Tick Bit by Matthew Goldberg (The Arcanist, June 2021) opens with this:
The ticks dropped down from the trees thick as sleet. I’d been out hunting with my brother, Paul, when it happened. They fell in great heaps, burrowing into us, tangling themselves up in our hair, our clothes. We had to shake them from our boots. Out they spilled, endless grains of living sand scouring our toes for blood. We found them days later under our armpits, the backs of our knees, the crannies of our earlobes. And then the telltale bullseye would emerge, hot and red. I’d gotten tick bites before, but never like this. I was a feast for an entire generation.
Subsequently the brothers are repelled at the thought of eating meat (or diary), and their similarly affected father—who persists—ends up in hospital due to a physical reaction.
We then see that ticks have spread all over the world, as has the condition that has affected the narrator’s family. The resultant rejection of animal products causes the collapse of those industries and a forced shift to a vegan diet.
The story finishes with the two brothers at the local creek. When they hear a rustling noise they don their ponchos as they think it is an approaching swarm of ticks, but (spoiler) it turns out to be a female moose and her calf coming down to drink—the first time that animal has been seen in the area for decades.
This is quite good as far as it goes, but it’s a very slight piece—an if-this-goes-on SF story compressed into a literary vignette. If this idea had been used in an genre SF story it would probably have been much longer, had multiple point of views,1 and would telescope through time from the beginning of the change to the end.
**+ (Average to Good)
1. The Grand Guignol version would have a thread which has an abattoir worker killing animals, being laid off, hitting rock bottom, and then returning to the factory to shoot himself in the head with a bolt gun.