redmeat_allergy

tick-induced mammalian red meat allergy (MMA)

Introduction

  • some people develop a food allergy with potential anaphylaxis some months after a tick bite
  • the allergy is to a sugar, galactose-α-1,3-galactose (α-gal), which is found in mammalian red meat other than Old World monkeys, apes and humans
  • it is thought that 1-20% of the population have been sensitized and has at least low levels of α-gal antibodies
  • the allergic reaction however, is delayed 3-8 hours after eating the red meat as the sugar needs to be released from the meat during digestion
  • 60% of those with MMA develop severe allergic reactions which could be life threatening
  • 10% of people who develop MMA also develop allergy to gelatin or dairy products creating a serious dietary management issue
  • Australia has the highest prevalence of MMA in the world which is presumably related to bites from the paralysis tick (Ixodes holocyclus)
  • in the USA, the allergy most often occurs in the central and southern regions, which corresponds to the distribution of the lone star tick
  • recent research also suggests that people with α-gal antibodies appear to have increased levels of arterial plaques and thus may be at risk of atherosclerosis

Risk factors

  • it seems likely that the sensitization is most likely to occur if the tick regurgitates its stomach contents back into the skin and if this contains other species blood from a previous feed
  • this is most likely to occur if the tick is disturbed or agitated during attempted tick removal
  • it seems that those who then develop an itchy lesion > 50mm in diameter which lasts for several days are most at risk

Clinical features

  • symptoms commence 3-6hrs after eating mammalian meat or immediate-onset after IV administration of substance containing alpha-gal
  • stomach pain
  • pruritis
  • urticaria
  • wheezing or SOB
  • hypotension
  • angioedema throat or tongue

Mx of acute allergy

Diagnosis of MMA

  • referral to allergy specialist
    • blood tests to detect α-gal antibodies
    • skin and basophil activation tests with cetuximab are the most sensitive, but high costs limit their use

Mx of MMA

  • there are no desensitization preventative measures available other than avoidance of alpha-gal
    • mammalian red meat
    • alpha-gal is also present in:
      • the anticancer drug cetuximab
      • intravenous fluid replacements Gelofusine and Haemaccel
      • blood thinners derived from porcine intestine
      • porcine replacement heart valves
  • carry epinephrine self-injector in case of anaphylaxis

Prognosis

  • in some people, the alpha-gal allergy may recede over time, as long as the person is not bitten by another tick
  • the recovery period can take 8 months to 5 years
redmeat_allergy.txt · Last modified: 2019/03/16 13:37 by wh