Wonders of tick saliva

Abstract

The NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. AbstractSaliva of ticks is arguably the most complex saliva of any animal. This is particularly the case for ixodid species that feed for many days firmly attached to the same skin site of their obliging host. Sequencing and spectrometry technologies combined with bioinformatics are enumerating ingredients in the saliva cocktail. The dynamic and expanding saliva recipe is helping decipher the wonderous activities of tick saliva, revealing how ticks stealthily hide from their hosts while satisfying their gluttony and sharing their individual resources. This review takes a tick perspective on the composition and functions of tick saliva, covering water balance, gasket and holdfast, control of host responses, dynamics, individuality, mate guarding, saliva-assisted transmission, and redundancy. It highlights areas sometimes overlookedfeeding aggregation and sharing of sialomes, and the contribution of salivary gland storage granulesand questions whether the huge diversity of tick saliva molecules is 'redundant' or more a reflection on the enormous adaptability wonderous saliva confers on ticks.

Tick saliva and its role in pathogen transmission

“…Examination of single salivary glands of adult female I. ricinus confirmed expression of different clusters of genes at different times of feeding but also revealed differences between individual ticks [20]. As feeding ticks often cluster together on a host, they have the potential to pool their molecular individuality, which may help them feed [7]. Sharing of saliva resources has been demonstrated for male ticks as they "mate guard" their female mate [21].…”

“…In large ixodid tick species, the total volume of saliva secreted during 10 days of engorgement may exceed 1 ml [6]. At least seven "functions" can be attributed to tick saliva: water balance, gasket and holdfast, control of host responses, dynamics, individuality, mate guarding, and SAT [7]. Given that ixodid ticks increase their body mass 10-fold to 200-fold during engorgement, excretion of water and ions extracted from the blood meal is essential to maintain tick homoeostasis [6].…”

“…Considerable evidence relates to the immunomodulatory activities of tick saliva and, more recently, the dynamics of tick saliva-induced control of host responses ( Fig. 1); however, tick cement may contribute to SAT (vide infra) as may the individuality of ticks each with its unique sialome [7].…”

“…Orange arrows indicate saliva functions contributing (solid line) or potentially contributing (dashed line) to SAT of tick-borne pathogens. Blue dashed line indicates potential for SAT to contribute to feeding success of infected ticks (modified from[7])…”

Three-dimensional reconstruction of the feeding apparatus of the tick Ixodes ricinus (Acari: Ixodidae): a new insight into the mechanism of blood-feeding

“…They use their mouthparts to cut and tear into the skin, causing damage to blood vessels and dermal tissues. Secreting saliva that compromises their host's hemostatic processes, they effectively silence the host's awareness of their presence 3 , cement themselves to the skin 4 , and gorge themselves on the blood oozing around their mouthparts. Exactly how they accomplish these remarkable feats of parasitic nourishment has been the subject of intense study for many years and much has been learned using familiar microscopic instruments, chemistry, and molecular biology.…”