Internal Parasites
Internal parasites commonly infect pet dogs and cats. Some of these parasites can cause serious problems for pets—even death. Some can be transmitted to humans. (zoonosis) In spite of these dangers, most internal parasites can be easily controlled or prevented.
A veterinarian can examine your pet for parasites. A fecal exam checks for microscopic parasite eggs or protozoan parasites. A heartworm test is a blood test that checks for infective heartworm microfilaria and/or antigens shed by adult female heartworms.
The most commonly seen internal parasites of the large and small intestine of dogs and cats are roundworms, hookworms, tapeworms, and whipworms.
Other GI parasites include stomach worms,intestinal thread worms, coccidia, and Giardia. Heartworm disease is, unfortunately also quite common.
Heartworms inhabit the lungs, heart, and blood vessels of dogs and cats.
Urinary parasites are uncommon.
1. Should my dog or cat have a fecal exam? What will it tell me?
2. Should puppies and kittens be “dewormed” even if a fecal exam is negative?
3. What is deworming?
4. I got a dewormer at the store. That will take care of everything, right?
5. When should my dog be tested for heartworms?
1. Puppies can be born with worms.
2. Worms can kill a puppy.
3. Adult dogs don’t get worms.
4. Dogs give pinworms to children.
5. If a dog is on heartworm pills he can still get other kinds of worms.
Stomach – Stomach worms spend much of their adult life in the stomach of their dog or cat hosts. They can cause recurring bouts of vomiting which can include blood and mucous.
Small Intestine – Several parasites spend most of their life cycle in the small intestines of dogs and cats. Tapeworms, hookworms,and roundwormsare most commonly seen. These parasites can cause diarrhea, episodes of vomiting, a pot-bellied appearance, and general poor health. Intestinal threadworms are less commonly seen, but can cause diarrhea which may be severe.
Large Intestine – Whipworms, coccidia, and Giardialive in the large intestines of pets. Cats do not usually become infected with whipworms. These parasites can cause diarrhea which may contain mucous, or blood (coccidia or whipworms). Affected pets may appear unthrifty and lose weight.
Liver– Platynosomum is an uncommon type of fluke known to infect the bile ducts of cats. Infections are usually limited to wet tropical and subtropical areas. Snails and later lizards or toads are intermediate hosts. Cats become infected when they prey upon lizards or toads. These parasites cause general poor health and can sometimes obstruct bile ducts.
Migrating parasites
In young puppies roundworms often migrate through the lungs as part of their life cycle. This can cause lung damage as the parasites move through lung tissue. It is possible for young puppies and kittens to develop pneumonia as a result of such migration although milder respiratory problems are more common.
Dirofilaria immitis, the canine and feline heartworm, spends most of its adult life in the arteries of the lungs. It can cause coughing, exercise intolerance, shortness of breath, vomiting, or even sudden death, especially in cats.
True lungworms are uncommon parasites of dogs and cats. Cats are sometimes infected with Aelurostrongylus abstrusus, the feline lungworm. This parasite can cause coughing or sometimes trigger difficult breathing.
Capillaria aerophila is a type of lungworm which can infect both dogs and cats. It can cause coughing
Paragonimus kellicotti, the canine lung fluke can affect the lungs of dogs, especially those with access to wet areas where they might catch and eat crayfish, one of the lung fluke’s intermediate hosts.
Heartworms may be found in the heart of dogs and cats, although they tend to be found more commonly in the blood vessels of the lungs. They are more often found in the heart when there are high numbers of worms. They can block blood flow and cause death.
These parasites can cause coughing, exercise intolerance, shortness of breath, vomiting, or even sudden death, especially in cats.
A heartworm antigen blood test can be used in dogs to check for the presence of heartworms. The test is less reliable in cats because cats usually have fewer adult heartworms at any given time.
Heartworm prevention is recommended for all pets in parts of the country where heartworm disease is a problem.
Uncommon to rare parasites of the kidneys and bladder include Dioctophyma renale, the giant kidney worm, and Capillaria plicata. The giant kidney worm actually consumes the kidney it infects, eventually causing signs of renal obstruction or renal failure. Dogs and even more rarely, cats, become infected by eating infected fish or crayfish. Capillaria spp. infecting the urinary tract are thought to cause few if any problems for their hosts. Occasionally, cystitis-inflammation of the bladder—has been reported.
A zoonosis is an infection or infestation that naturally affects both humans and other animals. Roundworms and Hookworms are known to be zoonotic parasites which can be transmitted to human beings as well as other animals. Roundworms are most commonly transmitted to children who consume soil that is infected with roundworm eggs from feces. In humans, these larva can migrate through tissues, causing abdominal pain, diarrhea, wheezing, coughing, and possible fatalities from invasion of the brain or heart muscle. The eye can also be affected. Echinococcus, a relatively rare species of tapeworm can also affect human beings. Toxoplasma gondii, a protozoan parasite of cats, can have very serious effects.
