Red Meat Allergies Caused by Lone Star Tick Bites
A Strange Cause of a Food Allergy
As strange as it may sound, researchers have discovered that some cases of red meat allergy are caused by a bite from an animal called the lone star tick. The animal normally lives in the southeastern United States but is gradually spreading up the east coast of North America. Its spread to a new area corresponds to an increase in the incidence of red meat allergy in that area.
Researchers have noticed that people with major allergy symptoms after lone star tick bites—such as the appearance of large, red welts—are more likely to develop a meat allergy. Blood tests have shown that the affected people are allergic to a sugar in the meat called alpha-gal. The tick bite is believed to sensitize people to the sugar.
Several thousand people in the United States are thought to have developed a red meat allergy due to a bite from a lone star tick. The number of affected people is expected to rise as the tick spreads to other parts of the country on the bodies of animals.
The Lone Star Tick
Like other ticks, the lone star tick (Amblyomma americanum) isn't an insect. Ticks are relatives of spiders and belong to the same group of animals—the class Arachnida. Insects belong to the class Insecta.
The lone star tick has a brown or red-brown body. It gets its name from the single light spot on the back of the female. This spot may be white, cream, yellow, or gold. Like a spider, the tick has eight legs. It also has appendages called pedipalps around its mouth.
The tick's body is up to a quarter of an inch long. The male is generally smaller than the female. Ticks feed on blood and look larger when they have just had a meal.
There are four stages in the tick's life cycle—the egg, larva, nymph, and adult. The egg hatches into the larva, which looks like a very tiny tick. It has only six legs, however. The larva eventually sheds its outer layer to become a slightly larger nymph, which has eight legs. The nymph finally molts to become the adult.
Since each stage of a tick's life cycle looks almost the same apart from size, its development process is known as incomplete metamorphosis. An animal such as a butterfly undergoes complete metamorphosis because the larva (the caterpillar) looks very different from the adult (the butterfly).
A Magnified View of a Living Nymph
How Do Ticks Find Humans?
Ticks are parasites that can't fly or jump. Nevertheless, they are very good at finding and attaching to their hosts. Some clues that ticks use to detect a suitable host include the heat, moisture, breath, and odours released by a human or animal. Some ticks detect vibrations created by a moving host or the shadow created by the host's body as it moves near the tick.
Ticks wait on leaves or grass near areas where suitable hosts travel, sensing their environment. Many wait with their front legs outstretched so that they can quickly climb on to a human or an animal as it passes by. This process is known as questing. Other ticks wait in a shelter until they sense that a host is approaching and then run towards the host. The lone star tick seems to use both of these strategies. It's described as being "aggressive" in its search for a victim.
A tick grabs hold of a human with the claws at the end of its legs and then searches for an attachment spot. Once it finds a good place, it cuts into the skin with sharp mouthparts. The tick then inserts a feeding tube to withdraw blood. These preparation steps take from minutes to hours. A person may not feel the tick's presence because the tick injects an anesthetic. This prevents the person from feeling pain and trying to dislodge the animal. Once a tick begins feeding, it may continue to do so for hours, days, or even weeks if it isn't removed.
A Nymph Prepares to Feed
What Is Alpha-gal?
Alpha-gal is the short name for a carbohydrate called galactose-alpha-1,3-galactose. This chemical is found in the muscles (or meat) of all mammals except primates, the order to which humans belong.
Beef, lamb, and pork come from mammals and contain alpha-gal. Meat from mammals is red in colour before being cooked and is therefore known as "red meat". Chickens, turkeys, and other poultry aren't mammals and produce white meat that doesn't contain alpha-gal. Fish don't contain alpha-gal, either.
Alpha-gal is a sugar, or carbohydrate. It's unusual for a sugar to cause a food allergy. Most food allergies are caused by proteins.
Meat Allergy Caused by Ticks
How Do Lone Star Ticks Cause Red Meat Allergies?
Lone star tick saliva is a complex mixture containing many different chemicals. When a tick bites us, some of its saliva enters our body. The mechanism by which the tick's saliva causes an alpha-gal allergy isn't certain, but the process is thought to be as follows.
When a tick bites an animal, a chemical that either is alpha-gal or closely resembles it enters the tick's gut. When the tick later bites a human, it injects saliva containing alpha-gal into the victim's bloodstream. Up until this point, the person's body may have been able to deal with alpha-gal entering the digestive tract in food. When the alpha-gal enters the blood of a sensitive person via a tick bite, however, the immune system creates antibodies to destroy the irritating chemical. Histamine is also made to help the attack. Unfortunately, the histamine produces the unpleasant symptoms of an allergy.
When a person eats red meat after being sensitized to alpha-gal, their immune system responds as though it has been exposed to the tick chemical again. It creates an even stronger attack against the alpha-gal molecules found in the meat. The overreaction of the immune system produces an allergic response.
The proposal that lone star ticks could cause red meat allergies was first suggested in 2007. In North America the link is now generally accepted and is becoming well known.
