Wildlife immune to itch from poison ivy

        As I watched a white-tailed deer with budding antlers feeding on the leaves of shrubs and plants at the edge of my yard last month, I realized that for many long moments its face was right in the middle of a patch of poison ivy. It may have even eaten some.
        And a week before, while horseback riding along a road in Middletown, the horse reached down to nibble on some roadside vegetation and dragged its muzzle through a mass of the same shiny, three-leaved, rash-producing vine.
        Just thinking of it made me shiver, since I was terribly allergic to the nasty plant when I was a kid.

I even went through a series of 10 weekly injections when I was about 12 to reduce my susceptibility. It seemed to work, as I’ve contracted poison ivy very seldom since then. But it hasn’t stopped me from being hyper-aware of it everywhere I go.
        Observing that deer and horse, however, got me wondering why they weren’t concerned about the poison ivy. Wouldn’t they get the same nasty rash as I do whenever I come near it?
        Apparently not, as I soon learned. It turns out that only primates get an itchy rash from poison ivy, and not even every primate species does so. Some aren’t bothered by it at all. Reptiles, amphibians, insects and other mammals can’t get it either. Nor can birds, many of which eat the berries the plant produces each fall.
        And don’t worry about your dog or cat. Their coat protects their skin from the active ingredient in poison ivy – urushiol – though they can transmit that oily compound to you if they get it on their fur and then you pet them. So if you know they’ve been in a patch of poison ivy, give them a bath.
        According to the Smithsonian, poison ivy is in the same family as mangoes, cashews and pistachios, strangely enough, all of which produce urushiol. Beware: If you chew on mango skin, you could get a blister rash on your lips. While you can safely eat mango flesh without any negative effects, every part of the poison ivy plant – the leaves, stems and roots – are poisonous. And if you burn it and accidentally inhale the smoke, it could have serious repercussions on your lungs and even lead to death.
        But only if you’re a primate. The rest of the world’s species – except guinea pigs, for some reason – can just treat it like any other harmless plant.
        Why that’s the case has only recently been discovered. In humans, urushiol causes what scientists call a cell-mediated immune response, which essentially means that it tricks your immune system into thinking that your skin cells are foreign objects that must be eradicated. The rash isn’t caused by the poison ivy but by your immune system attacking your own skin cells.
        Most non-primates don’t produce the skin protein called CD1a that triggers the allergic reaction when it comes into contact with poison ivy. That’s also why scientists have had such a hard time studying many skin disorders – they try to conduct experimental tests on animals, and animals don’t respond because they don’t produce CD1a.
        Some scientists think that urushiol evolved as an antimicrobial defense agent to protect the poison ivy plant against infection. It’s not a defense against people. Nonetheless, I still take it personally whenever poison ivy raises an itchy rash. I’m certain that it’s out to get me.

This article first appeared in the Newport Daily News on August 10, 2020.