All About Intestinal Parasites In Your Dog

hookworms are becoming resistant

Ron Hines DVM PhD

Hookworms are the most common destructive intestinal parasites of dogs -considerably more so than roundworms. It has become apparent that dog hookworms in the United States are becoming resistant to all the medications veterinarians commonly dispense to eliminate them. Like canine influenza, probably another “gift” from the greyhound racing industry. Read about that here.  Read more about hookworm resistance here

Intestinal Parasites Are The Most Common Problems Veterinarians See In Dogs

Although pets of any age and any lifestyle can carry them, intestinal parasites are a health problem primarily in young dogs, dogs whose lifestyle increases their risk of exposure, dogs living in substandard conditions and dogs with other health issues.

Dogs and their parasites have had millions of years to evolve together. During that time, they have, begrudgingly, learned to tolerate each other. There are a large number of these worms and assorted freeloaders; below, I list them – roughly in the order with which I run into them in practice.

There are dog owners who are misinformed regarding the ability of once-a-month heartworm preventative products containing ivermectin and pyrantel (e.g. Heartgard®Plus) to assure that their dog remains free of intestinal hookworms and roundworms. Although those products are effective in doing so in most cases, dogs with consistent exposure to hookworm and roundworm eggs may not be protected. The pyrantel kills adult hookworms and roundworms in your dog’s intestines at the time it takes its monthly pill. But that leave another three weeks or more that the dog is not protected from new worms that hatch from worm eggs it ingests later in the month or from immature worms that were in the pet’s body when the last pill was given. If you are frustrated that your dog’s fecals are coming up positive – even when your dog never misses a monthly heartworm dose, switch to a preventative whose active ingredients include moxidectin (e.g. Advantage Multi®). If that does not solve the problem and your dog has close contact with domestic livestock or wildlife, be sure the eggs seen in the dog’s feces were not actually from those sources. Nematode eggs from one animal look much like those from other animals.

How Will I Know If My Dog Has Worms?

Parasites are often “silent” and you will not know your pet has them. The more common intestinal parasites have adapted so well to their hosts (your dog), that they are living in balance and cause no observable health issues. But that can always change. It is when the parasites become too numerous for one reason or another that your pet’s health is affected. Because of their silent stealthy nature, our best approach is to try to keep your pets completely free of them before the balance becomes disturbed.The most common early signs of intestinal parasites in puppies are poor growth (stunting), dull hair coat, scrawniness (thin), lack of playful energy and diarrhea. Many of these puppies have bony bodies but potbellied, big tummies. Many are anemic. Puppies with parasite over-burden invariably grew up in poor sanitary conditions.The most common signs in older pets are lack luster, brittle hair coat, boniness, listlessness and diarrhea. Some of these older pets become picky eaters, in some, the opposite occurs – they are ravenous and some show no changes in appetite at all. In adult dogs with parasite problems, multiple health issues are common. This is because the poor sanitation that leads to parasite overload also increases their risk of exposure to other diseases and because their parasite burden lessens their resistance to other diseases (and vice versa).

In dogs that have adjusted better to their parasite load, the stools may be well-formed – but they are coated with mucus, secreted by their colon, in an attempt to shield their intestine from harm (mucoid stools).

Because a number of these parasites migrate through the lungs, some of these pets have a soft cough – particularly when their exposure to parasite eggs was sudden and massive. That can be mistaken for kennel cough.

How Will My Veterinarian Check For Worms In My Dog Or Puppy?

Some parasites are large enough to be seen in the dog’s stool. When owners bring those to their veterinarian, the parasites can usually be identified. This goes for tapeworms and roundworms and a few others. However, the rest of the common parasites of dogs are too small to be seen with the unaided eye. In those cases, your veterinarian will look microscopically for the parasites, their eggs or cysts in stool specimens that you bring.When parasites are in your dog in very large numbers, the veterinarian may be able to see them in a fresh suspension (“smears”) of the feces placed on a slide with some saline and examined under the microscope. That is the most rapid screening test a veterinarian can do. But fresh direct suspensions (smears) miss over half the pets that carry parasites. They are quite good at detecting giardia and other protozoa that live within the intestine in vast numbers, but they often miss hookworms, roundworms, and whipworms. The later parasites are attached to your pet’s intestinal lining. The vet is looking for their eggs, not the worms, and those eggs are passed only in numbers reflecting the number of parasite and their maturity and even then, only intermittently. Direct suspension smears are best used to pass the time with clients while a technician runs a fecal flotation specimen in their laboratory area – about 5-10 minutes. Even if the smear is positive for one parasite, there may be others found in the flotation. Multiple infections with several species of parasite is quite common in pets. There are a few parasites (strongyloides) that do not float to the top of the liquids used to concentrate them in the flotation methods. Some of those remain on the bottom of the flotation tube and can be found there, but most of those are picked up on the direct suspension or missed. Tapeworm (segments) and tapeworm eggs are rarely found mixed with feces. They pass out of your dog on the surface of the feces. So do not be surprised if your vet does not detect them even though you have. You need to specifically bring the suspicious objects in. Any time you bring in a suspected parasite, place it in a baggie with a moist paper towel using gloves. When they come to me shriveled and dried up like a mummy, it can be quite hard to firmly identify them. Many can be plumped up again with saline or distilled water – but that takes time. Fecal flotation is a way to concentrate parasite eggs and cysts on a slide to make it more likely they will be found. All techniques use a solution that causes eggs to float to the top and most other debris to sink to the bottom of the container. Sometimes the passage of time is all that is required. In other cases the process can be speeded up by centrifugation. Some commonly used flotation liquids are sodium nitrite (Fecasol®), sugar and zinc sulfate. Saturated table salt will work, but it is less efficient.

