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Ticked off

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Associate Professor Kevin Broady, from the University of Technology Sydney, explains the link between ticks and a growing problem for humans: red meat allergy.
Ticks are arachnids, just like spiders and scorpions, but these eight-legged creatures are much smaller. Ticks are more of a problem these days with an increasing number of allergies to adult tick bites. Recently there has been an association discovered between tick bites and the development of an allergy to red meat.
Dr Sheryl van Nunen, an allergist, had a number of patients coming from Sydney’s north shore to the Royal North Shore Hospital. In 2007, she was able to show that in almost all cases the patients had tick bites before developing an allergy to red meat. The link to red meat and ticks seemed unusual but was borne out by another discovery in the southern part of America, There, cancer patients who were undergoing a particular treatment with a monoclonal antibody called cetuximab were having anaphylactic reactions to the drug. Such strong allergic reactions were not happening in the northern parts of America, ticks being the link to these reactions.

The Australian paralysis tick, Ixodes holocyclus attached to a human host (image from Kevin Broady).
This led to the identification of the particular part of the cetuximab molecule that was causing the reactions, in this case a sugar that was bound to the monoclonal antibody protein. This allergen is now known as alphagal, an abbreviation of galactose-alpha1,3-galactose, two galactose sugar molecules with a specific linkage between them.
In Australia tick bites are inducing an allergic reaction to that sugar, a sugar that occurs on mammalian meat, but not on bird meat or fish meat. Alphagal is present on all mammalian proteins up to the higher primates. Reactions are not immediate and varied, taking up to 12 hours to manifest as stomach cramps, hives or anaphylactic shock.

There are hotspots (northern beaches of Sydney, Canberra, Lismore) where ticks are heavily endemic. Allergic reactions in these areas are as significant as peanut allergy,
Dr van Nunen has over 600 patients on her books and seeing new patients at a rate of two a week.
She has discovered that it is the way that ticks are removed that is crucial to preventing severe allergic reactions.
People who use tweezers or forceps to yank them off or those that use chemical solutions, annoy the ticks, causing extra allergen material to be injected, causing reactions. The best way to remove the ticks is to freeze them in situ with an ether-containing spray until they are dead. The ticks can then be pulled off, avoiding any injection of allergen material.
Once a person has become allergic to red meat, avoidance is the main treatment and that includes avoiding red meat as well as the ticks. White meat from chickens, ducks or fish is fine. It is not just red meat that needs to be avoided but also meat products, such as gelatin, as the work of the Canberra-based allergist Ray Mullins has shown. Gelatin is found in many products like processed food products and lollies but it is also present in many medical products where it is used as a filler in some pills. It is also used in a blood substitute products
and would induce an anaphylactic reaction if given to someone with the allergy. Doctors are now being alerted to test patients for red meat before giving them treatments containing gelatin or other medical products derived from mammals.
There is no treatment for red meat allergy apart from avoidance and in Australia, the evidence seems to indicate that the allergy will persist for a long time, possibly for more than ten years.
This contrasts with the situation in America where it appears that the allergy may diminish after two years of avoidance. The difference maybe the different species of tick causing the allergy in the two countries.
In America, attempts are being made to reduce tick numbers using non-lethal traps to exposure the native tick host, deer mouse, to pesticides which kill the ticks.
In Australia the native host is the bandicoot and to date no attempt has been made to reduce tick numbers in these populations. Ticks are parasites and while many parasites don’t kill their hosts, the most well known
Australian tick is the paralysis tick, Ixodes holocyclus because it produces a neurotoxin which is responsible for the death of thousands of pet and livestock animals each year along the east coast.
They generally do not affect native animals that are constantly exposed to them as they become immune to the neurotoxin but they can be a problem for native animals like bats and koalas when they venture into low-lying grass areas. Animals affected by tick paralysis are treated with anti-tick serum which is an antibody preparation produced from immune dogs. Research to develop a vaccine against tick paralysis is still on going.

People who work in the bush, like council workers or bush regenerators for instance, need to be educated to clothe themselves in such a way to reduce exposure to ticks and to use tropical strength spray repellents on those clothes.
Ticks latch on to the legs before travelling up to the host’s neckline, so preventative clothing is better than cure.
Doctors in tick endemic areas also need to be educated to recognise the early symptoms of red meat and tick allergy.
The group TiARA (Tick-induced Allergy Research and Awareness) has lots of information on its website (http://www.tiara.org.au) as part of its aim to educate as many people as possible.
People with the allergy are understandably ticked off.

Associate Professor Kevin Broady was interviewed by Ruby Vincent for A Question of Balance. Summary text by Victor Barry, February 2015.

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