Virtually all puppies have some degree of internal parasitism, and proper treatment can have a tremendous influence on the puppy's overall health and development. In addition, some canine parasites can have serious adverse health effects on people, particularly children. We will limit ourselves to discussing intestinal parasites, but there are parasites that infect the respiratory and urinary systems as well.
Generally speaking, intestinal parasites cause problems for the host animal by interfering with absorption of nutrients, damaging the lining of the intestinal tract, and feeding on the blood and proteins of the host. An important consideration when treating parasite problems is the life cycle of the organism. Life cycles may be direct or indirect.
Direct life cycles occur when the egg or larval stage of the parasite directly infects the definitive host (usually by ingestion) and develops into the adult stage of the parasite. Parasites with indirect life cycles require an intermediate host in which the parasite egg or larva develops before being able to infect the definitive host. Diagnosis of intestinal parasitism usually involves a microscopic examination of a stool sample. There are 4 commonly encountered "worms" that parasitize dogs.
1) Roundworms- Also called ascarids, there are 2 different species. They are extremely common in puppies, less so in adult dogs. Adult roundworms can reach 6 inches in length, and resemble pieces of cooked spaghetti. They live within the small intestine and can cause vomiting and diarrhea. Adult worms will occasionally be passed in stool. Heavy infections can cause a puppy to have a "potbellied" appearance, and in severe cases intestinal obstruction is possible.
Many puppies have roundworms at birth or shortly after, due to the fact that infective roundworm larva in the female can be transmitted to the pups via the placenta before birth, or through the milk during nursing. Roundworms represent a significant public health concern, especially for children. Accidental ingestion of infective roundworm eggs by a child can lead to aberrant migration of the larvae through the eye (ocular larval migrans) and internal organs (visceral larval migrans). Routine dewormings and timely removal of puppies' fecal material are the key to preventing roundworm associated problems.
2) Hookworms- There are several species. Hookworms are small intestine parasites that bite the intestinal lining and feed aggressively on blood. Heavy infestations can cause life threatening blood loss anemias, especially in young animals. The life cycle is direct, infection can be through ingestion of eggs or penetration of the host animal's skin by infective hookworm larvae. Larvae can also penetrate human skin, causing a skin eruption termed cutaneous larval migrans. Hookworms are commonly seen in puppies, and are more frequently encountered in adults than are roundworms.
3) Whipworms- There is one species. Whipworms are small, thread-like parasites of the large intestine. They are a frequent cause of diarrhea in adult dogs. The life cycle is direct. Whipworm eggs are thick-shelled, and very resistant to adverse environmental conditions. This means that they tend to persist in an animal's environment, and re-infection is likely.
4) Tapeworms- There are several species. The life cycles are generally indirect. The tapeworm Dipylidium caninum utilizes fleas as an intermediate host. Other tapeworm species utilize rodents and other small animals. The larval forms of the Echinococcus genus of tapeworms can infect humans, this condition is termed hydatid disease.
There are also protozoan parasites of the intestinal tract, the most significant being coccidia and giardia. These single celled organisms can cause significant disease in young animals. Giardia is also a significant public health concern.
The treatment and prevention of these intestinal parasites should be discussed with your family veterinarian, please follow his/her recommendations. In general, we deworm puppies 2 or 3 times during the first few months of life. The monthly heartworm preventatives discussed in a previous column also help control some intestinal parasites. By the way, take your puppy to the veterinarian to be "DE-wormed", not "wormed".