Your Weekly Checkup: Ticks May Make You Allergic to Meat

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In a column several months ago, I wrote that illnesses caused by the bite of an infected mosquito, tick or flea (vector-borne diseases) have more than tripled in the United States from 2004 to 2016. I noted that the usual diseases spread by ticks such as Lyme disease, Rocky Mountain spotted fever, and tularemia; and mosquitoes, which transmit West Nile virus, Zika, dengue, and chikungunya, were increasing.

I did not discuss a fascinating, relatively newly described entity called tick-borne meat allergy.

Several types of ticks, including the lone-star tick (females have a distinctive white mark on their backs) common in southeast parts of the U.S. have been demonstrated to cause an allergic reaction to ingested meat. Affected individuals become allergic to a complex sugar compound called galactose-alpha-1,3-galactose, or alpha-gal (AG) for short.

When the lone-star tick feeds, AG leaks from its mouth into the wound, exposing the victim’s immune system to the sugar and an enzyme in the tick’s saliva, prompting the immune system to remember and pursue AG at the next exposure. AG is normally part of our cell membranes, but under certain circumstances, if the immune system learns to see AG in the mammalian meat we eat as foreign and threatening, it can trigger an allergic response.

Unlike the typical allergic reaction to shell fish or peanuts, the allergic response to AG is delayed; so, some hours after a steak dinner, for example, the allergy strikes with itching, hives, abdominal pain and — in severe cases — respiratory distress and an anaphylactic reaction. The allergic reaction can also appear after a lifetime of meat ingestion without problems. The tick apparently changes an already established tolerance, causing the immune system to attack what it previously ignored.

Once sensitized, some victims find they can no longer tolerate beef, pork, lamb — even milk or butter, which contain only very small amounts of AG. Fatty meats trigger a greater response, while grilled meats, less so because of less fat. Alcohol and exercise taken with meat can increase the allergic reaction by apparently making the gut more permeable to the sugar. Higher amounts of AG in different meats may explain differences in allergic symptom severity.

Allergic sensitization to alpha-gal has been associated with a greater risk of arterial plaques in the coronary arteries, a potential cause of heart attacks.

Tick-related meat allergy appears to be on the rise, perhaps due to changes in microbes the tick carries, making its bite more allergenic, or simply due to an increase in the number of ticks.

Mysteries remain: for example, two people can be bitten by the same tick but only one develops an allergic reaction; or a person can have allergic antibodies directed at AG but not develop a symptomatic reaction. The allergy can fade in time in some individuals.

Regardless, follow the advice I gave previously to reduce your chances for tick exposure.