For the past couple of decades, several people in tick-endemic regions of Australia and US have had to painstakingly alter their diet to avoid red meat, and sometimes even dairy products. They had been bitten. This was no vegan bug that had bitten them, but a blood-sucking tick: specifically, the lone star tick in the US or the paralysis tick in Australia. Something in these ticks’ saliva had remodeled their immune systems to reject red meat.
The link between tick-bites and red meat allergy was first published in 2009 by an Australian group of researchers led by Dr. Sheryl Van Nunen. Over the course of five years, Dr. Van Nunen had examined twenty-five patients from Sydney and New South Wales who presented with varying degrees of allergic reactions to red meat. She found that all of them had previously been bitten by the tick, and realized that this was the possible connection to their meat allergy.
Around the same time, Virginia-based scientists Thomas Platts-Mills and Scott Commins were investigating patients undergoing treatment with a cancer drug cetuximab. Some of the patients from the southeast states of the US developed itching and dizziness to the drug. The investigation demonstrated that these patients’ sera had antibodies specific to the drug even before they had started the treatment. Something in cetuximab was an allergen that their immune systems had previously encountered. But it wasn’t until the scientists fell foul of the lone star tick themselves did they make the connection between red-meat, cetuximab and tick-bites, and subsequently identified the allergen.
The culprit(s) are the tick, and alpha-gal. Alpha-gal (Galactose-alpha-1,3-galactose) is an innocuous enough carbohydrate molecule linked to proteins. It is synthesized in the bodies of nearly all mammals, with the exception of certain primates such as humans. Red meat is rich in alpha-gal; it’s also found in vaccines derived from bovine sources. The cancer drug cetuximab is synthesized in rats, and is therefore rich in alpha-gal moieties. The red meat allergy is in fact the body fighting against alpha-gal.
It is as yet unclear how exactly a tick-bite reprograms the human system to reject alpha-gal. So far, three species of ticks have been reported to effect alpha-gal allergy. Perhaps some component in these ticks’ saliva mimics mammalian alpha-gal. Or, as suggested by some immunologists, the tick could have transferred the alpha-gal to humans from its previous mammalian host.
When the human body reacts to the tick-bite, it is simultaneously rewired to fight alpha-gal or alpha-gal derivatives. This hypothesis could explain why not all people bitten by ticks suffer red meat allergy. However, at the current stage this appears to be only speculation. Dissecting the components of tick saliva, and pin-pointing the specific allergen if any, would be an important step in developing a therapeutic agent to counteract alpha-gal allergy.
Interestingly, ticks may not be the only species to trigger an allergic response to food. In 2015, a Japanese study reported cases of surfers becoming allergic to soybean-based foods after being stung by jellyfish. It would be interesting to uncover the underlying mechanism of how our immune system is triggered to translate an attack on the skin, to a specific allergic response against the same component in our food.
Rising numbers of red meat allergies
As long back as the 90s, clinicians and allergy specialists knew of patients who inexplicably developed allergic responses to red meat. Since then, incidence of red meat allergy or mammalian meat allergy (MMA) has been steadily on the rise around the world in various tick-prone areas. However, MMA is exceptionally high and appears to elicit more severe allergic responses along the north and east coasts of Australia.
Many patients develop severe anaphylactic shock following red meat consumption, which is rare in other parts of the world. As of now, it isn’t clear why this is so. MMA is also prevalent in the southern humid regions of the US. Last year, the Australian, US and UK media reported increasing numbers of people diagnosed with alpha-gal allergy. Dr. Scott Commins, who was part of the original investigation on cetuximab and alpha-gal allergy from the University of Virginia, stated that the increase was a true one. Allergy clinics were reporting higher numbers of cases of MMA than previous years.
The meat-allergy appears to be slowly spreading to the northern and western parts of the US as well. This could be due to spread of the lone star tick to other warmer regions in the US, or some other species of tick could be causing the allergy. Many tick populations are booming in the US possibly due to increasing global temperatures. Tick populations are rising in Australia as well.
In 2016, entomologist Stephen Doggett and Dr. Peter Banks from the University of Sydney posited that tick populations could be rising with increasing mammalian host populations (such as bandicoots and black rats). There is as yet no definitive evidence for what’s causing the increase in tick numbers.
With the possible expansion of the lone star tick’s geographical range in the US, it would be important to accurately diagnose and document cases of alpha-gal allergy. But doctors may find some difficulties in doing so, since red meat allergy differs from other food allergies. Patients suffer a delayed allergic reaction some 4-8 hours after meat consumption, which is unusual. Typically, food allergies present within shorter times. Many of the patients have no previous history of allergies. Repeated exposure to tick bites are likely to increase the likelihood of red meat allergy, and the severity of the allergic response. Further record and study of alpha-gal allergy would be required to understand the true scope of the tick-bite.
Researchers Platts-Mills, Commins and Wilson are working round the clock to chart the first of its kind distribution-map of red meat allergy in the US. This would be vital to spotting trends of overlap between tick distributions and alpha-gal allergy. In addition, Dr. Wilson is analyzing blood samples from newer incidences to find whether they need to beware of any other species of ticks.
In Australia where the alpha-gal allergy is most rampant, web resources from ASCIA (Australasian Society of Clinical Immunology and Allergies) list the types of tick allergies, diagnoses currently available and the precautions that may be taken for tick bites.
Since there is no cure yet, many patients hope that the allergy will fade over time provided they aren’t bitten by ticks again. There is some evidence to suggest that MMA does disappear in some people. In the meantime, epinephrine and a careful diet are the precautions recommended for the afflicted ones.