The link is the flea tapeworm (Dipylidium caninum). This worm lives in the dog’s gut, and when mature, starts shedding egg-filled body segments via the dog’s anus.
The eggs are eaten by flea larvae living in the dog’s bedding, carpets etc. The larvae then pupate, and when the adult fleas emerge, they are already infected with the immature stage of the tapeworm.
When your dog is bitten by an infected flea, it reacts quite naturally, by scratching, licking and biting – and as a result, often swallows the flea.
By this circuitous route, the tapeworm finds a new host – or re-infects the same one – and the cycle begins all over again.
To eliminate this particular worm, it is not enough to treat your dog. If you also have a flea problem, you must deal with this too, or the dog is certain to be re-infected.
Drontal will tackle the worms, but you should also ask your vet about effective flea control that treats both your pet and its surroundings.
The eggs are eaten by flea larvae living in the dog’s bedding, carpets etc. The larvae then pupate, and when the adult fleas emerge, they are already infected with the immature stage of the tapeworm. 
