Eight-legged bloodsucking freaks, no less.
Bad horror movie references aside, ticks are pretty creepy all by themselves. These arachnids get all their food from meals of mammalian blood, and are perfectly happy to nibble on humans.
More common? Sort of. More commonly-reported, anyway. Due to changes in habitat and climate, people are being bitten more often by ticks, so transmission rates are higher. Medical technology has improved, so doctors are able to figure out the cause of an illness is a tick-borne organism, rather than lumping it in with something else or not identifying it at all.
But stranger? Definitely! Being bitten by a Lone Star tick can induce an allergy to red meat in the victim. This is bizarre in many ways. It’s the first known allergy to a sugar rather than a protein, and the allergic reaction is delayed by three to six hours, rather than being immediate like most allergic reactions. And it is a true histamine reaction, one that may cause hives or even anaphylaxis.
It turns out the tick saliva contains a sugar also found in red (mammalian) meat, and people who have been bitten develop antibodies to that sugar that will also respond to their most recent meal. It takes some time for the sugar to move from the stomach into the bloodstream, thus the delay.
The strength of the reaction fades over time, as long as the person avoids being bitten by any more ticks.
What are the potential implications for humans dealing with climate change and greater exposure to tick-borne diseases? Or for humans on alien planets: being exposed to one thing could cause a reaction to something else. All sorts of unintended consequences are possible.