Olive leaf extract is antiviral , antifungal, antiparasitic, and antibacterial. I would buy a pound of it and mix it (maybe a 1/2 to 1 teaspoon) with the dogs food. I would also keep the dog on it for a long time, certainly past the point of recovery. There are a few other natural antiparasitics but olive leaf is one of the best and has many other benefits. It shouldn't be hard to find olive leaf in Spain (olive oil capital?).