When you collect fecal specimens from your dog, always wear gloves. Keep the stool specimen chilled with an ice pack if you cannot get it to your veterinarian quickly – some parasite eggs hatch quickly and the resulting larva can be hard to find. Walk your dog on a leash that morning – don’t just look around your yard for a specimen

Are These Parasites A Serious Health Problem For My Dog Or Puppy?

A few of the common intestinal parasites of dogs do not cause health issues. Some, like roundworms and tapeworms, absorb nutrients through their skin (cuticle) and do not normally injure your pet’s intestine. Others, however, like hookworms, chew and erode the lining of your pet’s intestine. Strongyloides tunnels through the lining causing inflammation. Single-celled giardia block nutrient absorption and is thought to produce a mild toxin while coccidia enter and destroy the cells of the finger-like projections (villi) that allow nutrient absorption from your dog’s intestine. Your pet has great potential to brush off the effects of a few parasitic organisms. But when the number of these parasites is high, your pet’s health will suffer. Resulting diarrhea, gives less time for food absorption. Intestinal irritation lessens appetite and causes vomission (vomiting) and burrowing parasites cause blood loss and anemia. Intestines respond to parasite irritation by secreting mucus and by a “smoothing down” (villus atrophy) of the projections that aid in food absorption. Both these processes rob your pet of the nutrients in its diet.


Intestinal parasites are always worse when they affect young animals. The younger the puppies are when they are attacked, the worse the problem will be. That is because growing puppies have much higher nutrient needs and their inflamed intestines cannot absorb nutrients. Their ulcerated intestines also leak precious blood. Tiny bodies lack the mass and reserves to deal with crisis and their antiparasitic immune systems (mucosal immunity) are not yet developed. That immunity relies on prior exposure to those parasites at low levels. In addition, these small creatures do not move about far from their whelping area – so they are continually re-exposed to parasite eggs. Some of these parasites, like hookworms are transferred to the pups through the bitches milk (colostral transfer), and, possibly, while still in the womb (transplacental transfer) as well. Others, like roundworms, readily move from infected mothers to their babies while they are still in the womb. Many nematodes, such as hookworms and roundworms do not pass eggs immediately (their prepatent period). So just the fact that your puppy’s fecal exam was negative is no guarantee it is free of worms.

Adult Dogs

Adult dogs are more resistant to most intestinal parasites. However, when their environment is highly contaminated or their resistance is weakened, they too can become seriously ill due to parasites. Age-related resistance is greatest against roundworms and coccidia, whereas whipworms and hookworms can cause health problems at any age. Much of age-related immunity is acquired by prior exposure to these common parasites. So dogs that have not been exposed previously may react as seriously as puppies if they suddenly consume intestinal parasite eggs (ova). Many of these infections are said to be “compensated”. That is, the dog has adjusted to the parasite’s present with a natural immunity that keeps parasite numbers in check and the pet shows no marked signs of illness. You might not have noticed anything wrong because whatever signs are present came on very gradually. However, subtle signs and an unthrifty nature will probably be noticeable to your veterinarian.

