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Ticked Off About a Growing Allergy to Meat
16 November 2012 5:43 pm
Tick bites have long been synonymous with bad news, responsible for transmitting diseases such as Lyme disease, Ehrlichiosis, and Rocky Mountain spotted fever, but this must be a carnivore or BBQ lover's worst nightmare. A growing body of research suggests that bites from a particular tick are causing an unusual allergic reaction to meat. At an allergy meeting last week, for example, a diagnostics lab presented evidence that the highest prevalence of the allergy is in the southeastern United States, where the tick primarily thrives. Yet American BBQ lovers and carnivores elsewhere may not rest easy; the allergy mysteriously afflicts people living in parts of the United States, even Hawaii, where the tick does not live.
The meat allergy, known as alpha-gal for a sugar carbohydrate found in beef, lamb, and pork, produces a hivelike rash—and, in some people, a dangerous anaphylactic reaction—roughly 4 hours after consuming meat. But unlike other common food allergies, the alpha-gal allergy has been found only in people who have been bitten by ticks—specifically the lone star tick, previously best known for causing a condition called southern tick-associated rash illness, the symptoms of which include rash, fatigue, headache, fever, and muscle pains. "You have to have a tick bite to then trigger the immune reaction," Stanley Fineman, an allergist and president of American College of Allergy, Asthma and Immunology (ACAAI).
People who are bitten by the ticks develop antibodies against the alpha-gal sugar, and individuals with symptoms can be diagnosed by a blood test that looks for the presence of those antibodies. But Fineman says that too few people are aware of the allergy or don't make the connection between a case of hives and the meal they had much earlier in the day, and so they never get tested. "It takes 4 to 6 hours to see a reaction, so many people don't correlate that to their meat, or hamburger or something. It's easy to miss," Fineman says.
Allergy researcher Thomas Platts-Mills of the University of Virginia (UVA) in Charlottesville has been studying the alpha-gal reaction since 2002, when he began investigating an unusual sensitivity to the cancer drug cetuximab, which contains the same alpha-gal sugar as meat. Cancer patients who demonstrated an allergic reaction to the drug were nearly exclusive to the southeastern United States and were also found to have high levels of alpha-gal antibodies, Platts-Mills explains. Furthermore, some of them, along with other noncancer patients in the same region, also reported having severe allergic reactions after eating meat. Platts-Mills later published the relationship between alpha-gal antibodies and the cetuximab allergy in The New England Journal of Medicine.
But Platts-Mills only began to suspect the connection between the alpha-gal antibodies and the ticks after he was bitten by several ticks while hiking and contracted the allergy himself in 2007. His antibody levels jumped significantly after the tick bites, he found. In 2009, he and UVA colleague Scott Commins reported the link between alpha-gal and the meat allergy in The Journal of Allergy and Clinical Immunology—and suggested a possible link between the ticks and alpha-gal based on a more than 80% rate of reported tick bites among the patients before exhibiting symptoms.
In 2011, Platts-Mills and others were able to confirm that the bites cause an increase in alpha-gal antibodies. But so far, he says, no one is sure exactly which substance in the tick saliva is responsible for the development of alpha-gal antibodies.
"Tick saliva is brilliant stuff. It has loads of substances, but if you ask me which substances are critical, I don't know. It's something we are working on," Platts-Mills says.
Although the initial cases of alpha-gal allergy were found in lone star tick-laden regions, incidences of the allergy are no longer limited to this tick's favorite haunt, says Michelle Altrich, the clinical laboratory director of Viracor-IBT Laboratories, one of two main reference labs offering a diagnostic assay for the alpha-gal allergy. Last week, at ACAAI's annual scientific meeting in Anaheim, California, researchers from Viracor revealed that although the highest number of reported cases of alpha-gal allergy were found in the southeastern United States, the allergy—which has affected about 1500 people and counting—has also been seen in large numbers well outside known lone star tick areas.
"We were curious to know whether the prevalence of the allergy actually overlaid with the tick or if it was different," Altrich explains. Of the samples submitted for testing, she says, "we saw a trend in positive results to the southeastern U.S. with the tick, but interestingly we also found positive rates varying from 4% to 23% outside of the tick area. We've actually had positives as far west as Hawaii." Why that is isn't clear, Altrich says. One possibility is that those diagnosed with the allergy in places like Hawaii were actually bitten while traveling in a high-tick area like Tennessee, she says.
Another possibility is that the ticks are growing in number and their territory is spreading to adjacent states. The distribution, range, and abundance of the lone star tick has increased steadily in the past 20 to 30 years, according to the U.S. Centers for Disease Control and Prevention—likely concurrent with an explosion of populations of deer, the tick's primary host. Platts-Mills says the increasing number of cases may also be explained in part by the sheer number of bites inflicted by this particular species of tick. "This tick is very aggressive. Its larval forms will bite humans, whereas none of the other American tick larvae will do that," he says.
Preventing the tick bites is the only way to stop the allergy before it starts—but Platts-Mills says once a person has the allergy, there is some evidence that if they don't continue to get bitten they will eventually get better. But until then, it's best to pass on the BBQ.