Most people who give up meat do so by choice, for ethical, religious or environmental reasons, but for some, it’s a lifestyle that’s forced upon them out of the blue, requiring a complete overhaul of how they eat. Foods like steak, hamburgers, sausages and pork chops can go from being weeknight staples to triggers for unpleasant – and in some cases, life-threatening – allergic reactions. The cause? A simple tick bite. (For more, watch "Tick Sick" on Insight, 8.30pm Tuesday November 14 on SBS).
The ticks turning people off meat
It sounds bizarre, but meat allergy from tick bites (called mammalian meat allergy or MMA) is a real medical condition, and one that has become increasingly prevalent in tick endemic areas of Australia, namely up and down the East coast of Australia, with ‘hot spots’ including Sydney’s northern beaches, the hinterland around Noosa in Queensland, and the South Coast of New South Wales.
“I saw my first patient with the condition in 1987, by around 2005 I’d seen about 23 people, then it started to increase almost exponentially to the stage where I’d be seeing two patients a week,” says Associate Professor Sheryl van Nunen of the Tick Induced Allergies Research and Awareness (TiARA) foundation. “The increase is likely multi-factorial, in that you’ve got more people living in those areas and more ticks coming into those areas,” says van Nunen. “There may even be a difference in the tick for all we know; perhaps it’s carrying something which helps people become allergic to it.” Beyond our shores, cases have also been reported in North America, Europe, Asia, Central America and Africa.
How the allergy develops
The tiny culprit causing the majority of mammalian meat allergy cases in Australia is the paralysis tick Ixodes holocyclus. In the gut of these ticks lurks the allergen, a sugar molecule called alpha-galactose (shortened to alpha-gal), which is picked up when the tick feeds on a host (for instance, a bandicoot or other small mammal), then injected into an unsuspecting human when the tick is pulled off.
“The tick bite sensitises the body a bit like a bee sting,” explains Dr Stephen Ginsborg, a GP on Sydney’s Northern Beaches*. “You could probably swallow a bee and it wouldn’t matter, but if a bee injects its sting into you, it has instant access to your immune system, and similarly tick bites mainline the allergen into the system.” Allergic reactions kick in when a person who has been injected with the allergen consumes alpha-gal, which is present in mammalian meats. Still, not everyone who is bitten by a tick goes on to develop mammalian meat allergy. “Proneness is a function of how people are set up genetically in regards to their immune system; some people will never be allergic to anything in their lives,” says van Nunen, who adds that the vast majority of people bitten by ticks don’t get MMA.
When symptoms strike
Mammalian meat allergy symptoms don’t always develop rapidly: they can appear months after a tick bite, and usually start three to six hours after eating meat, once alpha-gal is released from meat during digestion. “The least problematic although one of the most bothersome reactions is nasty abdominal pain, usually about three hours after eating,” says van Nunen. Symptoms can also include nausea, itching and hives, and at the severe end of the spectrum (requiring urgent medical assistance) is anaphylaxis, involving difficulty breathing, swelling of the tongue or throat, dizziness or collapse.
Curiously, people with MMA won’t necessarily have an allergic reaction every time they eat meat, and there are ‘amplifying factors’ that influence how severe a reaction is. “Some people only react if they have a glass of alcohol when they eat meat, some people have it if they exercise or if they’ve had non-steroidal anti-inflammatory drugs,” says van Nunen.
What’s off the menu
It’s not just mammalian meats (basically meats other than poultry) that are off the menu for people with MMA. Other foods containing mammal-derived products (think gravies, certain soups, stocks and sauces, rennet-containing cheeses and flavour ingredients in savoury packaged foods) can also trigger allergic symptoms. Some people also react to milk products and gelatine (found in jelly lollies, thickened gelatine desserts such as mousse, some yoghurts and even certain pharmaceutical products). While there’s no cure as yet, Ginsborg is quick to add that it’s not all doom, gloom and soy sausages forever. “After a while, some patients can start to slowly reintroduce meat under the direction of an immunologist,” he says.
The simple way to avoid MMA
If you’re not keen on becoming a vegetarian of circumstance, prevention is your best tactic. Wear a long-sleeved shirt and long pants if you’re gardening or bush walking in a tick-prone area, and carefully check for ticks afterwards. If you spot one, resist the urge to pluck it out with tweezers - this can squeeze the tick and cause it to transmit alpha-gal. “Our mantra for small ticks is ‘dab it, don’t grab it’, so gently touch a blob of Lyclear cream onto the tick and leave it for at least an hour for the tick to die,” advises van Nunen. “For a large tick, ‘freeze it, don’t squeeze it’, using an ether-containing spray and leaving it to drop off.”
The other take-away message is to ask your GP if you suspect you may have MMA, which is diagnosed with a blood test. “Anyone who has allergic symptoms or abdominal pain and has had tick bites should see their doctor and mention the possibility of mammalian meat allergy, because it’s not very well-recognised,” says Ginsborg.
*Please note: Dr Stephen Ginsborg is not currently taking new patients.