One tick red meat can do without
Is there a tick/bandicoot connection to a cluster of Sydney people with a serious allergy to red meat? Bianca Nogrady reports
THEY were just ordinary pork spare ribs, properly cooked and harmless. But they were enough to land Peter Moore in hospital with a severe allergic reaction. ‘‘ It wasn’t instantaneous,’’ says Moore, 32. ‘‘ Maybe a couple of hours later I went to bed and woke up with hives, really big welts covering my body.’’
When he began having difficulty breathing, his wife rushed him to hospital.
Several months later it happened again, this time after a meal of meatballs, and then again a few months later after beef nachos. Moore had no known allergies and was in perfect health, which left him and doctors puzzled as to the cause. ‘‘ At the time, I wasn’t eating beef or pork at home so we stitched it together that it must be something in the meat, like a preservative or something,’’ says Moore.
But it wasn’t any flavouring or preservative — it was the meat itself.
Moore had developed a very rare allergy that whenever he eats red meat causes fullblown anaphylaxis, an extreme immune system response that can cause breathing difficulties, sudden drop in blood pressure, unconsciousness heart failure and even death.
And he’s not the only one. Nearly 50 adults living in one small corner of Sydney have become allergic to red meat, most of them in the past five years.
Sheryl van Nunen, head of the allergy department at Sydney’s Royal North Shore Hospital, first began noticing this strange allergy cluster around five years ago. The first patient with red meat allergy had actually appeared in her clinic nearly 20 years ago, but given the condition’s rarity, van Nunen assumed it was a once-in-a-lifetime case. She couldn’t have been more wrong.
‘‘ Then there’s a gap of some years, and then in the last five years there has been a deluge,’’ van Nunen says. Forty-nine adults have since come to her attention, all with severe allergy to red meat and almost all past or present residents of Sydney’s northern beaches, a district known as ‘‘ the peninsula’.
All these people react to beef, lamb, goat, and especially to venison, buffalo and kangaroo. The rarer the meat, the stronger the reaction. While some get a milder reaction causing vomiting and diarrhoea, most experience anaphylaxis. They range in age from 21-63 years old. There are slightly more women than men. Most patients are unrelated, although there are a handful of families where several members — not necessarily blood relatives — have the baffling condition.
Yet there are no obvious clues as to why such a large group of people from such a small area should develop such a rare allergy. ‘‘ They’re all sizes and shapes,’’ van Nunen says. ‘‘ The common thing is the geographic location.’’
But after the first few patients a pattern started to emerge. ‘‘ After you’ve seen a couple of people and the story’s the same, I like to my first question of you will be ‘ what happens a cause of tick-related allergy, a not uncomknow what’s happening to them so I always when you’re bitten by a tick?’,’’ she says. mon condition, particularly in tick-infested take a family history of allergy,’’. In one case, van Nunen saw a patient from areas. Perhaps there was cross-reactivity be-
This process turned up another important inner Sydney who was vegetarian but had tried tween the tick allergen and something in red commonality. Every single patient, bar one, red meat — with anaphylactic consequences. meat? had experienced a larger than normal reaction ‘‘ I said, ‘ you’ll think this is a very strange The possibility gave van Nunen another to tick bite. That is, they’d developed a 5-10 question, but have you ever had a large local thought: is there a connection between ticks centimetre-sized welt at the bite site. reaction or any reaction to a tick?’,’’ van and bandicoots? Bandicoots are omnivorous
Ticks are a particular problem along SydNunen recalls. It turned out the patient had marsupials, which happily eat meat, so it may ney’s northern beaches, especially the paralymoved away from the northern beaches be that when the tick bites the bandicoot, it sis tick so dreaded by pet owners. Ixodes precisely because of a problem with ticks. somehow acquires a meat-like allergen from holocyclus thrives in the moist gullies and Surprisingly, an allergy to two things at once the bandicoot. When that same tick then bites native bush of the Peninsula. Its numbers are — so-called ‘‘ cross-reactivity’’ — is fairly a human, that allergen could pass to the new boosted further by large populations of common. Patients allergic to, say, birch pollen host and sensitise them to red meat. resident bandicoots, which serve as unwilling may also react to apples, stone fruit and The answer could come from the United hosts for the tick. legumes. That’s so because there are similariStates. Ray Mullins, an allergy specialist in
The apparent link between a strong reaction ties between the reaction-provoking subCanberra, recently attended an allergy conferto a tick bite and red meat allergy seemed stances, or allergens, they contain. There are ence in Philadelphia where two presentations strange. But the more patients van Nunen saw, even documented cases of cross-reactivity were made that added more pieces to the the more she became convinced the connecbetween cow’s milk and beef allergies in puzzle. tion was real. children. Researchers investigating people with red
‘‘ It’s come to the stage now that if you come This raised the question in van Nunen’s meat allergy had discovered a new antigen — from (the northern beaches), particularly the mind as to whether there might be crossa substance that provokes an immune response peninsula, and you have an anaphylaxis and reactivity between ticks and red meat. Tick — in mammalian proteins. They called the you don’t understand why that occurred, then salivary allergen had already been identified as antigen alpha-Gal. Meanwhile, another team of researchers reported that they’d discovered an unusually high rate of allergic reactions to a particular cancer drug in certain parts of the country. This cancer drug also happened to contain alpha-Gal.
‘‘ There was a 10-fold higher chance that if you were being treated in these American states, you’d have an allergic reaction,’’ Mullins says. He suspects an environmental trigger in those states is sensitising people to alpha-Gal. Tantalisingly, ticks are endemic in those regions.
‘‘ It may be that there’s alpha-Gal in the tick and people get a tick bite and, for whatever reason, the person develops an allergic reaction to alpha-Gal in tick saliva,’’ Mullins suggests. ‘‘ Then the same substance present in something else they consume suddenly triggers a reaction.’’
Mullins says there was discussion at the conference about anecdotal evidence of a cluster of people who had developed red meat allergy after tick bite. However he has some reservations about the tick theory: ‘‘ When a person eats 25kg a year of red meat or more, why should a bite from a tick make you allergic to red meat?’’.
To find out, Suran Fernando, a clinical immunologist at Royal North Shore Hospital, is analysing blood from red meat allergic patients to work out exactly what allergen triggers their allergy. ‘‘ The burning question for me is, is this a true cross-reactivity,’’ says Fernando.
The only way to answer this question is to do laboratory studies to see if there is a common protein that people are reacting to, and because people react to more than one type of red meat, is this protein common to a variety of red meats, he says.
Some work has already been done overseas to tease out the allergen in red meat. ‘‘ Previous research (identified) something called bovine serum allergen,’’ Fernando says. ‘‘ The question is whether there is a protein in tick saliva that might be similar in structure to bovine serum allergen.’’ If so, this would suggest the tick saliva is indeed the culprit, and is sensitising people to react to the bovine serum allergen in the red meat.
Meanwhile, the Australian ‘‘ tick team’’ is keen to find more people such as Peter Moore, and monitor them to see if they develop red meat allergy. As well, van Nunen says she has a ‘‘ contract out on the bandicoot’’ to get some samples from a dead bandicoot and see if a common allergenic factor emerges
While many questions about the nuts-andbolts of red meat allergy remain unanswered, Peter Moore, for one, is relieved to have a diagnosis. ‘‘ For the previous five years I was just thinking it was a preservative, that I would never really know what the problem was,’’ says Moore. ‘‘ Now I know absolutely what it is, I’m much more careful.’’
Reaction: Peter Moore recalls a severe allergy to a tick bite not long before a meat meal brought him out in welts