Why just one tick bite can give you a fatal allergy to meat
DOCTORS are warning of a potentially deadly new allergy to meat which is spread by a bite from a tick.
The condition, first seen less than a decade ago, is believed to now affect thousands of Americans. But until recently it was not known that there were any victims in this country.
It has now been reported that at least six Britons have suffered severe reactions as a result of suffering a tick bite and then later eating meat. Poultry and fish do not cause problems, but victims can no longer eat beef, pork, lamb, venison, or other meats.
The allergy is caused when a tick bites deer, sheep, cattle, horses and pigs, and then bites a human. A substance in the tick’s saliva triggers our immune system to overreact to meat, which contains the same substance.
All mammals except apes and humans have a carbohydrate called galactose-alpha-1,3galactose (or alpha-gal) present in their flesh. But if you are bitten by a tick which carries alpha-gal in its saliva, then that bite will transmit alpha-gal into your bloodstream.
For reasons not yet fully understood, a delayed response then occurs in some individuals. So when that person eats meat at a later date, they suffer an allergic reaction, despite meat not having triggered problems previously.
This can sometimes only happen months later, leaving victims unaware of the source of the problem. To compound difficulties in diagnosis, the reaction usually occurs four to eight hours after eating meat.
In most cases it will cause hives, or urticaria, on the body, nausea or sickness. But it can trigger anaphylactic shock, which can be fatal, as it causes inflammation of the airways. An immediate injection of the hormone adrenaline is the only way to halt the process, which can kill in minutes. Up to 70 per cent of sufferers will have some kind of breathing problem during an attack.
In the UK, the allergy is spread by the same tick that carries the more widely known bacterial infection Lyme Disease, which can cause severe neurological and physical symptoms if not treated promptly with antibiotics.
The tick bite allergy was discovered by Professor Thomas Platts-Mills, a British consultant who has spent 30 years working in the United States. In 2012, Dr Nigel Kellow, a London spinal surgeon, was the first person in the UK to be diagnosed with alpha-gal allergy, six months after being bitten by ticks while on holiday on Dartmoor.
He has not eaten meat intentionally for four years but occasionally has done so accidentally. He carries an adrenaline injection shot called EpiPen in case he unknowingly eats something with meat in it and suffers an anaphylactic reaction. Dr Kellow said: ‘Soon after I’d been bitten I started getting these terribly itchy rashes after eating meat. I also felt nauseous and had a feeling of impending doom. I didn’t know what was causing it.’
Eventually he went to King’s College and the office of allergy consultant Dr Jonathan Brostoff – a friend and colleague of Professor Platts-Mills. A blood test confirmed that Dr Kellow was suffering alphagal allergy.
He said: ‘I haven’t had an anaphylactic shock but there’s always the risk. Occasionally I’ve been caught out by something with meat in it, such as some roast potatoes that were cooked in beef fat.
‘So I take the pen everywhere, particularly if I’m away travelling in a rural location such as Dartmoor, where medical help would be some time coming.’
Professor Platts-Mills, who works at the University of Virginia Medical School, was himself bitten in 2007 in the US, where ticks are widespread. He surmised that itchy rashes which erupted all over his body when he ate meat were linked to a mass of tick bites. ‘We proved it by developing a blood test demonstrating that I had been exposed to this blood sugar by a tick bite. I had been bitten by hundreds of ticks. I don’t know how many had the blood sugar, but I only needed one to become sensitised.’ Professor Platts-Mills, who published his discovery in The New England Journal Of Medicine, says 5,000 cases have been identified in the US, but believes thousands more remain undiagnosed. ‘We identified this reaction here but there has been very little publicity. People are being bitten all the time by the tick that causes this allergy.’
While ticks are often found in the countryside, the one carrying Lyme disease has been found on deer in London’s Richmond Park, and those spreading the meat allergy could be in the capital. Dr Malcolm Shepherd, a consultant in allergy at the West of Scotland Anaphylaxis Service in Glasgow, has seen six cases of anaphylaxis recently.
He said: ‘Allergy to meat can present in unusual and unexpected ways. Most allergies manifest very quickly, so if you are allergic to peanuts you will have a very quick reaction. But there is a delayed response to the meat allergen, so it was hard to trace back to the cause.’
Two patients in Glasgow both went into anaphylactic shock while they were sleeping, nearly four hours after they had consumed meat, said Dr Shepherd. Reported symptoms include itching, swelling of the mouth and wheezing, which had to be treated with a shot of adrenaline.
Dr Shepherd said: ‘We just don’t know how many people have it. Patients who present with it have suffered anaphylaxis, without it being immediately clear what was wrong with them.
‘First, it needs to be recognised. People won’t know the risk of eating meat. It could be something that is a big problem in areas where there is a prevalence of ticks.’
Walkers are advised to try to avoid wearing shorts and to check for ticks after walking in long grass.
If a tick is carrying the meat-conferring allergy, the bite is likely to be more itchy than a normal tick bite would be. And victims should suspect that they have become allergic to meat if they then discover rashes on their body.
Professor Platts-Mills said: ‘GPs might not know of this allergy yet. If you suspect you are a victim, ask to be referred to an allergy clinic where they can do a blood test.’