Zoonotic is a word that refers to the cross-contamination of one parasite or pest on one animal host to another. Usually, this refers to the concern that bug pests that harm and infect dogs, cats and other pets can also cause harm in or on human hosts. The life cycle of some of these pests is such that it gives rise to even more serious pests, which can kill pets and make humans very sick. The following examples show two zoonotic pests, their life cycles and why they have to be eradicated professionally.
Fleas do not care what they bite and suck from, so long as it is a living, breathing blood host. The eggs that fleas lay are usually found in carpets, beds and anywhere else where a flea larvae would be very content to snuggle down and wait for dinner to come by. The common flea is so prolific that a single female can lay over 2,000 eggs in its short lifespan. You, your family, your pets and your house could be overrun with fleas within a month or two of bringing a mating pair into the house. The eggs are very difficult to destroy, so it is important that a professional pest control expert take care of this problem for you.
Dog tapeworms are zoonotic, and although a pest control specialist cannot eradicate them from your intestines or your dog's intenstines directly, he or she can break a link in the chain of their development. With dog tapeworms, fleas eat the egg sacs hanging around a dog's anus. By ingesting the egg sacs of tapeworms, the fleas themselves become the primary parasitic host of the tapeworm. Then, when a flea bites its host, it transfers the tapeworm larvae into the host, which is usually your dog or cat. If you clean up after your pet when it has a tapeworm, you may encounter a fresh batch of eggs and accidentally ingest them through improper handwashing. (You may also contract a tapeworm if an infected flea bites you.)
Ergo, if you control the primary and secondary hosts of tapeworms by killing off all the fleas, preventing a flea infestation and worming your pets often, you prevent a tapeworm infestation. Your pest control expert can help you with this indirectly, but the rest is up to you, your vet and your careful hygiene habits around pets you do not know and around your infected pets.