A brown, eight-legged creature, about a quarter inch in size, might make you want to skip out on your next cheeseburger.
Found in North Carolina, the Midwest and Southern US, the lone star tick can transmit alpha-gal, a sugar present in all mammals except humans, into the blood through its bite. This causes some to become allergic to mammalian meat. These ticks will be on the prowl for their next host in the coming weeks.
“The allergy can cause recurrent abdominal pains, diarrhoea, and vomiting, in addition to more obvious allergic symptoms like rash or swelling,” explained Sarah McGill, MD, an associate professor in the Division of Gastroenterology and Hepatology at the UNC School of Medicine.
McGill has been studying Alpha-gal syndrome for over eight years. Along with UNC colleagues Scott Commins, MD, PhD, and Michael Croglio, MD, McGill was one of the first to describe the condition in gastroenterology patients. McGill has now published a national clinical practice update in the journal Clinical Gastroenterology and Hepatology of the American Gastroenterological Association.
“We want the update to raise awareness,” said McGill. “When a patient has symptoms such as abdominal pain, diarrhoea, nausea, vomiting, which admittedly are very nonspecific, among the things we want people to think about is an alpha-gal syndrome,”
In addition to common symptoms, the reaction doesn’t occur until hours after someone consumes meat, making it difficult to pinpoint the exact cause. To make matters worse, there can be months in between a person getting bit by the tick and when they first begin feeling sick after a meal.
“When I was first diagnosing patients with Alpha-gal syndrome, it wasn’t in the GI literature at all,” recalled McGill. “So, these patients would come in and they’d have frequent abdominal pain and diarrhoea – symptoms of irritable bowel syndrome – or recurrent nausea and vomiting. None of my patients associated their symptoms with meat.”
Among the patients observed in a study, 75% recalled a tick bite. However, the lone star tick can bite in the larval stage when it is only 0.5 mm to 1 mm long. McGill recommends that symptomatic patients undergo a blood test called Alpha-gal IgE and, if positive, start an alpha-gal elimination diet. Among patients with GI manifestations of the allergy, symptoms should resolve or significantly improve on the elimination diet.
The alpha-gal sugar is present in mammalian meat and any products made from mammals, such as lard, milk, and butter. People with the alpha-gal syndrome should avoid eating or drinking these foods. However, tolerance varies.
“Most people do fine with dairy,” said McGill. “On the other hand, I have had some patients who have reacted to even small amounts of mammalian byproducts in processed foods. I suspect the variability in tolerance has to do with your gut microbes at some level.”
The lone star tick is most active between April and September. It is advised that patients who already have alpha-gal avoid additional tick bites because this may worsen the allergy. If a patient has symptoms like rashes, problems breathing, or swelling of the face they should be referred to an allergist. Reactions may also decrease with time and repeat alpha-gal IgE testing could be helpful in determining a future treatment plan.
“It’s important to get the word out,” said McGill. “There’s so much GI illness without a clear cause found. GI doctors should consider this as a possible problem when seeing patients with these symptoms.”