A Bit More About Each Individual Intestinal Parasite:


Adult hookworms are quite small and barely visible to the naked eye. There are quite a few species of hookworm. Of the four that attack dogs, the most common one is Ancylostoma caninum – but they are all of concern. The warm, humid conditions of the southeaster United States, Southern Europe, Central and South America favor its survival. (Hookworms are born male and female)The great majority of dogs obtain hookworms through ingesting (eating) hookworm larva that have hatched on the ground from the parasite’s eggs. Dog stool can contain millions of these, thin-shelled eggs. When that stool contaminates damp, cool soil, conditions are right for their survival. Eggs must develop for a time before they become infective (2 days). When the hookworm eggs actually hatch into hookworm larva, they are capable of penetrating the pet’s intact skin and paw pads as well. It is thought that an occasional dog becomes infected by eating rodents contaminated with the eggs as well. Freezing, drying and temperatures over 113 F/45 C are said to kill hookworm eggs and larva in less than an hour. Many serious cases of hookworms in young puppies result from transmission through their mother’s milk. In young puppies, most of those worms reach the pet’s small intestine where they do severe damage. But in puppies over three months old, many of these ingested larva are trapped and dormant in the pet’s muscle and connective tissue. These, and hookworms that have not yet arrived at the intestine are why puppies and heavily infested adult dogs need more than one worming. Pregnancy seems to activate these encysted hookworm larva to move to the mother’s mammary glands and from there into its milk. So, the fact that the pup’s mother was tested negative for hookworms and received periodic worming medications is not an absolute guarantee she will not produce hookworm-infested offspring. After hookworm’s (3rd stage) larva are eaten or penetrate the skin, a complicated migration process begins, leading to adult hookworm parasites arriving in the pet’s small intestine, approximately 10-14 days later. Eggs that have hatched in the pet’s stomach or hookworm larva that have penetrated its skin or mouth burrow into the pet’s circulatory system (blood and lymph). From there, they are carried to the lungs. Once in the lungs, the larva then escape and are coughed up and re-swallowed. (a cough may be present at this time) This time around, the parasites attach to the walls of the pet’s small intestine where they feed on blood, mature, and eventually lay more eggs that repeat the cycle. They do not stay attached to one place, but move about causing tissue (mucosal) destruction and ulceration for all of their 4-24 month lifespans. Puppies and adult dogs with heavy hookworm loads can become quite ill. In young puppies, the infestation can be fatal. When pups die from hookworms, they die from the anemia caused by the feeding worms. This can occur very suddenly in very young animals – sometimes before other symptoms occur. But in most cases, the infestation causes bloody diarrhea, weakness, and vomiting of varying intensity. Severely affected pets often require hospitalization, supportive care and medications to sooth and protect their traumatized digestive system. Supplemental iron is also helpful, and, of course, a medication to kill the hookworms. In some cases, pups and debilitated adults can only be saved by blood transfusions. 

Worming medications kill only hookworms that have finished their journey to the intestine. Because the time that the parasites arrive in the intestine is staggered, a single worming is never enough. Pups should receive those medications at 6, 8 and 12 weeks of age – earlier when a particular litter is in danger.

Roundworms = Ascaridiasis, Toxocara canis, Toxascaris leonina

Roundworms and tapeworms are the largest parasites you are likely to see in your pet’s stool. If your dog is infested, the parasites often appear in your pet’s vomit as well. They are thin spaghetti-shaped critters, 3-18 cm long. When they are not surrounded by feces, they usually curl up in a spiral. Unlike hookworms, dogs become infected with roundworms by eating roundworm eggs – not larva. It is also common for puppies to become infected while still in the womb or from suckling (drinking) milk from mothers that harbor the parasites. Various varmints (rats, mice etc.) that come in contact with dog roundworm eggs, end up with these parasites encysted in their bodies and can transmit them to dogs if they are themselves consumed. Roundworm eggs are not immediately infective, they need about a week in the environment to activate. Overt (visible) disease due to roundworms is usually confined to puppies. By the time dogs have matured, they are quite resistant to these parasites. Often, owners only become aware of them when their pet vomits one up due to some unrelated digestive disturbance. Roundworm infection is probably the most common disease of puppies – more have them than do not have them. When the puppies carry many worms, their hair coat is poor and scurfy and their bodies do not grow as quickly. These large parasites thrash and move around in the pup’s intestine causing intermittent colic, diarrhea, constipation, and vomission. On rare occasion, worms are so numerous that they block the intestine. Small puppies with large numbers of roundworms have a typical pot-belly. Puppies bred in unsanitary conditions are much more likely to have these parasites in large numbers, but even puppies from the most conscientious of breeders are likely to contain a few. Roundworms have no mouth, so they do not chew and damage the puppy’s intestinal lining or cause anemia like hookworms do. But it is very common for puppies that have roundworms to have hookworms as well. Luckily, medicines that destroy one, destroy the other (except piperazine). Roundworms that hatch in your pet’s intestine do not stay there immediately. Instead, like hookworms, they migrate through the pet’s body (liver-lung migration), congregate in its lungs where they are coughed up and re-swallowed. It is on this second pass that they set up housekeeping in your dog’s small intestine. Because so many puppies have roundworms, all puppies should be wormed for them. They need several wormings to destroy all the parasites. I generally worm puppies at 2, 4, 6 and 8 weeks of age and again when they receive their last puppy vaccinations (14 wks). The medication (pyrantel pamoate) costs only pennies and is not toxic when given correctly. So use it liberally in puppies – but according to dose directions.

