Ticks That Make You Sick: Ixodida-Induced Vegetarianism

Greetings fellow parasitophiles! I'm sorry that I've been out of the loop for so long. I have a million excuses for not writing...teaching, book publishing, revising to two different manuscripts for scientific publication, traveling to another country to work on an excavation site, moving into a new home, preparing for the fall semester...but none of these are good ones. As you can probably tell, life's been more than a little crazy for me this summer! All of my lame excuses aside, today I'm jumping back on the horse to blog about parasites. Let's start with something most of us have had to deal with at some point...ticks.

Between field work, camping, hiking, and lots of other types of outdoor activities, most people have encountered these little ectoparasites. These menacing little creatures strike fear, disgust, and anger into the hearts of all those who enjoy the great outdoors. A great variety of species exist, but only a handful carry diseases that we have to worry about. Rocky Mountain Spotted Fever, Lyme Disease, Ehrlichiosis, and others are problematic here in the states. It would be easy to pick one of these diseases to discuss at great length here on Parasitophilia, but I have something a little different in mind for today. Today, we won't talk about an infectious disease at all. Today, we will discuss something else that can come from being bitten by ticks....something I never thought could be associated with ticks...an acquired food allergy...to red meat.

I only just heard of this acquired allergy within the last few weeks, but the research goes back several years. The oldest paper that I could find on the subject (doing only a quick search, not an in-depth one) was published in 2009. This paper described 25 patients in New South Wales who developed allergies to red meat after suffering from reactions to local tick bites. The authors suggested what may have been the first documented association between tick bites and food sensitivities.

Fast-forward to a year ago (2013). A paper was released describing an oligosaccharide known as galactose-alpha-1,3-galactose (here-after referred to as "alpha-gal") having a connection to red meat allergy. You see, alpha-gal is only produced by non-primate mammals and by New World monkeys. Humans, other primates, and Old World monkeys produce an IgG antibody that works against alpha-gal. Alpha-gal is produced heavily in animals with lots of red meat...such as bovines, sheep, and pigs. The allergic response to red meat experienced by patients with red meat allergies is mediated, like most other allergic responses, by IgE.

The Lone Star Tick

There is strong evidence to support the involvement of various arthropods in the development of red meat allergies, however, the mechanisms have yet to be completely worked out and at this point causation has not been fully established between red meat allergy development and tick bites. So far, scientists have been able to establish that IgE antibodies to alpha-gal are specific to regions where tick bites are common problems. In particular, epidemiological evidence has focused around Amblyomma americanum, the lone star tick. Researchers have also found correlations between IgE antibodies that are specific for both proteins from ticks and for alpha-gal. This means that humans may be producing alpha-gal IgE in response to tick bites, which may, in turn, be associated with red meat allergic responses.

Another paper published this year (2014) describes a case of a patient suffering from problems for 4 years who was finally diagnosed with a red meat allergy based on IgE Ab alpha-gal titers. This study, along with previous studies from both the US and Europe strongly support the notion that tick bites have the potential to alter our immune systems in such a way as to elicit anaphylactic responses after the ingestion of red meat.

Interestingly, ticks aren't the only arthropods demonstrated to cause changes in alpha-gal antibody production. It appears that people with Chagas' disease and with Leishmania also have significant increases in serum titers of these antibodies. Both of these diseases are vectored by arthropods (kissing bugs and sandflies respectively).

As with many immunological studies, the answers to the questions how and why are far from straightforward. Much work is yet to be conducted regarding the relationship between ticks, alpha-gal, IgE, and red meat allergies. With enough time and effort, perhaps we will be able to elucidate the intricacies of these interactions so that people afflicted by these allergies will be able to eat red meat once more. In the meantime, we will continue to study this bizarre reaction and attempt to better understand its origins so that we can learn how to offset its effects.