Symptoms of a Red Meat Allergy
The symptoms of an alpha-gal allergy may be severe, which is why the allergy is so worrying. The affected person may experience itching, hives, and swelling. These symptoms may be restricted in range or may be part of anaphylaxis, which is a severe allergic response that affects the whole body. Anaphylaxis may be accompanied by symptoms of anaphylactic shock, which include vomiting, diarrhea, difficulty in breathing, and a rapid and dramatic drop in blood pressure. Anaphylactic shock is a life threatening condition.
The symptoms of a red meat allergy don't appear immediately after eating the meat but are delayed for several hours. The reason for this isn't known for certain. It's been suggested that the alpha-gal is concentrated in the fatty parts of the meat, which take longer to digest than the protein component. The delay often means that it takes a while for the patient or their doctor to link the allergy symptoms with red meat ingestion.
An allergy to red meat due to the presence of alpha-gal may not be permanent. In at least some people it seems to weaken after a few years. This may not be true in every case, however.
Treatment for the Allergy
Anybody with a suspected red meat allergy should consult a doctor. People with a serious allergy are often given an epinephrine auto-injector to carry around with them. A common brand is the EpiPen. Epinephrine is a hormone that counteracts the symptoms of anaphylactic shock, including the low blood pressure and the difficulty in breathing. It also relaxes muscles in the digestive tract.
An alpha-gal sensitive person must avoid red meat (and should always have their epinephrine injector with them if it has been prescribed). Chicken, turkey, eggs, fish, shellfish, beans, and lentils don't contain alpha-gal and are a good source of protein. Vegan "meats", which are really meat substitutes made from plant material, are also available.
In some cases a sensitive person may have to avoid dairy milk too, since this also contains alpha-gal. Luckily, a range of non-dairy milks are available today for people who choose not to drink milk or who are allergic to dairy products. Some of these milks are rice, oat, almond, soy, and coconut milks. Alpha-gal is also present in some medical drugs, so it's important that all doctors seen by a patient with an alpha-gal allergy know about the disorder.
Preventing Tick Bites
Red meat allergies can develop due to other causes beside tick bites. Taking steps to avoid bites could be very helpful in preventing an allergy in some people, however. Since ticks can transmit diseases, it's a good idea for everyone to avoid them.
Some methods to help prevent the bites are described below. Ticks are small animals and can crawl through small spaces, which needs to be remembered when trying to create a barrier to prevent them from contacting the skin.
- Avoid woods and bushy areas as well as places known to have a large population of ticks.
- If you do enter a wooded area, cover your skin as much as possible. Wear long pants tucked into boots or socks. Wear a long sleeved shirt and tuck the shirt into the waistband of pants. Also consider wearing a wide brimmed hat.
- Stick to established trails instead of making your own. Don't walk through tall grass or other vegetation.
- Walk near the centre of a trail to avoid overhanging branches or plants where ticks may be waiting for victims.
- Wear light coloured clothing so that ticks can easily be seen if they get on to your body.
- Chemical prevention is somewhat controversial, but the standard recommendation for avoiding ticks with a chemical barrier is to apply DEET to exposed skin and permethrin to clothing and shoes.
- When you get home after a hike, examine your skin carefully for ticks. The sooner the animals are removed from the body, the less likely they are to transmit disease. Pay special attention to hidden areas of the body such as the armpit and the back of the knee, which is where ticks often settle.
How to Properly Remove a Tick
Removing Ticks From the Skin
If you do discover a tick attached to your skin, a pair of fine-tipped tweezers is the best tool for removing it. It's a good idea to carry the tweezers in a portable first aid kit while hiking or walking in rural areas. Fine-tipped tweezers should also be available at home, since ticks are sometimes found in gardens. The University of Manitoba video above demonstrates the proper technique for tick removal. Once the tick has been removed, the skin should be disinfected with alcohol and the area monitored.
Tick bites don't necessarily lead to disease. However, pathogens (microbes that cause disease) sometimes pass from the tick's mouth into the bite site. If unusual or unpleasant symptoms develop at the site of a tick bite or elsewhere in the body soon after the bite, a doctor should be consulted. In addition, if you develop an apparent allergy to red meat (or another food) after previously being able to eat the food, a doctor should be consulted for a diagnosis and treatment recommendations.
- Gibbens, Sarah. "A Tick Bite Could Make You Allergic to Meat—and It's Spreading." National Geographic. http://news.nationalgeographic.com/2017/06/tick-bite-meat-allergy-spreading-spd/ (accessed August 15, 2017).
- Smith, Tavia. "Allergists say alpha-gal red meat allergy better understood, as numbers continue to increase." Vanderbilt University Medical Center. https://news.vanderbilt.edu/2016/12/21/allergists-say-alpha-gal-red-meat-allergy-better-understood-as-numbers-continue-to-increase/ (accessed August 15, 2017).
- "Ticks." Centers for Disease Control and Prevention. https://www.cdc.gov/ticks/index.html (accessed August 15, 2017).
- Cuttler, Marcy. "Aggressive tick whose bite makes people allergic to meat is arriving in Canada." Canadian Broadcasting Corporation. http://www.cbc.ca/news/health/lone-star-tick-allergy-1.4215708 (accessed August 15, 2017).
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© 2014 Linda Crampton