Hand-washing after handling pets, cleaning up and properly disposing of pet feces, and keeping pets properly de-wormed are all sensible measures to take in preventing spread of zoonotic parasites to humans. Specific measures are recommended for avoiding the spread of Toxoplasma gondii to pregnant women.
Physaloptera rara, Physaloptera praeputialis, and Physaloptera felidis are three species of stomach worm known to inhabit the stomachs of dogs and cats. The worms are usually about 2cm in length, resemble small roundworms, and may sometimes be found in vomit from infected pets.
These parasites penetrate the mucosa lining the stomach and ingest blood from their host. This causes inflammation, pain, and bouts of vomiting. The vomit may be tinged with blood. Eggs from this parasite leave the host in feces or vomit.
Crickets and cockroaches serve as intermediate hosts for stomach worms. Frogs, mice, and rattlesnakes have been reported as paratenic “carrier” hosts. A dog or cat becomes infected when it eats an infected intermediate host or paratenic host.
There are several types of tapeworm which infect dogs and cats. Dipylidium caninum is probably the most common tapeworm. It is usually discovered when a pet owner or veterinarian notices a short (¼ to ½ inch) flattened rice or linguini -like worm segment in feces or on the fur near a dog or cat’s anus. Dried segments look like grains of rice and sometimes may be found in a pet’s bed or favorite chair.
A dog or cat becomes infected with this type of tapeworm by eating an infected flea. Fleas, intermediate hosts for Dipylidium caninum, become infected by eating microscopic eggs from inside the short, flattened worm segments passed in feces. Another type of tapeworm, Taenia spp. infects dogs or cats when they eat a mouse or similar intermediate host. These types of tapeworms usually do not cause much harm to a pet, although they do compete for nutrients from his or her food.
Echinococcus spp. are very small, dangerous, and thankfully relatively uncommon, tapeworms which complete part of their life cycle in the small intestine of dog or cats. Dogs or cats become infected from eating raw meat from an intermediate host such as a sheep or goat. The sheep or goat became infected from eating eggs that were passed in the feces of an infected dog or cat. These parasites form cysts in the tissues of the intermediate hosts or possibly humans who contact feces from infected dogs or cats and then inadvertently swallow the eggs. (Yet another reason for washing your hands before eating.)
Hookworms feed on blood and tissue fluids from a dog or cat’s intestine. One species of hookworm, Ancylostoma caninum is a voracious blood feeder which can cause anemia and even death in puppies and sometimes kittens.
These worms can infect a puppy or kitten before or shortly after birth by migrating through the placenta or through mammary glands and into milk.
Infected animals may have dark or bloody diarrhea, grow poorly, be extremely thin, weak, dehydrated, and have pale mucous membranes.
Worm eggs are passed in feces. Larvae hatch from the eggs in the environment and can infect a “new” dog or cat either by penetrating its skin or by being eaten. Humans can become infected with hookworms similarly— by accidentally eating microscopic larvae or by skin penetration. (This is one reason why some beaches do not allow dogs.) Skin penetration can cause dermatitis in the area of penetration.
Toxocara canis, Toxascaris leonine, and Toxocara cati are three species of roundworms which live in the small intestine of dogs or cats. Affected puppies and kittens may be pot-bellied, have a dull haircoat, stunted growth, diarrhea, or episodes of vomiting. Large masses of worms have the potential to block the intestines of young puppies, cause intussusception, or perforation of the intestine—any of which may cause death.
Puppies and kittens can be born with round worms or become infected very shortly after birth when infective larvae migrate across the placenta (usually seen in puppies) or into milk through the mammary glands (a more common source of infection in kittens.) Infective larvae may migrate through the lungs and other tissues.
Dogs and cats can also be infected by eating infective eggs from feces or by eating another animal such as a mouse or rat that is infected. Roundworms can also infect people who accidentally eat infective eggs. Larvae migrating through tissues in humans can cause severe problems. Visceral larval migrans, neurologic larval migrans, ocular larval migrans, are terms used to describe aberrant migration of roundworms through the soft tissues, brain and spinal cord, and eye.
Coccidia are protozoan parasites of cats and dogs. Some types of protozoan parasites (Isospora, Cryptosporidium, Giardia) live mainly in the intestines of their hosts and can cause diarrhea, vomiting, lethargy, weight loss, and dehydration. Other protozoan parasites such as Toxoplasma gondii and Neospora canis, can cause disease in other parts of the body.
Infection with coccidia usually does not cause illness in healthy animals. Animals that are inclined to become ill are those that also have other diseases or are malnourished; are kept in overcrowded, high stress conditions; or are immunosuppressed for some reason. It is more often seen in young puppies and kittens whose immune systems may not be fully developed.
A microscopic examination of fresh feces is used to tell if an animal is infected with coccidia. Special techniques are needed to find the oocysts of Cryptosporidium.
