A surge in tick anaphylaxis and mammalian meat allergy is expected after months of wet weather triggered a baby boom in the lethal critters.
Australians could be at increased risk of tick anaphylaxis and mammalian meat allergy presentations this summer, experts warn.
Populations of the tiny parasites are expected to boom after months of rain, and people living on the east and west coasts – about 60% of the Australian population – are most at risk.
There were four recorded deaths from tick anaphylaxis between 1997 and 2013, and there had been 144 hospitalisations in one year between 2017 and 2018.
“And that was really before the peak of tick anaphylaxis, so we may see a few more, unfortunately, with a wet autumn,” clinical professor and immunologist Sheryl van Nunen, from the University of Sydney, told the Australasian Society of Clinical Immunology and Allergy (ASCIA) conference in Sydney this month.
“I think we can be assured that the director of our emergency department … and his team will be very busy in a week or so.”
Australia has the highest prevalence of mammalian meat allergy and tick anaphylaxis worldwide, and it’s been increasing exponentially since 2013.
The link between anaphylaxis to tick bites and mammalian meat allergy was described by Professor van Nunen in a seminal paper she co-authored, published in the MJA in 2009.
Mammalian meat allergy is triggered by the mammalian sugar molecule, or oligosaccharide, alpha gal (galactose-α-1,3-galactose).
The blood-sucking arachnids sensitise their host to alpha gal by using their long hypostome to burrow into the skin and “communicate with our bloodstream directly”, the allergic diseases physician at Northern Beaches Hospital explained.
“Unfortunately, this bypasses the dendritic cells, so the immune system is forced to make a decision about what’s in the saliva of the tick. And that doesn’t work out sometimes for the human.”
“She [the female tick] constructs that blood lake and extracts everything she needs to make her 2500 to 3000 babies, puts them on a nice piece of leaf litter, dabs a bit of sunscreen on them and shoots through.”
Mammalian meat allergy usually showed itself three to six hours later, once the carbohydrate alpha gal was absorbed in the gut, Professor van Nunen said.
Twenty-nine countries now have recorded cases of mammalian meat allergy after tick bite, including the US, Germany, France, Spain, Switzerland, Sweden, the UK, Italy, Norway, Japan, South Korea, Panama, Brazil, South Africa, Ivory Coast and New Zealand.
There were very few cases of mammalian meat allergy between 1987 and 2003, but Professor van Nunen said the start of fox baiting in 2003 saw the number increase exponentially as ticks were forced to find new hosts.
Additional Australian research presented by Bronte Cross from Northern Beaches Clinical School, part of Sydney’s Macquarie University, showed that older women with non-B-group blood types living in the norther suburbs of Sydney – a leafy area where ticks are prevalent – were most likely to develop tick anaphylaxis.
The study included almost 300 people with systemic reactions to ticks, including 80 people with both tick allergy and mammalian meat allergy. Of that cohort, 60% were female, people aged 61-80 had the highest prevalence of anaphylaxis, and 75% were atopic. Non-B blood groups were the most common among those with anaphylaxis, with type A and O making up 75% of the group.
Professor van Nunen drew attention to an important public health message – patients with tick-induced mammalian meat allergies faced serious additional coronary risks.
Research by her colleagues had shown that alpha gal sensitisation was associated with increased obstructive coronary artery disease and more severe myocardial infarcts.
The incidence of unexplained coronary artery disease in the northern suburbs of Sydney increased from 11% of myocardial infarcts to 27% in the past decade in people with no cardiovascular risk factors, she said.
“Alpha gal sensitisation is independently associated with the degree of soft plaque or non-calcified plaque burden, independently associated with obstructive coronary disease, occurs at high frequency in patients who have more severe episodes of myocardial infarction than those were stable CAD, so it’s a measure of plaque instability as well,” she said.
Professor van Nunen also advised checking levels of tryptase, which were elevated in people with mastocytosis, associated with more severe allergic reactions to stings and bites.
“Have a high index of suspicion for coexisting mastocytosis in your tick anaphylaxis and mammalian meat allergic people because we’ve seen quite a few people with that,” she said.
For those affected by mammalian meat allergy, avoiding meat was not the only restriction, Professor van Nunen warned.
They also needed to avoid medications and devices that contained meat-derived products or by-products because they could cause anaphylaxis, she said.
Those products include vaccines containing gelatine, porcine heart valve prostheses, collagen implants made from bovine bone, cells savers used during spinal fusion surgery that contain gelatine, and snake antivenoms made from horse.
The cancer treatment cetuximab (Erbitux, Eli Lilly) contained alpha gal, and there were three fatal allergic reactions to the drug in Australia and eight more deaths worldwide. Cetuximab is used to treat advanced bowel cancer and head and neck cancers.
Professor van Nunen had some advice on the best and worst ways of removing ticks. The most common tick removal methods were using the fingers or scratching the tick out, which conferred the highest risk of tick anaphylaxis, followed by tweezers or forceps.
Pulling a tick off with your fingers was “the worst possible way to do it”, she said.
“Do it inappropriately, and within moments, you’re regretting that decision very much,” she said.
“Freezing it, not squeezing it is the way to go, and taking it out with fine-tipped forceps afterwards is your chance for success.”
The chance of being bitten by a tick could be reduced by 99% by “dressing for the occasion”, Professor van Nunen said: factory bonded work wear treated with the insecticide permethrin, crewneck long-sleeved t-shirts tucked into trousers, which in turn are tucked into socks.
In good news, mammalian meat allergy was not always permanent, Professor van Nunen said.
If people with tick allergies were bitten by a tick again, it increased sensitisation and “recharged the allergy”. “[But] if our patient doesn’t have a tick bite … within 12 to 18 months there’s a significant reduction in the alpha gal-specific IgE level. And within three to four years the majority can get back onto meat again, if they wish.”