When my friend Peter first told me he was allergic to mammalian meat in 2008, I thought he was joking. I remember saying, “but we’re made of meat!”. His unusual story piqued my scientific curiosity, and set me on a journalistic path of enquiry that would span 13 years, several continents, multiple scientific disciplines, and four national and international publications.
My first piece on mammalian meat allergy and its unexpected link to tick bites was published in The Australian newspaper in 2008, and to my knowledge was the first story written about this allergy anywhere in the world.
At the time of that story, the Australian scientist at the heart of the story – Dr. Sheryl van Nunen – was working in relative isolation, still unaware that across the other side of the world, US researchers were working on their own part of the puzzle: the unusual prevalence of allergic reactions to the cancer drug cetuximab in the south-western United States.
A chance meeting at a scientific conference brought those two pieces of the puzzle together, revealing that the mediating factor was the molecule alpha-galactose, found in mammalian meat but not primate, and also present in cetuximab. For some reason – as yet unclear, ticks produce alpha-galactose and it is part of the many bioactive compounds found in their saliva. When they bite a host, a small amount of alpha-gal is injected, and in the occasional unlucky individual, this can prime their immune system to react to that sugar as if it were a threat.
What makes this particular allergy so special is that it provides the unique opportunity for scientists to study the development of an allergy in vivo. They know the trigger, the allergen and the outcome, which is enabling a detailed exploration of the immunological mechanisms that underlie allergies.
Coming back to this story again in 2020 for Nature, I expected that so many of the questions Professor van Nunen and others were asking would have been answered: why only some tick species, why only some people, why only some locations, why alpha-gal, why meat?
It was something of a joy to discover that this scientific story has only got bigger, more complex and more fascinating.
Not only has the number of cases of mammalian meat allergy/alpha-gal syndrome grown significantly, but it has been recognised in Australia, Europe, Japan, the United States and South Africa. It affects all ages and genders, people with or without a history of allergy, and the one common factor linking them all is an often severe reaction to red meat consumption.
There are more questions than answers. It’s unclear why the tick produces alpha gal: could it be a defence mechanism against its own parasites, or a response to environmental pressures? It’s also unclear why the distribution of these ticks and associated meat allergy is changing: is it because the hosts the ticks feed on are moving because of changing climatic conditions or other pressures? Why do some individuals develop the allergy after a tick bite while the majority do not: what is it about their immune response that suddenly reverses a lifetime of unproblematic meat consumption?
In this feature for Nature, I had the challenge of covering not just the allergy aspect of this story, but also the immunology, entomology, vector biology and zoology. I was trying to pull together often unconnected threads of medical practice and research around the world to paint as complete a portrait as possible of this new but increasingly prevalent condition.