Les tiques pourraient déclencher une allergie à la viande

[habo]

Je sais, mais regardez la date, pas un premier avril.

http://discovermagazine.com/2012/jul-aug/09-how-a-tick-b!te-made-me-allergic-to-meat

En gros: donc déjà, on parle bien de déclencher une allergie nouvelle à l'âge adulte, ce qui est déjà rare. Là où cette allergie est exceptionnelle c'est que le déclencheur de l'allergie n'est pas une protéine, comme pour les allergies "normales", mais à une sucre, souvent dissous dans les graisses des mammifères, non présent dans la volaille. Ça rend le diagnostic très compliqué, la maladie étant très mal connue (mais on commence à parler d'épidémie dans le sud des états-unis) et le déclenchement des problèmes allergiques peut arriver plusieurs heures après la consommation de viande, les graisses mettant un bon moment à être assimilées.

Le point rassurant? Le problème n'a pour l'instant été identifié qu'avec des variétés de tiques américaines et australienne...

Edit: remplacer le '!' dans b!te par un 'i' pour que le lien fonctionne, le filtre anti profanité a sévi. Ou si un modo peut réparer ça.

[VERDUG0]

Ton lien est incomplet.

EDIT: j'arrive pas a y acceder, tu pourrais resumer ou copier/coller?

Merci

[Djeep]

Ton lien est incomplet.

EDIT: j'arrive pas a y acceder, tu pourrais resumer ou copier/coller?

Merci

BJR  Lien pas mort http://minu.me/6utu   HN

How a Tick b!te Made Me Allergic to Meat

A disastrous allergic reaction sends the author looking for immunological answers.
by Helen Chappell

published online August 13, 2012

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nullDelicious. But deadly.

Hamburger image via Shutterstock

The last time I ate a hamburger, I spent the night in the emergency room. There wasn’t anything wrong with the hamburger itself—aside from being a bit overdone—but it sent me into anaphylactic shock.

It wasn’t always this way. Before last July’s “Hamburger Incident,” as I’ve come to think of it, meat and I had a long and happy history together. I grew up in a steak-and-potatoes sort of family, and one of my proudest achievements is chowing down on llama meat when I was on a college trip in South America. At the time of the Hamburger Incident, I had just returned to my native North Carolina after three years’ exile in the West, and I was looking forward to eating proper pulled pork barbecue again almost as much as I was looking forward to seeing my family.

Unbeknownst to me, a recent bug b!te had squelched my dreams of greasy, vinegar-sauced deliciousness. It turned out, I eventually learned, that thanks to a single nip from Amblyomma americanum, the lone star tick, I was now violently allergic to meat.
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The fact that tick b!tes can cause a meat allergy is still relatively unknown. For that matter, the fact that people can develop allergies as adults, rather than having them since childhood, is still relatively unknown, though it’s not unheard of to become allergic to shellfish or walnuts later in life. As a long-time sufferer of dust-mite allergies myself, I always believed allergies were something I’d grow out of, not into.

Unfortunately, I’m not alone in developing a meat allergy. A pile of evidence has amassed over the past several years proving that there are many others. I was hoping for some reassurance when I spoke with Dr. Scott Commins at the University of Virginia about the allergy. “We believe this is becoming an epidemic in the South,” he told me instead. There aren’t any published estimates yet of the prevalence of the allergy, but anecdotal evidence makes it clear that there are a whole lot of us missing out on our barbecue.

Commins is one of a few scientists who are starting to tease out some of the details of the allergy. So far, they’ve proven that lone star ticks, a common species in the Southeast, can trigger the allergy, but they suspect other species of ticks can as well. The same allergy has been observed in Australia, for instance, where there are no lone star ticks to spread it.

Not every b!te from a lone star tick necessarily causes the allergy. The b!te I blame for my allergy wasn’t my first tick b!te—not by a long shot—or even my first that summer. Having grown up in the woods, I’m so used to tick b!tes that I don’t even notice them half the time. But I remember this particular b!te because it left an itchy welt behind that lasted for weeks after I’d tweezed out the tick itself. Long-lasting, itchy welts, I now know, are one of the hallmarks of an allergy-causing tick b!te.

