Dogs and cats are victims of several internal parasites frequently referred to as worms. The most common are the roundworms, hookworms, whipworms and tapeworms.  Of these four only two are commonly seen in the stool with the unaided eye...roundworms and tapeworms.  Look at the photo and you can see that roundworms can assume different sizes.  Plus when they are fresh they are whitish in appearance.  The single entire tapeworm in the photo usually will not be seen externally, and all you might see in the stool or attached to the fur would be the small segments that detach from the end of the tapeworm...  Hooks and whips are so small that they seldom are seen in the stool.  That's precisely why a stool sample is often required in order to discover which parasite is present; the eggs of all  these worms can only be seen under the microscope and that's how their presence is detected. Keep in mind that it is the goal of each parasite to stay in the safety of the intestinal tract; if they come out, they'll die!   They don't want to be detected!

Most worm infestations cause any or all of these symptoms: diarrhoea perhaps with blood; weight loss; dry hair; general poor appearance; and vomiting, perhaps with worms in the vomit. However, some infestations cause few or no symptoms; in fact some worm eggs or larvae can be dormant in the dog's body and activated only in times of stress, or in the case of roundworms and hookworms, until the later stages of pregnancy when they activate and infest the soon-to-be-born puppies and kittens.

Roundworms
A large percentage of puppies and kittens are born with microscopically small roundworm larvae in their tissues. The larvae got there via migration through the mother's tissues right into the developing pup or kitten in the mother's uterus!  The worm larvae can also be transferred to the nursing pup or kitten from the mother's milk. The larvae make their way to the intestinal tract where they can grow up to five inches in length.  They start shedding eggs and try desperately to keep house in the small intestine of the pup or kitten.  The eggs that the adult worms pass in the stool can now re-infest the same pup or kitten or other dogs and cats if somehow the egg-bearing stool is eaten.  When the worm eggs hatch, larvae  are released internally to migrate to the animal's lungs where the larvae (remember, the larvae are microscopic in size) are finally coughed up, swallowed, and finally grow up to adults in the small intestine.   So you can see that repeated exposures to egg-bearing stool or stool-contaminated soil can cause additive numbers of parasites to a dog or cat's load. If the mother has no  intestinal parasites and no encysted larvae in her tissues...the pups or kittens will be born worm free.

Roundworms are active in the intestines of puppies and kittens, often causing a pot-bellied appearance and poor growth. The worms may be seen in vomit or stool; a severe infestation can cause death by intestinal blockage. Females can produce 200 thousand eggs in a day; eggs are protected by a hard shell and can exist in the soil for years.

Roundworms can infest adult dogs and cats, too. However, as mentioned above, the larvae can encyst in body tissue of adult dogs and cats, remain dormant for periods of time, and can activate during the last stages of pregnancy to infest the puppies and kittens. Worming the mother has no effect on the encysted larvae in the body tissues and cannot prevent the worms from infecting the newborn.  Almost all wormers work only on the adult parasites IN THE INTESTINAL TRACT.

Hookworms
These are much more common in dogs than in cats. They are very small, thin worms  that fasten to the wall of the small intestine and suck blood. Dogs get hookworms  from larval migration in the uterus, from contact with the larvae in stool-contaminated soil, or from ingesting the eggs after birth. As with roundworms, the hookworm larvae can also be transferred to the nursing pup from the mother's milk.

A severe hookworm infestation can kill puppies, often making them severely anaemic from the loss of blood to the hookworms' vampire-like activities! Chronic hookworm infestation is a common cause of older dogs not performing optimally, having poor feed efficiency and weight maintenance, and having poor stamina. Often the signs include bloody diarrhoea, weight loss, anaemia, and progressive weakness. Diagnosis is made by examining the faeces for eggs under a microscope.