Adult Dogs

Adult dogs become quite resistant to roundworms. Occasionally, one worm will obstruct the flow of bile from the liver, but that problem is quite rare. Usually, the dog’s parasite load stays low due to antibodies the pet produces against the parasites. Roundworms, however, have the ability to go dormant during their liver-lung migration and form long-lived cysts in the dog’s body tissues. These are the parasites that reactivate in pregnant females and which move into puppies before birth or pass out through their milk. Roundworm eggs are extremely resistant to drying. So adult dogs are constantly being reinfected when they have exposure to soil or contaminated environments. The outer shell of these eggs is quite sticky, so they cling to their coat and foot pads and get eaten while grooming. Because the majority of roundworms in adult dogs are dormant, a negative fecal exam is no proof that they are not there. That is why many breeders periodically worm their pregnant and nursing mother dogs anyway. 

Giardia = Giardia duodenalis, G. intestinalis, G. lamblia

Next to roundworms, giardia is the most common intestinal parasite I encounter in practice. Because this parasite produces a solid age-associated immunity, one rarely sees it cause a problem in mature pets unless they have another, underlying, intestinal disease. This age-related immunity is incomplete and can be overwhelmed when pets are exposed to very high numbers of giardia. That is why a new puppy or pet in a multi-dog household often causes transient diarrhea in the other pets as well. Most common household pets, as well as humans, are susceptible to giardia – related intestinal problems. But because so many distinct subspecies of the parasite exist, we are uncertain which can move between species. Although humans, particularly children, regularly suffer from giardia-related diarrhea, the source is usually contaminated drinking or standing water or daycare facility exposure – not pets. Giardia living in your dog’s intestine are single-celled creatures (protozoa) that move about by means of long motile filaments (four pairs of flagella). This adult feeding form is called a trophozoites. It is a rather flattened organism with a broad “suction” disc on its bottom surface that holds it firm to the intestinal wall (proximal small intestine). After a period of time some of these giardia release, round up and form resistant capsules. These are the giardia cysts that pass out in the pet’s feces to infect other animals. These cysts can survive for long periods (8 wks) in cool contaminated water. Freezing, drying or strong sunlight kill them almost immediately, as do most disinfectants. When a new puppy or susceptible adult dog eats these cysts the cysts morph back into their trophozoites form which multiply rapidly and may invade and irritate the lining of the pet’s small intestine. But most pets that are exposed to giardia never show symptoms or develop diarrhea. They may, however, pass the bug on to your other pets.In dogs with diarrhea, the presence of giardia is quite easy to diagnose. Vets are likely to miss it if the stool sample is floated in standard flotation liquid. But when a drop of the stool is mixed with saline and examined under the microscope, the wriggling organisms are difficult to miss. They are much more difficult to locate in firm stool. There are veterinarians who claim to be able to identify the infectious cysts microscopically when they are present an fecal flotations; but I am not one of them. A more accurate way to diagnose giardia when diarrhea is intermittent or when giardia numbers are low is to use the Idexx Elisa Snap Test. (ref). It is also a great way to identify pets that are still shedding the organism after treatment. When giardia infection causes illness, it is an effusive (watery) diarrhea that can lead to dehydration. Intestinal inflammation that accompanies severe diarrhea can cause secondary problems such as weight loss, intestinal ulcerations and rectal prolapse – particularly in young puppies. A vaccine against giardia is available – but I do not recommend it. There are two medications that work well in controlling giardia (metronidazole, tinidazole), but most cases will clear up within a week with only good nursing care. 

