Tick spit protein may trigger allergic reactions

Ticks have had millions of years to figure out how to bite without triggering their victims' immune response. Proteins in the arachnids' spit evolved to manipulate immune cells so that the bloodsuckers can suck blood and transmit pathogens in peace. But these measures may not always have the desired effect when ticks bite humans, leading to severe allergic reactions, argue infectious disease specialists.