By Sarah Zhang
José Ribeiro was 33 when he got his first tick bite, in the 1980s, and he remembers it as a momentous occasion. He had recently started studying tick saliva, a complex molecular cocktail that ticks inject into their hosts to inhibit pain, prevent blood clotting, and suppress the immune system—all so the tick can feed undetected for days and days and days. Ribeiro had been studying this in a lab, but now he was finally witnessing it in the flesh. In his flesh.
He marveled at the bite. It did not hurt. It did not itch. “I was amazed at how they could be so stealthy,” recalls Ribeiro, who now studies disease-carrying insects and ticks at the National Institute of Allergy and Infectious Diseases. Ticks use saliva to manipulate the body of their hosts so their bites stay painless, itchless, and as unobtrusive as a bug swelling with blood can be. Scientists have since cataloged more than 3,500 proteins from the saliva of various tick species.
Ticks evolved this molecular cocktail because they, unlike virtually any other blood feeder, feed for days at a time on a single host. Most tick species feed only once during each stage of their life cycle (larva, nymph, adult), so they have to get a “voluminous blood meal” out of each host, says Sarah Bonnet, who studies ticks at the French National Institute for Agricultural Research. A tick might even wait years between feedings. In the meantime, it must subsist entirely on its previous blood meal. Each meal counts for a lot.
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