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My name is***** and I would like to assist with your concern today. Although he received the flea treatment at PetSmart, I would recommend putting the Seresto collar back on. It can take up to three months to kill all fleas in all life cycles especially with flea baths. The Seresto collar will continue to kill any fleas that hatch from eggs on his body. The collar will also kill any that land on him from the environment such as the home and outside. Because he had fleas on his body, they will also be living in the environment so those need to be treated as well. Vacuuming does a great job as does washing any bedding he is around in hot water. Also, the flea bites can continue to be irritating even after the fleas have died. Dogs bite and scratch and create secondary infections due to flea bites so sometimes a short course of a steroid or an antibiotic is needed. Unfortunately we cannot prescribe medication through this site though. Over the counter you can find a topical spray to use to relieve some of the itching and irritation though.
Please let me know when you return and what questions I can answer further for you.