Poison Ivy Vaccine in Development as 50 Million Americans Affected by Plant’s Poison

by Jennifer Shea
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Poison ivy may seem like a minor nuisance. But to anyone who stumbles across the plant, it can mean weeks of uncomfortable itching and pain. And together with poison oak and poison sumac, poison ivy is responsible for 10 percent of lost work time due to injury among U.S. Forest Service employees. It even causes one-third of their west coast contingent to miss work during wildfire season.

As if that weren’t enough, there is evidence that climate change is making poison ivy worse, Scientific American reports. A Duke University study found that when confronted with higher levels of carbon dioxide, poison ivy churns out a more allergenic type of urushiol, the resin that causes the rash.

But, fortunately for horticulturalists everywhere, there is a vaccine in development. It would be injected once every year or two to block the cellular reaction that causes the itching in the poison ivy reaction.

Poison Ivy Vaccine Would Help 50 Million Americans

It is estimated that poison ivy rashes afflict 10 to 50 million Americans every year. Roughly 85 percent of Americans are allergic to poison ivy, poison sumac or poison oak. About 10 to 15 percent of those suffer from extreme allergy, according to the American Skin Association.

So this vaccine would help a sizeable portion of the population. But scientists have struggled to get funding. They’ve also had a hard time gathering tissue samples from poison ivy sufferers.

Despite those obstacles, a vaccine is on the way that uses a compound known as PDC-APB. Injected into the bloodstream, the compound contains a synthetic version of urushiol’s active component. It should work to cut off the itchy reaction.   

“We believe the shot will lead to desensitization and reduce or eliminate reactions to poison ivy, oak and sumac,” Ray Hage, CEO of Hapten Sciences, which has licensed PDC-APB, explained to Scientific American.

The vaccine has worked on guinea pigs. It has passed initial safety testing in humans. Next comes the randomized controlled human trial.

Scientists Exposed Mice, Guinea Pigs to Poison Ivy Rashes

Scientists deliberately exposed mice and guinea pigs to urushiol to study how the itchy rash reaction develops. They found that there’s a certain immune chemical, IL-33, released by skin cells upon exposure. And that helps cause the itch. When IL-33 or its receptor is blocked, the mice stop scratching.

There’s a second route for poison ivy reactions. Mast cells, a part of the immune system, have been shown to trigger itch neurons in the skin.

Those two pathways are new discoveries. Scientists used to think that poison ivy itching was caused by T cells. And while T cells may cause the rash itself, the vaccine developers are betting it’s those two new routes that are responsible for the itch.

If they’re right, they could have found a lucrative solution to the poison ivy problem.

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