Coccidia = coccidiosis

Isospora species coccidia, like giardia, are single celled organisms (protozoa) that have adapted to live within the body. In animal shelter situations, these organisms are found in up to 10% of the dogs admitted. Like most parasites, they go hand in hand with poor sanitation, crowding and stress. As dogs mature, the incidence of coccidiosis decreases significantly. Although mature dogs may shed the infective stage of the parasite (oocysts) from time to time in their stool, it almost never causes disease symptoms in these animals. There are many species of coccidia, but all are thought to be species-specific. So, they are not a threat to your health or non-canine pets. For instance, Isospora canis of dogs is not thought to affect cats and Isospora felis of cats is not a problem in dogs. These organisms invade the lining of the dog’s intestine causing inflammation and diarrhea, indistinguishable from giardia. They are only life-threatening in infant and debilitated (weakened) animals where the diarrhea can lead to serious dehydration and colic and limits their desire to nurse or feed. The parasite’s encysted stages (oocysts) are easy to see and identified microscopically in fecal flotation tests. The number of coccidia seen correlate well with the severity of symptoms the pet is experiencing. Coccidia transfer from pet to pet through fecal contamination and oral ingestion. It takes about a week before symptoms begin and about five weeks after symptoms subside for the parasites to disappear from stool specimens. But some dogs continue to shed a few parasites in their stools for long periods after recovery. Early in the diarrhea stage, stool specimens can still be negative for coccidia oocysts. Veterinarians, particularly those working with shelters, sometimes begin treatment of these pups with sulfa medications (Albon®) intuitively. Small puppies also may need intravenous or subcutaneously administered fluids as well as medications to calm and slow their intestines. TLC and supportive care for these infants is critical to their recovery.


Tapeworms are a very common intestinal parasite in dogs. They are disgusting to look at

but they rarely if ever cause health issues.

You can read more about the most common one in another article on this website here

Strongyloides = Strongyloides stercoralis = thread worms

This parasite can be a problem when dogs are kept on dirt or in very unsanitary conditions in hot, wet climates such as the US Gulf Coast States. It is a most unusual parasite in that it can live free and multiply in the environment; or it can live as a parasite. When they assume their parasitic form in dogs, the larva drill into dogs through their skin. Once in the pet, they migrate to the lungs, up through the trachea and are swallowed. During this migration, they have been known to cause pneumonia when their numbers were very large. In heavy infections (infestations), dogs develop diarrhea and weight loss, particularly if they are young. Because the parasite multiplies best at higher temperatures and mud, one sees more of it in the summer and during periods of heavy rain. Dogs with a few parasites do not develop symptoms. Some larva never do reach the intestine, encysting in the dog’s tissue before they get there. These parasites are often missed on routine fecal flotation. That is because they sink to the bottom of the container, unlike the parasite eggs that float to the surface. They can occasionally be found on direct microscopic examination of the stool. (Many veterinarians put dogs with persistent diarrhea on a 3-day fenbendazole (Panacur®) treatment even when their fecal flotations are negative. That is because fenbendazole is one of the few medications that kill strongyloides) I see it most commonly in puppy mill dogs. You can read more about strongyloides in the paragraph below that deals with parasites that can affect you as well.

Whipworms = Trichuris vulpis

Whipworms are another common parasite of dogs. Because they inhabit the lower intestine (colon and cecum), they do not cause the violent diarrhea and illness common with parasites of the small intestine. The majority of dogs that carry this parasite show no signs of illness. However, some do develop chronic lover intestinal inflammation (colitis) that causes repeated urgency to defecate. When these dogs pass stool, it is often coated with mucus and occasionally flecked with bright blood. The blood remains bright red because it originated low in the intestine, as opposed to the blood of hookworm disease that originated higher up. It is common for these dogs to take a long time pooping and for the initial stool portions to be much firmer than the last portion. Whipworms do not pass large numbers of eggs, so their presence can be missed in fecal exams. It often takes repeated fecal flotations to find them. Even when none can be found, many veterinarians faced with these typical colitis signs treat the dogs for whipworms – even when no eggs can be found. (they commonly put them on 3-6 months of a milbemycin oxime (Interceptor) heart worm preventative) Whipworm eggs are distinctive in shape and very resistant to drying. Whipworms are most common in dogs housed on dirt or on concrete runs and when dogs are kept in large groups, so the problem is associated with kennels. Whipworm eggs must remain in the soil quite some time (2-4 wks?) before they become infective to a new dog. These eggs have hard, thick shells, so they are very resistant to drying, sunshine and chemical disinfectants. They can remain infective for years. After a 2-4 week period, a larva develops in each egg. When some of these infective whipworm eggs are eaten by your pet, the larva emerge in the pet’s small intestine, later migrating farther down into its cecum and colon where they attach and begin to siphon blood. After 2-3 months, these adult parasites begin producing eggs of their own that pass out in the dog’s stools. Common over-the-counter dog wormers (pyrantel pamoate, piperazine, etc.) will not kill whipworms. The best medications are milbemycin oxime or fenbendazole. Even with these, several treatments are usually required and reinfection from contaminated environments is common. 

Cryptosporidium = C. parvum, C. felis

This coccidia-like protozoan parasite is commonly found in the intestines of dogs, cats, humans and other animals. It occasionally causes a mild, transient diarrhea. Dogs become infected through fecal contamination or through consuming fecally contaminated food or water.It’s telltale resistant cysts (sporulated oocysts) are hard to identify in the feces because they are exceedingly small. When it is suspected, it is best identified through laboratory PCR testing. It is primarily a concern when pets are living with immunocompromised owners. If it spreads from the pet to humans with weak immune systems, it can cause serious intestinal inflammation, dehydration, fever and weight loss. 

