Let's examine each type of worm individually:

Dog and Cat Parasite Eggs As Seen Under The Microscope In A Stool Sample Analysis
Ascarid (Round Worm) Egg	Whipworm Egg	Hookworm Eggs	Tapeworm Egg Packet

Worms in dogs and cats!
Why does the veterinarian want to check a stool sample?  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 on the right 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... (See the photo below.) 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 be seen under the microscope and that's how their presence is detected...by looking for their eggs under the microscope! 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: diarrhea, 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.

Why should the veterinarian check a stool sample?
Early diagnosis for the presence and type of intestinal parasite is very important.  The stool (only about a teaspoonful is needed) is mixed with a special solution to make the microscopic eggs more visible. Depending upon which kind of worm is present a certain type of wormer may have to be used. For example, if a cat has roundworms the veterinarian will want to prescribe a certain kind of medication specific for the elimination of roundworms.  If tapeworms are present, a different wormer will be used. Not all worms respond to the same treatment and no single wormer works against all kinds of parasites.  And some non-prescription wormers are quite ineffective in removing worms from the dog or cat.  Your veterinarian will have available for you the best kinds of wormers for the particular type of parasite your pet has. Therefore, stool samples should be taken to the veterinarian for microscopic examination for the worm eggs if worms are suspected. Many veterinarians include the stool check as part of the annual health examination.

Prevention
Remove dog feces from back yards at least weekly, use the correct wormer under veterinary supervision, and have the dog's feces checked frequently in persistent cases. Do not mix wormers and do not use any wormer if your dog is currently taking any other medication, including Heartworm preventative, without consulting the veterinarian.  In persistent reinfestations, some veterinarians will prescribe worming treatments on a routine basis all year long.  Generally, prescription wormers will be safer and more effective (although often more expensive) than over-the-counter worm medications.

When walking the dog in a neighborhood or park, remove all feces so that the dog does not contribute to contamination of soil. Dogs and cats that are in generally good condition may not act threatened by worm infestations and may not even show signs of having worms. However, it's a good idea to keep your dog and cat as worm-free as possible so that if disease or stresses do occur, the pet has greater reserves and defenses to handle the crisis.

Tapeworm eggs do NOT show up well in routine fecal analyses!  Tell your veterinarian if you spot these rice-like segments in the stool or caught in the fur under the tail.

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 reinfest 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.  Not good!   NOTE:  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 anemic 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 diarrhea, weight loss, anemia, and progressive weakness. Diagnosis is made by examining the feces for eggs under a microscope.

Whipworms
This parasite is more often seen in dogs than cats.  Adult whipworms, although seldom seen in the stool, look like tiny pieces of thread with one end enlarged. They live in the cecum, the first section of the dog's large intestine. Infestations are usually difficult to prove since the whipworms shed comparatively few eggs; so an examination of even several stool samples may not reveal the presence of whipworms.  If a dog is presented with chronic weight loss and passes stool that seems to have a covering of mucous (especially the last portion of stool the dog passes), and lives in a kennel situation or an area where whipworms are prevalent, the veterinarian may prescribe a whipworm medication based upon circumstantial evidence.  Repeat wormings may be necessary especially if there is a probability that the dog will become reinfested.   Although they seldom cause a dog's death, whipworms are a real nuisance for the dog and can be a problem for the veterinarian to diagnose.

Tapeworms
Dried tapeworm segments are displayed in the images below...
Tapeworms...  Another intestinal parasite, the tapeworm, is transmitted to dogs and cats that ingest fleas (fleas think tapeworm eggs are real  tasty!) or that hunt and eat wildlife or rodents infested with tapeworms or fleas. If you were to see an entire tapeworm you would notice that they are arranged with a small head at one end and many tiny brick-like repeating segments making up the rest of the worm.  There are generally two types that infest dogs and cats; tapeworms can reach 4 to 6 inches in length within the intestine. It is the last segments in the chain that are released from the worm that can be seen in the dog or cats' stool or as in these photos, attached to the fur under the pet's tail.  An entire tapeworm may have 90 segments!  Many cases are diagnosed simply by seeing these tiny terminal segments attached to the pet's fur around the anus or under the tail; they even move around a bit shortly after they are passed and before they dry up and look like little grains of rice or confetti.  These segments of the tapeworm contain the eggs. Tapeworms cannot be killed by the typical generic,  over-the-counter wormers; see the veterinarian for prescription-only treatment that really works.  Don't waste your time or money on non-prescription tape worm medications... they don't work very well.  For a description of prescription pet wormers, browse NationalPetPharmacy.com.