Parasitic Worms in Dogs


Repeated roundworm infestation in Sheltie

Question: Dr. Micheal Richards, Our Sheltie who is 1 1/2 years old has had Roundworms so many times we keep roundworming him , and making sure he get 2 doses of Roundworm meds in a 2 week period,but nothing seems to be getting rid of these Roundworms completely.

He was dewormed 3 times as a young puppie than at 7 months old he had Roundworms so bad he was vomiting them.It was terrible our Pokie got so sick.

Out Vet gave us Drontal Plus and we used it on both our Shelties to make sure they both got rid of them.We used it twice 2 weeks apart.Although our Older Sheltie has never shown any signs of roundworms nor did we see any in his fecals.But we did see many in Pokie our youngest Sheltie. But after the 2nd Worming we saw no more.

Than about 3 months later I decided on my own to give Pokie Nemex 2 as he was coughing the same way when he had Roundworms before.Sure enough he had Roundworms again so on to the 2nd Dose again.

Than about 2 Months or so later I decided to Roundworm again because he had this little coughing spells again, again he had Roundworms , so onto another 2 doses again.

Than 2 months go by and we took 2 samples of Fresh Fecal.... twice in that day, to our Vet to check for Roundworms on Pokie again, and no sign of any Roundworms at all. 3 weeks after the Fecal exam and Pokie has a little cough again so I give him Nemex 2 again , and he has Roundworms again and it never showed up in the Fecal exam at all.

The Reason I used the Nemex 2 is because Pokie seemed to get extremely hyper on the Drontal Plus which really scared me so that is why I used Nemex 2 all this time.We bought it fresh from the Pet Store and keep in stored properly the whole time.And we had used 2 bottles now.

All this time in our whole life we have never seen any of our dogs ever get Roundworms and keep them in their system so long.As a matter of fact Pokie is the only Dog that has ever had Roundworms that we have had in 30 year.

Pokie has that same little cough again and I highly suspect Roundworms again, why is he never getting rid of these Roundworms do you know.I am so frustrated and feel terrible that our Dog has Roundworms and is never completely ever getting rid of them.And I feel like I am harming him giving him Roundworms Meds all the time.

Could he have a Liver Problem or a Bowel loop that the Worms eggs are living in? We had treated our Grass , and Entire yard and Sugar our Old Sheltie has never had a sign of roundworms ever. Out Vet suggested that we test Pokie for Heartworms and put him on Heartguard Monthly to kill Roundworms do you think this is a Solution for our Sheltie Pokie? We have no Heartworms here and never have that is why our Vet does not test for Heatworms but says we have to Test before we give Heartguard. Is they something Natural , or a Homepathic Roundwormer that is safe. I want the Best for our Dogs and Heartguard scares me because of the Ivermectin in it and I have heard that some Shelties have died from it.

Answer: Barbara-

It is unusual for a dog that is over a year of age to have persistant roundworm infestation. Roundworms can encyst in body tissues and then be stimulated to start a new migration to the digestive tract. The only medication that I know of that can help with this encysted stage is fenbendazole (Panacur Rx). I would recommend deworming with this medication several times for three days each time, or even using it continuously for a period of time. It is sometimes given to pregnant bitches from the 42nd day of pregnancy to the 14th day after the puppies are born to control roundworms that are activated during pregnancy, so it should be safe to give it this long.

Then I would recommend using one of the monthly heartworm medications to keep roundworms under control after that. Ivermectin at the dosage found in Heartgard (tm) is safe for shelties. I have searched for documented information on death from ivermectin at the heartworm prevention doses for both shelties and collies and have found no proven cases. I would be interested in knowing of any that you know for sure to be factual.

Keep an eye on Pokie for evidence of increased susceptibility to other illnesses. I am not sure that there will be a link between the inability to control roundworms and other immune system weaknesses but it seems possible.

Mike Richards, DVM 3/21/2001

Roundworms in pregnant dog and panacur safety

Question: Dear Dr. Mike, I wrote you once before about a Pembroke Welsh Corgi bitch who had been bred to a young dog with lymphoma......and the bitch missed so the issue ending up being moot.

Well, I've bred a different bitch to a different dog, and we're nearly 7 wks into a pregnancy. Looks like a large litter, will get her xrayed at around day 56 to get a count.

