For many people it would be their worst nightmare, but for some it is a reality. After being bitten by a tick, some people develop an allergy to red meat. So severe is this allergy that it can cause people to drop into potentially life-threatening anaphylaxis, where the airways constrict and your blood pressure plummets. Only very recently have doctors figured out what is going on, and according to some, the prevalence of such a reaction is worryingly on the up.
The immune reaction is not actually to the meat protein, but a sugar that is only found in non-primate mammals, meaning that it is not found in humans. Occasionally when the tick then bites a human after having fed on another mammal, the insects saliva is mixed with this sugar, so that when the body launches an immune response against the tick, there is a crossover between what the body thinks it is fighting. This means that when a person then eats red meat, and sometime even dairy products, the body can sometimes detect the sugar and launch an immune response against it.
The sugar is known officially as Galactose-alpha-1,3-galactose, or more simply alpha-gal. While there have been hints that this has been occurring for decades, it was not formally described until 2007 by Australian doctor Sheryl van Nunen, who spent years documenting the curious link between tick bites and meat allergy, which is usually incredibly rare, in and around the northern beaches of Sydney.
Those with the allergy cannot eat any red meat, including beef, lamb, pork or goat, but can eat other meats such as poultry and fish. Pavel Ilyukhin/Shutterstock
Van Nunen discovered that each of the patients who came to see her with the allergy had one thing in common: At some point in the past they had had a large allergic reaction to a bite from the paralysis tick Ixodes holocyclus. This could have occurred months before they were then taken ill after eating red meat, and the allergic reaction to the meat doesn’t usually occur until hours after having consumed it, so the link between the tick and the allergy was not immediately clear.
It turns out that this bizarre reaction occurs around the world. In the US, there is a hotspot in North Carolina, for which a large population of white tailed deer coupled with the lone star tick (Amblyomma americanum) is responsible, while in Europe the castor bean tick (Ixodes ricinus) is implicated. But it’s not only eating red meat that can cause the reaction.
The allergy was in fact first brought to the attention of doctors in the US when cancer patients started having severe allergic reactions to the drug Cetuximab. Developed from a mouse cell line, Cetuximab also contains alpha-gal, which the patients were reacting to. It was in part after seeing Dr van Nunen’s research that they make the connection, and found that when they mapped the distribution of patients allergic to Cetuximab with that of the lone star tick, it almost exactly matched.
It is now thought that around 600 people suffer from the allergy in Sydney alone, with Dr van Nunem reporting that she is now dealing with around two cases per week. She warns that precautions should be taken when in areas of high tick prevalence, such as wearing bug spray and knowing how to safely remove them if bitten.
