Worm Infection in Dogs and Cats


Dogs and cats are the victims of several intestinal parasites referred to as “worms.”  The most common are roundworms, hookworms, whipworms and tapeworms.  Of these four only roundworms and tapeworms are commonly seen in the stool.

At the Manchester Animal Hospital, we recommend pets be checked for intestinal parasites twice a year as worms found in dogs and cats are potential health hazards for humans too.  

If hookworm larvae penetrate the skin they can cause a condition called cutaneous larval migrans, where a potentially serious scarring and inflammation results.  Ascarid (roundworm) eggs, if ingested, can cause a disease called visceral larval migrans where tiny worm larvae migrate through the person's intestinal wall and into the body tissues.  They then grow to larger size almost anywhere in the body.  

Ocular disease is a common sequel to visceral larval migrans.  Children are at most serious risk especially if play behavior is in an environment where dog, cat, or raccoon feces may be present... such as in a sandbox.  A single adult Toxicara canis female can shed up to 100,000 eggs a day which pass into the dog (or cat's) environment with the stool. 

Often you will be able to tell if your dog or cat has worms by the symptoms they are exhibiting.  Most worm infestations cause any or all of these symptoms:  diarrhea, perhaps with blood, weight loss, lethargy, general poor appearance and vomiting, perhaps with worms in the vomit.  

Some infestations cause few or no symptoms; in fact, some worm eggs or larvae can be dormant in the pet'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 can assume different sizes and be visible in the feces.  With Tapeworms, all you might see in the stool or attached to the fur near the anus would be the small segments that detach from the end of the tapeworm. Hookworms and whipworms are so small they seldom are seen in the stool.  I recommend a stool sample and fecal analysis every six months in order to discover which parasite is present.  The presence of these worms' eggs can often only be detected microscopically, and the sample is sent to a laboratory in order to detect these parasites microscopically.

Roundworms |  A percentage of puppies and kittens are born with microscopically small roundworm larvae in their tissues.  The larvae are introduced to the developing pup in the mother's uterus—via migration through the mother's tissues.  Roundworm 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 to live in the small intestine of the pup or kitten.  The eggs that the adult worms pass in the stool can now reinfest the animal 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, microscopic in size are coughed up, swallowed, and grow up to adults in the small intestine.  Female roundworms can produce 200,000 eggs in just one day.  These eggs are protected by a hard shell, which enables them to exist in soil for up to years.  Puppies and kittens with active roundworms in the intestines often have a pot-bellied appearance and poor growth.  The worms may be seen in vomit or stool.  If not treated in time, a severe infestation can cause death by intestinal blockage.

Roundworms don't just affect young pups or kittens; they can also infest 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 can also because of illness in older dogs, be often demonstrated as poor stamina, lack of feed efficiency and weight loss.   Other signs include bloody diarrhea, anemia, and progressive weakness.  Diagnosis is made by examining the feces for eggs under a microscope.

Tapeworms|  The tapeworm is transmitted to dogs (and cats) that ingest fleas or 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. 

Tapeworms can reach four to six inches in length within the intestine.  Each tapeworm may have as many as 90 segments, though it is the last segments in the chain that are released from the worm that can be seen in the stool or attached to the fur under the pet's tail. 

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 move around a bit shortly after they are passed and before they dry up and look like little grains of rice or confetti.  It is these segments of the tapeworm which contain the eggs.  Tapeworms cannot be killed by the typical generic, over-the-counter wormers.  See a veterinarian for a treatment that works.

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 several stool samples may not reveal the presence of whipworms.   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.

Early diagnosis for the presence and type of an intestinal parasite is vital.  To do this we send the sample to a diagnostic lab where the stool (only about a teaspoonful is needed) is mixed with a special solution, which makes the microscopic eggs more visible.  At the Manchester Animal Hospital, we include the stool check on a biannual visit.  Tapeworm eggs do not show up well in routine fecal analyses so tell your veterinarian if you spot these rice-like segments in the stool or caught in the fur under the tail.

A dewormer can be used to rid your pet of worms.  The type of dewormer will depend on the type of worm present.  Not all worms respond to the same treatment and no single wormer works against all kinds of parasites.  Additionally, some non-prescription wormers are quite ineffective in removing worms from the dog or cat.   Your veterinarian will have the best kinds of wormers available for the particular type of parasite your pet has.

Prevention is critical, so remove feces from your yard or litter box at least once a week. It is also important you watch where your dog goes in the neighborhood dog park; these are often infested with intestinal worm larvae.  Use the correct wormer under veterinary supervision and have your dog or cat's feces checked frequently in persistent cases.  Do not mix wormers and do not use any wormer if your pet is currently taking any other medication, including heartworm preventative, without consulting the veterinarian. In the case of persistent reinfestations, some veterinarians will prescribe worming treatments on a routine basis all year long.

Generally, prescription wormers will be safer and more effective than over-the-counter worm medications.  Please take the worming advice of your veterinarian seriously and adhere to strict sanitation principles whenever pets and children are in close contact.

Dr. Lamb is the Veterinarian at the Manchester Animal Hospital.