If My Dog Scoots or Licks Its Rear. Is That A Sign She Has Worms?

Worms do not cause your dog to scoot or lick its rear end. That story originated with human pinworms, which do cause serious anal itching. However, dogs that have parasites often have loose stools. As normally formed stools pass over the pet’s two anal glands, they naturally evacuate them of secretions. When your pet has persistently soft stools, these glands do not evacuate properly. That bothers your pet and causes it to scoot and lick its anal region. You can read about anal sac problems here. Persistent diarrhea also inflames the anus – compounding the problem.

Are Parasites A Concern If I Feed My Dog Raw Meat?


One of the reason humans have evolved to eat cooked meat is that it lessens exposure to disease. Parasites and bacteria are continually looking for good ways to get around and infect new hosts. Traveling through their food supply is a very effective means of getting around. Dogs and humans have evolved together over the last 14,000 years. Just like us, they do quite well when their diets are cooked. Some parasitic and bacterial diseases of dogs, particularly associated with consuming raw meat are certain tapeworms, trichinosis, echinococcus, pathogenic E. coli, toxoplasmosis, listeriosis, etc. I prefer feeding pets homemade diets because the quality of ingredients in most commercial pet foods is poor. But I suggest that the ingredients be heated well to make them safe for your pet. If you feel you must feed raw meat to your dog, feed it supermarket meat that is safe for human consumption. Many, but not all, of the larger parasites that pose a threat to your pet’s health are destroyed by freezing (20 day @ –15 C or 6 days @ -30 C). But those temperatures cannot be relied upon to kill bacteria. I do not know of any beneficial health reasons owners would want to feed meat to their dogs raw.

How Often Should Healthy Dogs Be Wormed – How Often Should Its Stool Be Checked For Parasites?

Most pet owners receive periodic reminder notices from their veterinarians that it is time to have their pet’s fecal checked for parasites. This is often done in conjunction with reminders that it is time for your pet’s yearly booster vaccinations. The typical practice model that veterinarians in the United States have followed for the last 70 years has been to derive the majority of their income from repeat, yearly services and the minority of their income from required surgical and medical procedures. Fecal examinations, yearly vaccination boosters and the sale of medications and diets provide the bulk of your veterinarians’ revenues. There will always be a rare pet that appears to the owner to be healthy but carries some form of parasite. But those cases are very few. When was the last time you had your fecal checked? Your veterinarian works with parasite eggs day in and day out. When was the last time your veterinarian had his/her fecal checked? You alone can access the specific parasite risk in your pet. That is based primarily on its lifestyle and the sanitation of its environment. But considering the poor accuracy (ref) of veterinary fecal flotation methods when parasite numbers are few or moderate, it is much safer to just keep your pet on a monthly heartworm or flea preventative that also prevents intestinal parasites. Most veterinarians send out their reminders every year; but some send them out every six months. Even if you depended on twice-a-year fecal exams, your pet could pick up a parasite egg the day after the examination. It is a bit like checking to see if your back door is locked, twice a year. Fleas and intestinal parasites also use similar methods to move from pet to pet. Pets in temperate climates that have no flea problem are considerably less likely to have intestinal parasites either. My advice is for typical household pets in the Developed World. If your pet’s lifestyle differs from that, it does not apply to your dog. Pets that routinely enter contaminated areas, pets that are routinely boarded, pets with specific idiosyncrasies (quirky eating habits), pets that live in large groups or that range over large areas, have different needs that may include routine fecal examinations and shorter vaccination intervals that I usually suggest.

Can Any Of These Parasites Infect Me Or My Children?

Yes, quite a few of them can. They often do not complete their life cycle normally when they infect humans, but they are a cause for concern. The most common human problem associated with intestinal parasites of pets are cutaneous and visceral larval migrans. This problem occurs when parasite larva penetrate human skin or when parasite eggs are accidentally consumed. When people accidentally eat dog roundworm eggs, the migrating larva that hatch from those eggs usually do not find their way to the intestine. Instead, they wander lost through body tissues, causing inflammation wherever they pass. When they wind up in the liver (visceral larva migrans) or other abdominal organs they can produce fever and inflammation that can be quite hard to diagnose. If they enter the eye (ocular larva migrans) they may damage the retina and vision. A telltale sign of this problem is often an increased blood eosinophil count. These problems are more common in children because of their less-developed immune systems, their less developed hygienic habits and the likelihood they will play in contaminated areas. (A certain roundworm of raccoons, baylisascaris, and, occasionally, of dogs is a particularly nasty one.