I was wondering what your feelings are about using panacur (fenbendazole) as described in the Merck manual for treatment during pregnancy of roundworm infestation. The dam in question is 4 yrs old and this is her first litter. She has been on Interceptor for the past three years, year round.

If you consider panacur a useful addition in a case like this, would you confirm the dosage? We have historically dosed at the rate of 1cc (liquid, labeled as Safeguard for cattle) per 4 lbs. of body weight, for 3-5 days for giardia and general deworming. The Merck manual suggests deworming pregnant bitches daily until the pups are 14 days old. Or, should we just deworm the pups later on with Nemex like most folks do, and we've done in the past?

I'll be talking to my local vets this coming week, but doubt they've had a client ask to do this before (I moved here from California, and they seemed a little more aggressive/informed out west in this type of situation).

Also, this bitch has a history of giardia but no recent outbreaks (within the past year). She was vaccinated and boostered with the new vaccine in spring '99 by the CA vet but had outbreaks after that. We used metronidazole for the giardia, but it was resistant so on the vet's advice we went to panacur which would control the outbreaks. We have noticed no outbreaks since moving east in fall of 99. This probably has no relation to this use of panacur but thought you should have the history.

Thank you, Carrie

Answer: Carrie-

Roundworms have an odd life cycle. There are dormant larvae in the tissues of most adult dogs and these can be activated around the 42nd day of the pregnancy and then migrate to the fetuses in the uterus and become active infections. Due to this, and the apparent safety of fenbendazole for use during pregnancy, some reproductive specialists advise giving fenbendazole during the the last stages of pregnancy to try to interrupt this tissue migration. Fenbendazole must be given for three days in a row to be effective and the dose is 50mg/kg per day for roundworms in dogs. The suspension from of fenbendazole (Panacur Suspension tm, Safeguard Suspension tm) are 100mg/ml, so the dose would be approximately 1ml per 4 lbs of body weight. I haven't actually seen any studies to verify that this works well but it is a good theory and should be safe to try. The recommendations in the Merck manual seem a little excessive, to me, but fenbendazole is pretty safe and it probably wouldn't cause any harm to give it from the 40th day of pregnancy to the 14th day of gestation.

I am comfortable with deworming puppies at 2 weeks of age, using pyrantel pomoate (Nemex Rx) and then every two to three weeks until they are twelve to sixteen weeks of age and deworming their mother at the same time. This seems to be sufficient to provide protection from health problems associated with the worms in the puppies but may not be as good at stopping environmental contamination as the deworming program in the Merck Manual. This is a link to the Center for Disease Control recommendations for deworming programs, for another opinion:

With the history of past problems with giardia it seems like it would be best to use fenbendazole for at least one of the early pre or post-partum dewormings in the bitch, though. Just in case she is still harboring the organism.

Mike Richards, DVM 3/10/2001

Roundworms, hookworms, whipworms and tapeworms.

Question: I have a stray here in a 6x12' pen. It was discovered she had worms yesterday and she was at the vet overnight getting medication and one more dose I will give her tomorrow. My BIG worry is that even though I picked up all of her stools and disposed of them in a plastic bag, before I knew she had the worms I walked around the pen and wonder if I have spread the larva/eggs into my yard and house where I have six dogs of my own. I have sprayed her area with 1 gal water and 1 cup bleach solution and covered the ground with a tarp as it was raining. (I hate to see what she does to it tonight!) What other precautions can I take? She gets another worm dose in three weeks but I believe I can send her back to CPA in 7 days when her shots (parvo, etc.) take effect. I am worried sick. How soon should I have my dogs checked for worms? They sometimes get tapeworms but I don't believe they are as contagious as the other types and usually get rid of the (tapeworms) easily. Thank you, Dixie PS: How long do the larva/eggs survive on the outside? Forever?

Answer: Dixie-

There are four types of intestinal worms that dogs get on a fairly regular basis. They are roundworms, hookworms, whipworms and tapeworms.