Whipworms are common parasites of the large intestines of dogs. They are thin worms which imbed their mouth ends into the mucosal lining of the large intestines. They feed on tissue fluids and blood.
Eggs from adult whipworms pass with feces. They are not always seen during fecal exams because eggs are not shed regularly. A dog becomes infected with whipworms by eating eggs in contaminated soil. The eggs tend to persist in soil. Re-infection of dewormed animals is possible, so repeated treatment for whipworms may be necessary.
These parasites can cause bloody diarrhea, weight loss, anemia and dehydration.
Aelurostrongylus abstrusus, the feline lungworm, can infect cats when they catch and eat birds that are infected. Birds become infected when they eat snails or slugs which have eaten larvae passed in feces from an infected cat. Larvae get into the feces of cats by migrating up the trachea from the lungs, being coughed up and then swallowed.
Frequently Asked Questions Answers
It is a good idea for all puppies and kittens to have a fecal exam along with their first and/or second vaccination visit. Ideally, adult animals should be checked for parasites every 6 months.
When performing a fecal exam, a veterinarian or veterinary technician uses a microscope to examine your pet’s stool for parasites or parasite eggs. Identification of eggs or parasites helps with preparing a specific treatment plan to eliminate the specific parasite infecting your pet.
Sometimes, a fecal exam does not reveal parasites that are actually present. Parasite eggs may not be seen if the parasites themselves do not happen to be shedding eggs at the particular time the fecal sample is collected. Sometimes a very small sample will not contain enough material for eggs to be seen.
2. Should puppies and kittens be “dewormed” even if a fecal exam is negative?
Because a fecal exam may miss parasites that are present, and because parasites are particularly dangerous to young animals, it is a good idea for all puppies and kittens to be treated for common internal parasites even if a fecal exam is “negative”.
Preventative deworming also helps decrease the potential for parasites to be spread to humans. Since all “dewormers” do not treat all parasites, a fecal exam is still helpful in determining what type of parasite problem exists and what type of treatment is needed.
3. What is deworming?
“Deworming” is treating an animal with medications which kill internal parasites. Some medications are more effective than others on different types of parasites. The weight and age of your pet are also important considerations in determining type and dose of medication. A veterinarian is best qualified to determine which treatments are best suited for solving a specific parasite problem for a particular pet.
4. I got a dewormer at the store. That will take care of everything, right?
Again, not all deworming medications treat all types of internal parasites.
5. When should my dog be tested for heartworms?
While most veterinarians recommend doing a fecal exam for intestinal parasites when a puppy or kitten first comes in for vaccinations, a heartworm test is usually not done until a pet reaches at least 6 months of age. It takes at least 6 months for adult female heartworms to shed the antigen detected by a heartworm antigen test. Heartworm antigen tests have not been shown to be reliable in cats.
Many veterinarians recommend placing a puppy on a monthly schedule of heartworm prevention and then testing the dog when it returns for annual vaccination the following year.
Click here for more information about Heartworm Disease.
True/False Answers
1. Puppies can be born with worms.
True. Puppies can be infected with internal parasites prior to birth. Some species of Roundworms (Toxicara Canis) have an unusual variation of their life cycle that allows larvae to lie dormant in the tissues until a female dog nears the end of her pregnancy. The larvae then migrate to the unborn puppies within the uterus. This is called trans-placental migration. Roundworms can also be transmitted to very young puppies and kittens when they nurse from infected mothers.
Hookworms can also be passed across the placenta to unborn puppies but trans-mammary transmission to nursing puppies is more common. Hookworm larvae can also penetrate the skin and infect neonates by this route. Transplacental transmission of canine heartworm microfilaria has been reported.
2. Worms can kill a puppy.
True. Hookworms can kill puppies and kittens by causing severe blood-loss anemia. Puppies can die as soon as 3 weeks after infection. Roundworms can also cause death in puppies and kittens as early as two to three weeks after birth.
3. Adult dogs don’t get worms.
False. Adult dogs and cats can be infected with the same parasites found in puppies and kittens. Adult animals do tend to be somewhat better at fighting parasitic infections because their immune systems tend to be better developed, but they can be infected and suffer poor health none-the-less. Infected adult dogs and cats also serve as a source of infection for other animals and in some cases, people. Dogs which die from heartworm disease are usually adults. Back to True/False Challenge
4. Dogs can give pinworms to children.
False. Enterobius vermicularis, The pinworm of human beings is contagious between people, but does not affect dogs and cats. Dogs and cats do NOT transmit this parasite to people.
5. If a dog is on heartworm pills he can still get other kinds of worms.
True. But, most medications used for heartworm prevention do help prevent infection with other types of internal parasites such as roundworms, hookworms, and in some cases, whipworms. Using a heartworm preventative which has activity against parasites that have been a problem for your pet or pets in the past is likely to help with overall parasite control.
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