I'm not sure what the shot is you're referring to, but you most likely will have to treat all your pets. Either Revolution, or Advantage, or if it's available in Canada, Capstar (? think that's right) works well. All are available through vets offices, and are the safest for pets. The first two are topical, and you apply it between the shoulder blades where they can't lick it. Capstar is a daily pill that will eventually break the flea life cycle, and is very safe. It's a good idea to find a pet friendly spray for the house, that will kill off eggs lodged in crevices. The black stuff you are seeing is not eggs, but flea dung. Eggs look like salt, but oval shaped when you look with a magnifier. YICK! Use a flea comb on everyone in your house...especailly the back area just above the tail, and cheeks. Fleas seek out the moisture from animals mouths, and back ends..YUCK! I'm curious about this shot you're talking about. Any shot that lasts six months would have me running in the other direction!