If you speak to a vet he or she will tell you that the most common cause of illness are parasites and pests in any sort of pet.
When a dog or a cat gets fleas it is one of the hardest things to get rid of because of the simple fact that the fleas are spread around the house aswell, they can survive in carpets of any sorts therefore curing your pet is not only enough, you will also have to cure the house. The way that this works is when fleas lay eggs they drop onto your carpet floor and then hatch and feed on the debris on the floor.
Once the Fleas have hatched they become something called pupae which are resistant to freezing, drying and insecticides and they can lay dormant for up to 6 months.
The way to prevent fleas from occurring are to give your pet a drug called lufenuron once a month, this will sterilize you cat or dog and stop the fleas from laying eggs, helping to rid the home of pests. Always get advice before applying any treatment to your pet as they may have a reaction.