The best news about ticks is that most bites from the arachnid parasites cause no more than minor discomfort for humans. For an unlucky few, however, a tick might be the origin of an allergic reaction, which in some cases could be severe.
Now, a peer-reviewed study led by the Garvan Institute of Medical Research, in Sydney, has shed further light on how bites from some tick species can lead to dangerous allergic reactions in humans.
The study found an overrepresentation of the 3-7 antibody in the blood of patients with mammalian-meat allergy (MMA).
This antibody neatly binds to a sugar molecule called galactose-α-1,3-galactose (usually shortened to α-gal), which humans and other higher primates are incapable of producing.
The sugar can be introduced to humans through bites from species like the Australian paralysis tick (Ixodes holocyclus).
In extreme cases, the allergic reaction caused by the body’s α-gal immune response could cause restricted breathing or anaphylaxis, requiring immediate medical attention.
But an ongoing consequence can be the development of allergies to mammalian meat and other products, such as gelatine and milk.
North Sydney reports more mammalian-meat allergy than anywhere on the planet
New South Wales – particularly around Sydney’s northern beaches – is the world’s MMA hotspot, with more than 1800 cases reported in the region.
The link between tick bites and the allergy was discovered in 2007 by Australian specialist Professor Sheryl van Nunen, a co-author of the Garvan research published today in the journal PNAS.
Van Nunen discovered the connection while working at the Northern Beaches Hospital, near Manly in northern Sydney, when dozens of patients reported allergic reactions to red meat.
She says things haven’t changed much in the last 15 years: “There isn’t a week go by that I wouldn’t see two people with this allergy.”
I. holocyclus ranges along Australia’s east coast from as far north as Queensland’s Daintree region down to Lakes Entrance, in Victoria’s East Gippsland area, and has been reported in Tasmania.
Not so sweet: human immune system evolved to target α-gal
Not everyone who suffers a tick bite will develop anaphylaxis, nor is MMA guaranteed.
Factors like the number of tick bites, the volume of injected tick saliva and a person’s own genetic makeup are all factors than can determine a severe reaction or ongoing allergy.
The study’s authors suspect humans evolved-out the ability to produce α-gal, to instead protect against infectious diseases.
That’s a view consistent with recent studies into the presence of α-gal on the surface of malaria-inducing Plasmodium parasite, which have found the human immune system’s response to the presence of α-gal coating the parasite can swiftly destroy the organism.
“We have more than 70 types of antibodies and this one [the 3-7 antibody] is significantly overrepresented with α-gal recognition,” says the study’s lead author Professor Daniel Christ, Garvan’s head of antibody therapeutics and director of the Centre for Targeted Therapy.
“We seem to be genetically predisposed to being sensitive to this sugar.”
Tick off: tick removal is a case of freeze, not squeeze
Not so long ago, the simple household remedy for tick removal was to use a pair of tweezers – but the simple squeezing of these tiny terrors can cause more harm than good.
Agitating a tick by force risks the injection of more of its potent, anticoagulant saliva into the body. It may even burrow deeper into the skin.
Instead, the Australian health department only recommends the use of freezing agents containing ether (such as over-the-counter wart removal sprays) to remove adult ticks. The Tick Induced Allergies Research and Awareness group (TIARA) also suggests the use of permethrin cream to kill small tick larvae and nymphs.
Preventative measures include the use of long-sleeved permethrin-treated clothing, DEET-based insect repellents and regular checks for ticks on the neck and scalp for those living in regions where ticks occur.
Homes can also be tick-proofed through moisture reduction, fencing to restrict animals (bandicoots are well-known tick carriers), treatments for pets and tick-specific insecticide use around the house.
Matthew Agius is a science writer for Cosmos Magazine.
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