A strange allergy to meat caused by ticks could be easier to catch than we thought


A solitary star female tick, or Amblyomma americanum.
Amanda Loftis, William Nicholson, Will Reeves and Chris Paddock (CDC)

One of the weirdest side effects of a tick bite – a new allergy to red meat – could be even easier to contract than previously anticipated. A new study published this weekend suggests that some tick bites can cause allergy, although they have recently been bitten. The discovery could reverse a widespread theory that ticks must be force-fed recently from the blood of other mammals before they can spread an allergy to meat in humans.

The allergy is caused by an immune response to a sugar molecule called alpha-gal. Most mammals have alpha-gal muscles, but not humans and other primates. For some reason, the bite of some ticks can sometimes trigger sustained hypersensitivity to products containing alpha-gal, including red meat, which includes beef, pork and even sometimes dairy products.

This hypersensitivity acts almost exactly like a typical food allergy, with symptoms such as hives, difficulty breathing or even life-threatening anaphylactic shock. But it's the only known food allergy to a sugar, not a protein, and its symptoms take hours to show after exposure. Sometimes the allergy does not appear until several years after the first bite.

We know the alpha-gal syndrome, as it's been called, for a long time. In fact, this is one of the main reasons why it is difficult to perform organ transplants in non-human animals such as pigs. But it took decades after the first cases of tick-transmitted alpha-gal were documented in the late 1980s for scientists to be able to trace them officially until the tick bite. And there is still so much that we do not understand about this state.

One of these mysteries is why exactly ticks can cause the syndrome. The lead author of the new research, Scott Commins, an associate professor of medicine and pediatrics at the University of North Carolina's School of Medicine, was one of the first doctors to report allergy cases to red meat a decade ago. A common theory that he and others have had is that ticks "pick up" the alpha-gal from a previous blood meal, such as a dog, a deer or a mouse . Their saliva, now filled with alpha-gal, then sensitizes the person that they are biting.

To test this theory, Commins and his team conducted a simple experiment. First, they took samples of human blood and filtered their native immunoglobulin E (IgE), the antibodies that protect against certain types of foreign invaders and also cause an allergic reaction to an allergen. They then dosed the blood with given plasma (filled with IgE antibodies) from people with or without the syndrome. Finally, they introduced the saliva of four species of ticks, the Lone Star, the deer, the Gulf Coast and the American tick. The saliva samples came from ticks that had not fed on blood containing alpha-gal.

So far, the tick most associated with allergy to red meat in the United States is the Lone Star tick. And as one could expect, the saliva of this tick could cause an immune response (based on the level of a certain white blood cell called basophil) 40 times higher than normal in blood sensitized to the # 39; alpha-gal. But the saliva of the deer tick, the main vector of Lyme disease and other tick-borne diseases in the United States, has also provoked a reaction. Most disturbing was that the undrained cat saliva of both species also caused a sensitized blood reaction.

The results, presented this weekend at the annual conference of the American Academy of Allergy, Asthma and Immunology (AAAAI), are preliminary (and have not yet been published in a peer-reviewed journal ). But they bring proof of another important theory stating that the tick itself, not its last meal, is at the root of the syndrome.

"These new data suggest that the last [theory] may be correct: something is in the saliva innately, "said Commins in Gizmodo. "All humans bring an existing response to alpha-gal and this data would be consistent with a pattern that tick bites would simply redirect the existing immune response to switch to an allergic response."

It is almost certain, according to Commins, that the odds of a single tick bite from a solitary star or other tick causing allergy are rather low. But we do not know how low that risk is right now (according to a previous estimate from Commins, there could be 5,000 people in the United States). And if ticks are the root cause, regardless of their diet, the window of opportunity for a bite causing an allergy will obviously be greater.

Allergy to red meat is just one of the nightmarish health problems caused by ticks – problems that, at least in the US, are likely to intensify as the climate warms. For example, nearly 60,000 cases of Lyme disease were reported in 2017, for example, compared with 22,000 in 2004. However, according to the CDC, the actual annual number of Lyme cases is around 300,000.

For example, while red meat allergy may be a rare tick-borne complication, this is one of many complications that are likely to become more common. And currently, there is no treatment or cure for the syndrome (some patients may eat meat again, but not all). This means that there is really only one way to prevent this from happening, according to Commins, although not all summer hikers are in danger.

"These results really highlight the importance of avoiding ticks and taking precautions to avoid tick bites," he said. "The people of the west and northwestern United States seem to have little or no risk. Beyond these areas, people need to be vigilant and diligent about precautions against tick bites. So we are very worried about the southern and eastern parts of the United States. "


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