Shots stop allergic reactions to venom

For some people living in Australia, jack jumper ants (Myrmecia pilosula) are no picnic. Nearly 3 percent of people in the state of Tasmania, for example, are allergic to the stings of these ants. Such reactions can be fatal if not treated promptly.

Scientists have now successfully tested a venom-based therapy against the allergy. It’s the first so-called desensitization therapy to use ant venom, says Simon G.A. Brown of the Royal Hobart Hospital in Tasmania.

In desensitization therapy, a person receives injections of small amounts of an allergen. Physicians have used venom from bees and some other insects to desensitize people to those stings, but such therapy for ant stings has depended on extracts of whole ant bodies and has been only partially effective, says Brown.

He and his colleagues gave 20 or more injections of pure ant venom over several months to 23 healthy volunteers with the venom allergy, while 29 others with the same allergy received an inert substance. A week after the last shot, all the volunteers came back to the hospital where doctors allowed an ant to sting them twice.

Dangerous systemic allergic reactions, such as dropping blood pressure, occurred in 21 of the 29 people who had received the inert shots, whereas none of the 23 desensitized volunteers had a reaction, the scientists report in the March 22 Lancet.

The new study “is the first to show that effective immunotherapy can be provided for ant-sting allergy,” says Brown.

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