So how does a tick’s b!te transform your immune system into a meat-attacking machine? Tick saliva is “a really good provocateur of an immune response, even outside of an infection,” Commins told me, though they are not yet sure whether it’s bacteria carried in tick saliva or the saliva itself that is responsible. But they believe that something in some ticks’ saliva stimulates the human immune system to produce antibodies to a sugar present in mammalian meat, though not poultry and fish, called galactose-alpha-1,3-galactose (alpha-gal for short). The next time an unsuspecting meat lover chows down on a hamburger, those antibodies could rally a systemic allergic reaction.

As if the whole idea of a tick-induced allergy isn’t bizarre enough, the fact that alpha-gal is a sugar, not a protein, is particularly odd, says Commins. Most allergies are immune responses to proteins—peanuts, for instance, contain proteins that link up with antibodies in people who are allergic, triggering a reaction. To date, alpha-gal allergy is the only known case of a sugar-triggered allergy.

Even stranger, although most allergic responses are immediate, the reaction to alpha-gal is delayed by several hours. The delay, I can testify, was one of the most confusing things about my Hamburger Incident. I ate the fateful burger somewhere in South Carolina on my way home from a backpacking trip, but I didn’t develop any symptoms at all until I had driven hundreds of miles northward. Even then, my symptoms came on slowly, starting with hives that stubbornly resisted all the antihistamines I could throw at them, and eventually progressing to facial swelling, dizziness, and wheezing. Once my eyes started swelling shut, I decided to drive myself to the hospital.

(A public service announcement: Don’t do that. Even if you don’t crash your car, you’ll get scolded by the emergency room staff. And besides, you’ll need a ride home anyway once they shoot you full of intravenous antihistamines.)

But back to the delayed reaction: it’s part of what makes it so hard for people with this allergy to figure out what’s making them sick. You can have a steak for dinner and not know anything’s amiss until the middle of the night. Add to that the fact that different kinds of meats—or even different cuts of the same kind of meat—can cause more or less severe reactions, and you’ve got a recipe for confusion.

“It certainly takes longer than the average allergy [to figure out],” Commins told me. “Sometimes it takes years.”

Commins and his colleagues suspect that the delay could be a key to figuring out what is going on, though. They believe it might not be the body being slow to mobilize its response, but rather the allergen taking a while to put itself in the immune system’s way. “We think it has to do with the fat,” he says, “because…the fat takes anywhere from three to five hours to hit the bloodstream.”

Add to that the anecdotal evidence that some patients can tolerate lean meats and others get sick from eating pork rinds (which, oddly enough, don’t contain any actual meat at all, only fat), and alpha-gal molecules riding on fat are a strong contender for explaining both the unusual delayed reaction and the fact that it’s triggered by a sugar. Sugars, unlike proteins, have trouble sticking to enough antibodies to cause an allergic reaction. Fat molecules, however, might help make alpha-gal sticky enough to get he process started. But it’ll take more research to know for sure.

In the meantime, education is a priority. The allergy is so bizarre and still so unknown that not only do sufferers struggle to figure out why they’re getting sick, their doctors do too. When I spoke with Commins’ colleague Dr. Tom Platts Mills after the Hamburger Incident, he told me, “Most of the patients who come to see us are looking to be reassured they’re not mad.”

I was lucky in that respect. My doctor has been practicing medicine in tick country for decades. Though she had never seen an allergy like mine before, when I pitched my tick-b!te-meat-allergy theory to her, her response was wry: “At this point, I’d believe ticks could do almost anything.”

As for myself, I’ve now spent more than a year trying to avoid beef and pork, though here in the South, bacon seems to constantly sneak its way into places it doesn’t belong (a dish of Brussels sprouts being my most memorable example). When Dr. Commins told me about studies in which he and his collaborators feed patients a sausage biscuit and draw their blood every hour until they have a reaction, it made my mouth water. Any chance I could participate?

Nope. “I try to pick people who haven’t had those ‘I’m gonna die’ reactions,” he replied.

Too bad. I really wanted that sausage biscuit.

Helen Chappell is a museum exhibit developer and freelance writer based in Durham, North Carolina.