Children are always attracted to cute puppies – another potential source of exposure. Supervise them and wash their hands

Dog hookworms are the most common cause of cutaneous larval migrans – a rash that occurs when these parasites attempt to burrow through human skin. The symptoms are similar to those of chigger bites, but the red areas are streaky rather than round. Shady, moist and cool areas where grass has been denuded (worn away) are the most common places these larva are picked up. Giardia is a common cause of human diarrhea. Most cases result from drinking contaminated water or eating raw salads, but there is probably the potential of catching it from infected dogs as well. It is unclear whether the common strains of giardia found in dogs have the potential to cause disease in humans. But be safe : wear gloves and take simple precautions when you have contact with dog stool. Strongyloides infection is very rare in well-kept dogs. But when it is in the pet and its environment, it can jump to humans and vice versa. I find it most often in pet shop dogs that originate from large factory puppy mills – often in located in Kansas and Missouri. Many of these pet store puppies have stubborn diarrheas that do not resolve with pyrantel pamoate because that compound does not affect strongyloides and many vets miss the parasite on fecal exams. These stubborn diarrheas are sometimes misdiagnosed as a food allergy or sensitive intestine. Fenbendazole and ivermectin are the treatments of choice.

What Are The Medications Veterinarians Will Use To Rid My Dog Of Worms?

Piperazine = Hartz Once-A-Month™, etc.

This product has been on the veterinary and human market longer than any other It is effective only against roundworm and must be given several times. Piperazine will only kill roundworms that are living in the pet’s intestine. Those that are still migrating there are immune to its action. There is really no sense in giving it because dogs and cats that have roundworms often also have hookworms. And this medication has no effect on hookworms at all. Read more about that here

Pyrantel Pamoate = Nemex™, Strongid™, etc.

This is a great, safe product for removing roundworms and hookworms. It is inexpensive, and easy to administer. In the correct dose, it is safe to give to pregnant and very young animals. One dose is rarely enough to remove every parasite.

Fenbendazole = Panacur™, etc.

Fenbendazole kills many more species of parasites than pyrantel pamoate. It may be a better choice when diarrhea is suspected to be due to intestinal parasites, but the identity of those parasites remains unknown. Three consecutive days of treatment are generally required. It is labeled for dogs but frequently given to cats.

Praziquantel = Droncit™, etc.

This medication kills only tapeworms (and some rare flukes). It is extremely effective in doing so. It can be given orally or by injection. I prefer to inject it because then I am certain the pet did not spit it out or vomit it later. It should not be given to puppies under 4 weeks of age and I use it cautiously in debilitated animals of any age.

Praziquantel/pyrantel pamoate/febantel = Drontal Plus™, etc.

This combination kills a wide variety of intestinal parasites. The febantel portion is particularly effective in killing whipworms. It is not yet available for use in cats because, cats do not tolerate febantel as well as dogs. Also, the pyrantel portion of the dog tablet is too low for cats. Drontal cat tablets contain no febantel. Febantel is a metabolite (breakdown product) of fenbendazole

Epsiprantel = Cestex®

This medication, like praziquantel, is also effective against tapeworms. It appears to be equally effective (100%) as praziquantel in killing tapeworms.

Ponazuril = Marquis Paste®

Some shelters have experimented in the use of this compound in pets to treat coccidiosis. It is approved only for horses. Its chief advantage over other products is its low per-dose cost. Mass puppy producers also use it to control coccidiosis. I have no personal experience using it as it is generally used in animal shelter medicine because of its lesser cost.

Metronidazole = Flagyl®

This compound, metronidazole, is used to treat giardia.

Sulfadimethoxine = Albon®

This sulfa medication is given to control coccidiosis. I have not observed that puppies rid themselves of these parasites any faster when given this medication, but I give it as well to prevent additional intestinal complications and deal with concurrent health issues.

Ivermectin = Ivomec™, etc.

The bovine or swine formulation is given subcutaneously to dogs for a variety of parasitic problems – including gastrointestinal parasites. Its chief advantage is its low cost when purchased for livestock. It is sold in dog formulations (Heartgard®, etc.), but not at the strength at which it is effective against gastrointestinal parasites.

What About Natural, Homeopathic, Herbal And Other New Age Worm Medicines?

