Internal parasites are extremely common and can threaten a pet's health. Certain types can also infect the pet owner and their families. Some of these parasites are worms such as roundworms, hookworms, whipworms, and tapeworms. There are also microscopic protozoa such as coccidia, toxoplasma, and giardia.

Infection can occur through an insect bite, ingesting a flea (as with tapeworms), or contact with an infected animal's stool. A pet might show symptoms that include anemia, diarrhea, vomiting, constipation, decreased appetite and weight loss. Even death could occur in young or weakened pets. Sometimes healthy, well-fed pets won't show any symptoms.

To detect internal parasites, a microscopic examination of a pet's stool is usually necessary. Only tapeworm segments (resembling small pieces of rice) might be identified with the naked eye. An owner might notice these segments in the pet's stool or clinging to the hair near the tail. It is necessary to identify the exact parasite the pet has because different parasites require different medication. Follow-up treatments might also be necessary depending on the parasite. Over-the-counter products should not be used unless the pet's parasite infection has been properly diagnosed and veterinary advice has been obtained.

A program to prevent parasite infections should include avoiding contact with fecal material and controlling fleas on the pet and in the environment. Also, the pet's stool should be brought to the veterinarian as often as requested up to 12 months of age and then at least on an annual basis thereafter.

(The writers are Dr. Steven B. Holzman, Dr. William R. Haagenson and Dr. Kathleen Tapley. They are associated with the Nassau-Suffolk Veterinary Hospital of Farmingdale).