AUSTRALIA’S backyards and the way we use them have changed and with that change has come a rise in tick-induced allergies, such as tick anaphylaxis and mammalian meat allergy.
Associate Professor Sheryl van Nunen, a senior staff specialist at Royal North Shore Hospital in Sydney, and director of the Tick-induced Allergies Research and Awareness Centre, told MJA InSight that our love of nature has brought ticks and their saliva closer to home.
“The microclimate has changed,” Associate Professor van Nunen said, in an exclusive podcast.
“If you walked out into a Northern Beaches garden in the 1950s, you would find a paling fence, short cut grass mowed by Dad every week, a hibiscus and a lemon tree and the rest left for cricket.
“Now, we like our mulching and our overhanging trees – we love to be in nature and, in general, it’s very healthy for us. But it is tick heaven, a perfect arrangement. It’s bringing the ticks to you.”
Associate Professor van Nunen has written a Narrative Review of tick-induced allergies, published in the MJA.
Ticks can cause three types of allergies:
- a large local reaction restricted to the bite site, which looks similar to cellulitis, grows to its maximum in 24–72 hours and can last for 7–10 days;
- tick anaphylaxis, which results in the almost immediate onset of the classic symptoms of anaphylaxis and is caused by a reaction to one of five proteins found in tick saliva; and
- mammalian meat allergy, caused by a reaction to a carbohydrate moiety called a-gal (galactose-a-1,3-galactose), which is present in all meat that humans eat. Onset can be delayed 3–6 hours due to the time it takes for the a-gal to progress from the gut to the bloodstream. “Both adults and children with mammalian meat allergy after tick bites have similar findings, ranging from angioedema or gut symptoms alone through to life-threatening anaphylaxis, with severe allergic reactions being more common (65.5%),” the author wrote.
“Australia leads the world as far as tick-induced allergies are concerned,” she told MJA InSight.
“Tick anaphylaxis is an amazingly Australian problem. If you asked a German, they would tell you they don’t have it there. It has been fatal in four Australians, and I’ve seen 207 people with it since September 2011.”
In the Narrative Review, Associate Professor van Nunen wrote that:
“Estimates of mammalian meat allergy prevalence are currently 113/100 000 in the Sydney Basin, Australia, 13/100 000 in Virginia, US, and 4/100 000 in Baden-Württemberg, Germany. The locations of reports of mammalian meat allergy after tick bite in Australia correlate with the distribution of Ixodes holocyclus — around 50% of Australians are potentially exposed to bites from this species. In late 2016, a case of mammalian meat allergy was diagnosed in a man bitten by Ixodes australiensis in Western Australia, suggesting another tick species may be capable of inducing the condition in Australia. In other countries reporting cases of mammalian meat allergy, the association with exposure to ticks endemic to their regions has also been confirmed.”
“It’s a very severe allergy – 50% will have a near life-threatening reaction,” she told MJA InSight.
Unlike with bee allergies or jumper ant allergies, there is no vaccination available for tick bites, and that’s down to the way ticks inject their saliva and that saliva’s makeup.
“Bees and jumper ants have venom sacs, but ticks inject their saliva, and in that saliva [apart from the allergen] are all the infectious organisms. If you freeze-dry tick saliva you would be preserving them as well,” Associate Professor van Nunen said.
“There isn’t going to be a commercial outfit that would make an allergen extract for this. There’s no [global] market and development is [expensive].”
The good news is that tick-induced allergies are eminently preventable, said Associate Professor van Nunen.
“The condition of mammalian meat allergy, in particular, offers unprecedented opportunities for primary and secondary prevention.
“If you don’t get bitten by a tick, you won’t get the allergy. So, the first step is to stop the ticks.
“If your backyard has ticks, dress for the occasion – long-sleeved shirt, a long tail on that shirt so you can tuck it into your pants, long pants that you can tuck into your socks, and everything light coloured so that you can see the ticks.
“If you can, wear clothes that have been treated with a tickicide and get your backyard treated, particularly if you’ve been bitten before.”
Once a tick has latched on, caution is required, she said.
“The most important thing is, don’t scratch anything you can’t see. If you do have a tick, don’t disturb it because [if you do], it’ll squirt allergen into you.
“Kill the tick [using an ether-containing freezing agent] because then it can’t squirt. Wait for it to drop off if you’re not good with using fine-tip forceps or go to someone who you know is good with them.
“If you have already had tick anaphylaxis, do not touch the tick. Call 000 immediately and be transported to the closest emergency department. Do not disturb the tick until you are [somewhere you can be treated safely and quickly]. Kill the tick where it is and get their best operator to get it out once its dead.”
For GPs, diagnosing mammalian meat allergy could be problematic, Associate Professor van Nunen said, but the first step was awareness.
“First, you’ve got to be aware that the diagnosis exists. Ten years ago, when I suggested it, I was laughed at, but what I tell practitioners these days is that ticks can bite humans, then it’s likely that mammalian meat allergy will occur in some individuals.
“Taking a history is essential … [what was their last meal? Do they know if they’ve been bitten by a tick? How often have they been bitten by a tick? Has anyone else in the family had a similar problem?] … It’s an unusual allergy, very sensitive to cofactors or what I call amplifying factors … exercise, alcohol, the degree of cooking of the meat can also be a factor.
“It’s not an easy diagnosis to be sure of a lot of the time.”
Testing for the a-gal antibody will confirm a red meat allergy, and the patient’s history will confirm the presence of a prior tick bite.
“Mammalian meat allergy is what happens when an accomplished parasite such as a tick forsakes a cute furry animal such as a bandicoot, or a not so cute furry animal such as Rattus rattus, and bites a human,” Associate Professor van Nunen said.
“It is very intriguing. Between 20 million and 28 million years ago, almost all hominoids on the planet were wiped out by an infection, an epidemiological event.
“The ones that survived – humans, great apes and Old World monkeys – were the ones who had turned off the enzyme that makes a-gal … enabling the immune system to see [the infection].
“It’s quite ironic that we survived [by killing] the bugs because we don’t have a-gal … only to find that in the 2000s, people are having very serious allergic reactions when they eat meat because they can’t handle the bugs that come with the meat.”
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