Park worm is a parasitic disease caused by Spirocerca lupi. Having learned about this parasite in vet school over a decade ago, I have not heard about it until just recently, when I was in Israel for three weeks. Pet owners had their dogs on park worm prevention, not heartworm prevention (though heartworm exists in Israel, park worm is much more common/endemic).
Not many of us have to worry about this parasite as it is found mainly in very warm countries. Park worm, or Spirocerca lupi, is a worm that is transmitted to dogs and cats (wild dogs and cats included) when these animals eat a (dung) beetle. The beetles carry the larval stages of this worm, which mature after the dog or cat eats the beetle. After migrating from the stomach to the esophagus in some convoluted way, a wall of tissue granuloma forms around the worm, causing a nodule to form in the esophagus. Yes, totally gross (yet interesting: how does such a thing even evolve??). Affected animals show symptoms from weight loss, to fever, to vomiting, to regurgitation. In some cases, the granuloma is transformed into a malignant tumor, a process that is poorly understood by researchers. This is no benign disease!
In areas where the disease exists, dogs are on park worm prevention.
Endoscopic view of the esophagus of a dog with four granulomas (#1 looks like a tumor), each one containing a Spirocerca lupi worm.
Can you believe that Spirocerca lupi can cause swollen limbs, called hypertrophic osteopathy? In fact many diseases in the thorax/chest can cause this syndrome (like heartworm, park worm, and cancer, to name a few).