So what was he coming in contact with? Dr. Marsella said the rash was consistent in character with that caused by plants in the Commelinaceae family. Her Italian accent, coupled with the challenging pronunciation of the full botanical name (genus and species), made it difficult for me to understand what she was saying. “Does it have a common name?” I asked.
“‘Wandering Jew,’” she said. We knew this plant as an invasive exotic that many people have in their ornamental gardens. But, since we make an effort to maintain native plants, this was not one that we had growing on our 10 acres of land. “Well, we don’t have any of that,” I said, disappointed that we had reached another dead end. My husband, however, made the connection between the botanical family name and the genus of “Wandering Jew.” He asked if she had said Tradescantia fluminensis.
“Yes, that’s it.”
And then it all fell into place. We are surrounded by acres of Tradescantia — not the invasive T. fluminensis, but the beautiful Florida native species, T. ohiensis, commonly called “spiderwort” or “blue jacket.” There was still a disconnect for the medical team because most plants in the Commelinaceae family are ground creepers. But the Tradescantia that grows abundantly on our property gets as high as 36 inches, which accounted for the reaction on Max’s torso.
“Do you live nearby? Can you get some of that Tradescantia and come back with it and Max?” Dr. Marsella asked. Of course, we said. Later that afternoon, the veterinary team made a slurry from the plant and coated shaved areas of healthy skin on Max’s flank and one of his ears with the paste. They added two control spots as well. To be sure he could not paw the test areas on his side, the students made him a spectacular outfit from pink vet wrap decorated with little red hearts.
The next day, we returned to the clinic and were told that the test was absolutely conclusive. Max had developed the same rashlike pustules that we had come to expect on his underside. And once the vet team saw field photos of the plant, they understood why this dog, with his 20-inch leg length, had extensive rashes in his armpits and groin and not just on his feet, where he would have come in contact with the creeping T. fluminensis, T. pallida, and T. zebrina. The rash between Max’s toes was tame compared to those on his underside because, as Dr. Marsella explained, fur prevents direct contact with the skin.
Just as with people who are allergic to poison ivy or oak, the culprit is a chemical, in this case calcium oxalate, a compound with a microscopic crystalline structure. The irritating needlelike formations penetrate the skin, causing an inflammatory response in animals that are sensitive to them. There is no cure for the rash and no vaccine to prevent reaction. The rash almost always leads to secondary infections, which is why most dogs (and cats) that have this allergy are treated with steroids and antibiotics. Fortunately, Dr. Marsella was the lead author of a study published in Veterinary Dermatology (volume 8, issue 2) by the team of veterinarians that pioneered the use of pentoxifylline (Trental®) to mitigate reaction to calcium oxalates when used prior to exposure. The only other treatment is avoidance. Max is now on this medication 24/7, which initially worried me because it is a vasodilator and in the caffeine class of drugs. Recently, though, a friend who is a pharmacist likened Max’s dose to a person drinking a daily cup of Earl Grey tea, and I calmed down a bit. Pentoxifylline lasts about eight hours in a dog’s system, and because it can irritate the stomach, we administer it day, eight hours apart (morning and late afternoon), so it is in his system and “on duty” during the times he is most active outside.