Gaining a Better Understanding of Ticks' Salivary Glands to Fight Them More Effectively

Ticks are parasites that carry many diseases, including Lyme disease, tick-borne meningoencephalitis, and Crimean-Congo hemorrhagic fever, to name just a few. The best way to prevent these diseases is to take action against the ticks that cause them. Studying these tiny creatures could lead to new, more targeted, and environmentally friendly strategies. While our interaction with ticks—and, by extension, the most vivid memory we often have of them—is limited to the moment they feed on blood, the tick’s parasitic stage is actually only a small part of its life cycle. For the vast majority of its life, the tick remains in a non-parasitic, fasting state in tall grass. Over a 3-year life cycle, the European castor bean tick (Ixodes ricinus) and the North American black-legged tick (Ixodes scapularis)—which are the primary vectors of Lyme disease—take only one blood meal at each of their blood-feeding stages (larva, nymph, and adult female) to facilitate molting into the next stage or to lay eggs. They thus go from one extreme to the other—first engorged with blood, then completely drained. Throughout their lives, the survival of ticks therefore depends heavily on the effective maintenance of water homeostasis. They are highly sensitive to dehydration. The osmoregulatory role of ticks’ salivary glands is therefore naturally crucial before, during, and after their blood meals. The survival and persistence of ticks in the environment depend on the activity of these glands. Researchers therefore sought to deepen our understanding of these glands. Until now, studies have focused on the tick’s blood meal, during which the secretory activity of the salivary glands is most evident. Thus, catecholamines (dopamine and norepinephrine) and the cholinergic agent pilocarpine have been shown to be powerful activators of saliva secretion in ticks. A new study supports these findings by analyzing the ultrastructure and function of cholinergic synapses in the salivary glands of both tick species. The authors were able to demonstrate the relationship between cholinergic neurons and the salivary glands. They subsequently identified and characterized the molecular structure and function of two cholinergic receptors in these salivary glands. The authors also investigated the role of this cholinergic pathway during water intake by ticks following periods of desiccation. They tested in vivo whether disrupting components of the cholinergic synapse in tick salivary glands affects water intake in severely dehydrated ticks. This is the first time that the cholinergic innervation of tick salivary glands has been described, suggesting that it plays a role in water uptake by ticks in a desiccated state, and that the signaling pathway between specific neurons in the tick’s central nervous system (synganglion) and its salivary glands has been identified. This pioneering study paves the way for the development of new, targeted methods for tick control, particularly environmentally friendly strategies.