Some dogs have some reaction when using flea collars; the best course of action is to remove the flea collar (as you have done) and to wash any remaining residue off the neck area. There are many types of external parasite control, spot-on treatments are usually more effective and are tolerated well by dogs. If you notice any symptoms of breathing troubles or neurological signs, visit your Veterinarian immediately. Regards Dr Callum Turner DVM
Fleas: Detection, treatment, & prevention | Cesar's Way
If your dog has irritating flea bites, the first thing you should do is call your vet. Flea allergy dermatitis is very uncomfortable for dogs, and your vet will help control the symptoms of flea allergy dermatitis while you come up with a flea removal plan. Even if your dog does not have flea allergy dermatitis, the best way to treat flea bites is still, of course, to get rid of fleas.
What Do Flea Bites Look Like on Dogs? - American Kennel Club
Flea bites are much more obvious on humans, since we don’t have dense layers of fur. On humans, flea bites look like tiny red dots. If you have a flea bite, however, you probably won’t be worrying too much about what it looks like—you’ll be more concerned by how much it itches.
Here are some symptoms of flea bites on dogs to look for:
Puppy Fleas - Symptoms and Treatment Tips - The Spruce
Fleas are blood-sucking parasites, which means your pet can become anemic from biting fleas. Symptoms like pale gums, lethargy and/or low body temp could be a sign on anemia. Anemia is especially concerning for puppies or sickly dogs, and if it's not caught soon enough, it can lead to other medical complications and even death. In order to help your pet with anemia, you must stop fleas from biting your pet immediately. Also, make sure your pet is getting the right nutrients by giving him or her daily .Of course, cat’s fleas feel more comfortable on a cat, but they can live on a dog or even suck human blood. Thus, the species specificity of these insects is rather conventional: dog fleas can be transmitted to humans, and a human can infect a dog or a cat with fleas. Fortunately, it does not matter which kind of fleas you face, as you can kill them in the same way and all of them cause similar symptoms of fleas on dogs.