These medications are based on folk remedies that were thought to aid parasitized human beings. That was before people understood enough about the difference between parasite physiology and the physiology of our bodies to select compounds that killed one without injuring the other. It was a time when humans also believed in dragons, unicorns and a sun revolving around the Earth. They knew nothing about sanitation and believed that parasites miraculously appeared in the body (spontaneous generation). But there were some that did work. They relied on creating such severe diarrhea that the parasites were flushed out (for example, arecoline) or they were toxic plant compounds given in the hope that the amount necessary to kill the parasite was less than the amount able to kill the human (nicotine, tobacco, wormwood). Your traditional veterinarian has very safe compounds (vermifuges, paraciticides) today that are much better. They home in on specific weaknesses in the parasites to kill them without hurting your dog. There is very little reason to resort to these obsolete methods. At best, they will not harm your pet – but they are quite unlikely to cure your pet’s parasite problems either. The ones that cause severe diarrhea (purgatives) can cause problems of their own – such things as rectal prolapse and intestinal intussusceptions.

What Can I Do To Be Sure My Dog Never Gets Worms Again?

There are two things to be done to prevent your pet from ever having intestinal parasites again. You are safer with a combination of the two rather than either one alone.


Your dog relies on your judgment to prevent its exposure to parasites. If you have read this far, you already know that most of these parasites enter your dog through its mouth from infective eggs, cysts or larva that have exited in the stool of another infected pet. If you minimize your dog’s exposure to areas where this is likely to happen, you will minimize your its chances of contracting these parasites. So:

Do not let your dog range free unsupervised. Keep it leashed to keep it from poking its face in the stools of other dogs. Do not take your pet to areas frequented by dogs whose parasite status is unknown. Doggy parks are great places for parasites to be introduced to new pets.Hire pet sitters rather than boarding your dog at kennels or animal hospitals. Do not bring additional pets of unknown parasite status into your household until they have been wormed several times and their fecal status is negative. Remove stool promptly. Wear gloves, bag it and place it in your outside trash can. Keep your pets from chewing on objects that cannot be easily sanitized or come directly from the store.

Monthly Parasite Preventative Medications

Keep your pet on a monthly flea/tick/heartworm control product designed to also control intestinal parasites. They are all safe – with the exception of Ivermectin-containing products when given to certain breeds of dog. (read here) Read the directions on the product insert and follow them carefully. If a particular parasite is a problem, your veterinarian may suggest one of these products over another. Your local veterinarian will also make that decision based on which parasites are most common in your area and the degree of drug resistance that those parasites have attained. Here in South Texas, my favorite is selamectin unless I am concerned about whipworms, then I use a milbemycin-containing product. If you plan to breed your dog, worm it several times before breeding and again, with a pregnancy-safe product, just before whelping. (Pregnancy causes certain encysted (walled off) parasites to wander)

Cleaning Up The House And Yard

Some parasite cysts and eggs, such as hookworms and giardia do not have protective coatings. Those eggs die in a relatively short period when they are exposed to sunshine, warmth and drying. For those parasites, a good cleaning of the house and airing out are sufficient. Put all washable things through a hot-water washer-dryer cycle and let them sit for a week if possible before using them again. Fill a trash can with a 1:20 solution of household bleach and let any bleachable items, such as food and water bowels sit in it for an hour. Remove as much accumulated grime before the soaking. Vacuum rugs and throw away the vacuum cleaner bag. Mow your grass short, remove yard clutter and bring some sunlight into shaded areas. Keep your pets out of the yard for a week or two. Police up all areas where pets have defecated as best you can. If you can’t spread a layer of new sand, topsoil or mulch over the area. Other parasites, such as roundworms, whipworms and coccidia produce eggs and cysts that make them very difficult to destroy. That keeps environments contaminated for long periods – even years. They are much harder to deal with.

Common disinfectants have no effect on them, although all are killed by live steam and very toxic products such as formaldehyde. Their eggs and the grime that contains them must be physically removed. It is a lot of work, but it can be done when surfaces are smooth and washable. It is next to impossible on porous surfaces or on items that cannot be washed or heated without destroying them. It is possible to encapsulate these eggs and cysts with a new coat of paint on paintable surfaces (the same techniques used for asbestos and lead paint). Even though sunlight and warm temperature do not kill resistant eggs, like those of roundworm or whipworm immediately, they probably lessen the period of time they survive. Bleach, diluted to reasonable strength, will not kill roundworms. But it is said to remove the sticky coating that make the eggs cling to objects and make cleanup easier. Whenever working with bleach, it is much more effective if objects and surfaces are pre-cleaned of as much organic material and grime as possible. I dilute bleach 1:20 but most authorities dilute it more. When you use concentrated bleach, be sure to wear eye protection and gloves. Open windows and do not over-expose yourself to the fumes.

If your yard is unfenced, consider fencing it to keep out stray animals. If you must feed pets outside of your house, remove the food at night. Feeding birds is fine; but feeding raccoons and other wildlife in areas that your pets frequent is not a good idea.

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