Just one bite from a lone star tick can spark a life-long allergy to red meat. This bizarre side effect has long been shrouded in mystery and misunderstanding, but a new study has taken a bold nudge forward in understanding the underlying mechanism that allows a humble tick to turn a BBQ-loving carnivore into a dedicated vegetarian.
The lone star tick, aka the northeastern water tick or the turkey tick, can be found across much of the eastern United States and Mexico. This aggressive tick needs to feed on the blood of humans, white-tailed deer, small mammals, and wild turkeys, in order to complete each stage of its life cycle.
Its bite is typically painless and often goes unnoticed, however, it occasionally leaves the host with a bacterial infection known as ehrlichiosis. In some unfortunate people, it can also spark an alpha-gal allergy, whereby the immune system reacts to alpha-gal, a carbohydrate found in most mammalian cell membranes. This means the person can no longer eat beef, dairy, pork, and lamb, although they can eat chicken and fish (and primate meat, for that matter) with no problem.
This is not your typical food allergy, however. For one, people can often test negative for meat allergies during standard allergy evaluations. People often have delayed onset of symptoms, such as the constriction of airways and a drop in blood pressure, occurring three to 8 hours after consuming the meat.
Reporting in The Journal of Immunology, scientists at the University of Virginia School of Medicine set out to find the key immunological changes in people who experience this unusual allergic reaction.
“We don’t know what it is about the tick bite that causes the meat allergy. And, in particular, we haven’t really understood the source of immune cells that produce the antibodies that cause the allergic reactions,” study author Loren Erickson explained in a statement.
“There’s no way to prevent or cure this food allergy, so we need to first understand the underlying mechanism that triggers the allergy so we can devise a new therapy.”
For the research, the team created an animal model of the meat allergy. Since rodents (the go-to for animal models) naturally produce alpha-gal, the researchers first had to genetically modify a bunch of mice to make them deficient in alpha-gal. They found that the immune response to alpha-gal was associated with having a huge number of a distinctive form of B cells, a kind of immune cell.
Many, many questions remain. For one, it's unclear how a superficial skin bite can lead to a loss of tolerance to alpha-gal in the gut. It also isn't understood why the meat allergy only emerges in some patients but not others.
However, armed with this knowledge about the B cells, the researchers hope they’re a step closer to understanding this curious affliction and perhaps nearing a viable treatment for it.
“This is the first clinically relevant model that I know of, so now we can go and ask a lot of these important questions,” Erickson concluded. “We can actually use this model to identify underlying causes of the meat allergy that may inform human studies."