular components of human saliva, as an example of a non-venomous animal, with that of ticks we find evidence that ticks resemble more venomous than non-venomous animals. Finally, we introduce our considerations regarding the evolution of venoms in Arachnida.ConclusionsTaking into account the composition of tick saliva, the venomous functions that ticks have while interacting with their hosts, and the distinguishable differences between human (non-venomous) and tick salivary proteins, we consider that ticks should be referred to as venomous ectoparasites.

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“…As such, the α-gal syndrome represents a potentially fertile area for discovery of mediators and pathways that govern type 2 immunity, an area of immunology that remains enigmatic. This premise would also be compatible with an emerging literature describing a protective role for type 2 immunity against venomous organisms, which arguably ticks represent [54–56]. …”

Antitumoral effects of Amblyomma sculptum Berlese saliva in neuroblastoma cell lines involve cytoskeletal deconstruction and cell cycle arrest

“…Ticks are specialized hematophagous ectoparasites of significant medical and public health importance (RANDOLPH, 2009). During the penetration process of the host skin, ticks succeed in blood feeding by manipulating the host's hemostatic, inflammatory, and immune defense mechanisms, due to numerous active components with pharmacological applications (CABEZAS-CRUZ & VALDÉS, 2014;RADULOVIC et al, 2014;STIBRANIOVA et al, 2013). As a source of anti-neoplasic compounds, it has been reported that tick saliva constituents can affect cancer cell proliferation (KAZIMIROVA et al, 2006), apoptosis (AKAGI et al, 2012, migration and invasion (POOLE et al, 2013), and tumor growth and angiogenesis (CARNEIRO-LOBO et al, 2009).…”

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“…One tick salivary substance that interferes with blood clotting is called Kunitz peptide. Kunitz peptides are small molecules that are also secreted by venomous organisms, such as scorpions and spiders, and they are an important component of tick saliva [4]. Tick salivary Kunitz peptides interfere with blood clotting, allowing the tick to slurp up its blood meal.…”