Dogs fall prey to both external and internal parasites. Fleas and ticks on the outside and a variety of worms on the inside can compromise health on their own and spread secondary disease. Keeping your Yorkshire terrier parasite-free is part of good health maintenance.

External Parasites

Flea and tick prevention and eradication has gotten much simpler in recent years. You used to have to fog the yard, bathe and dip the dog, and bomb the house — each of those procedures using chemicals — repeatedly during flea season. Now, thanks to the newer products, you can give the dog a monthly pill or use a spot-on preventive without having to worry about hazardous chemicals. What will work best for you depends on your area of the country and your lifestyle. Consult your veterinarian for a choice of products. Also, note that some preventives are active against fleas only, while some work against fleas and ticks, and some also claim to repel mosquitoes.

Internal Parasites

Dogs can be infested with a variety of internal parasites, all called worms. Most of these worms, including roundworm, hookworm, tapeworm, and whipworm, occupy the digestive tract. They cause internal bleeding, diarrhea, and a dull-looking coat because they leach nutrients away from the dog. Routine examination of stool samples can identify worms, and deworming medications can combat them.

Heartworms are an even more serious threat, as they actually live and grow in the dog's heart. Good preventives exist, but once the dog has a heartworm, treatment becomes difficult. A dog should be tested for heartworm before being given a heartworm preventive. Dogs already suffering an infestation can be further sickened by the preventive.

Some canine worms can be transmitted to humans. This should not cause you undue alarm, as it's a rather rare occurrence. But it should provide additional motivation to see to your dog's good health.