A recent increase in allergic reactions to consuming meat has been related to bites from lone-star ticks. The mechanism appears to be sensitization to a complex sugar in cell membranes found in most mammals, but not in people. How the tick bite primes the immune system to respond to the sugar isn’t entirely clear.
Read more about the link between ticks and meat allergy in the New York Times.
More about lone-star ticks can be found in the Merck Veterinary Manual.