Something doesn't sound right here. I've never heard of snake bite venom causing an infection with no other symptoms.A few years ago while hunting pheasants with a friend near Russell, Kansas, his pointing Lab was bitten in a front leg by a prairie rattler. The dog was treated with antibiotics for infection and after 2 weeks recuperating was back to hunting pheasants.
Treating rattlesnake venom with an antibiotic doesn't make any sense. I can see how an infection could develop from the fangs penetrating the skin the same way a would can get infected if not cleaned and treated correctly.
But what about the affects of the snake venom? How did that not have any affect? How was the antibiotic given to the dog?