Most dogs have roundworms (Toxocara canis, cati or leonina) at some time in their life. This worm can be passed to puppies while they are in the uterus and while they are nursing. Eggs that are passed can develop into infective larvae that are capable of directly infecting another dog. The eggs may also infect an intermediate host, such as earthworms, mice, rats and moles and then when this creature is eaten by the dog develop into adult roundworms in the dog. Roundworms have a strange life cycle, migrating out of the intestine and into the lungs (and other organs) before returning to the intestines. Once infected, a dog may pass millions of worm eggs in the stool. The eggs can live for several months in the environment. They are sensitive to ultraviolet light, so pens which are exposed to direct sunlight do not support the life cycle of the worm as well as more protected pens. Roundworm eggs can be killed by using aqueous iodine solution (Clinics of North America, November 1987) but are not killed by chlorine bleach, although it is supposed to remove the sticky outer coating of the worm, making it easier to cleanse them from infected areas. If your adult dogs are on heartworm prevention medications there is a good chance that they are being dewormed with a medication that can kill roundworms on a monthly basis, which should be sufficient to prevent any real worry over them getting infected, especially since dogs become more resistant to infection with roundworms as they get older. Cleaning up stools daily prevents the spread of the eggs pretty efficiently and is a good practice to prevent infections.

Hookworms (Ancylcostoma or Uncinaria) are less common than roundworms but are still a major problem in southern areas of the U.S. (Ancyclostoma) and not too uncommon in the more northern areas (Ancyclostoma and Uncinaria). Hookworms eggs develop into infective larvae which can pass through the skin or be ingested and cause infection. The eggs and infective larvae are susceptible to sunlight and drying. There used to be a product sold that would treat infected dirt pens and kill the hookworm eggs but I have not seen it for at least ten years. The heartworm prevention medications Heartgard Plus (tm), Revolution (tm) and Interceptor (tm) kill hookworms, so dogs on these preventative medications are also being treated for hookworms monthly, which should be sufficient to prevent problems with them, as well. If you are not in a heartworm area monitoring stool samples every few months and treating if you find evidence of infection should be sufficient to prevent major problems from these worms. Cleaning up the stools daily also helps to prevent the spread of hookworms. I do not know how long hookworm larvae live in the environment, but I think they are not as hardy as roundworm eggs and larvae. There is no intermediate host to worry about, either.

Whipworms (Trichuris vulpis in dogs) has the most environmentally resistant eggs of all the worms. The eggs of this worm can live for longer than a year in the environment. They are susceptible to drying and sunlight. The Clinics of North America issue recommends treating concrete pens with a horticultural flame gun to kill the eggs, which I suppose might work on dirt, as well. This worm is killed by milbemycin, the ingredient in Interceptor (Rx) heartworm prevention but is not killed by the other monthly preventative medications. Therefore, it is more important to monitor fecal samples for evidence of the worm. The time from infection to the appearance of worm eggs in the stool is over two months, though -- so it can take awhile to know if this worm will become a problem when there is potential contamination of the soil. Whipworms are harder to kill than roundworms and hookworms (or at least fewer medications do it successfully). We use fenbendazole (Panacur Rx) for whipworm therapy but there are other medications that will work. Your vet will have one that he or she likes to use.

Tapeworms are usually acquired by eating infected fleas (Dipylidium caninum) or small rodents or rabbits (Taenia species). Good flea control eliminates most problems with tapeworms except in dogs who are allowed to run free or to hunt small animals at times.

Even though it may not be possible to rid your yard and pen of the worm eggs easily, there isn't a lot of reason to worry excessively over the worms. In many cases preventative measures are already being taken due to the use of heartworm medications and when this is not the case, checking stool samples and treating in infections and cleaning up the stools on a regular basis should be sufficient to clinically prevent significant problems with worm infestations.

Mike Richards, DVM 2/4/2001


Question: Dear Dr. Mike:

Myfriends 9 month old mixed breed has had no energy for four days, she broke out of her kennel four days ago, came back after 8 hours with a few scrapes and not acting like herself. My vet diagnosed her with whipworm and prescribed the meds for it. But I am now wondering why she is still not herself. INFO: She lets out a little whimper when she jumps off the couch. Sometimes whimpers when she is just laying still. She was spayed 1 month ago. She is up to date on all her shots. She is on Heartguard, but I am switching to Interceptor. She did have diarrhea, but not anymore. She has not puked. So, I would like to know if whipworm would cause her to not have any energy or cause her pain? Thanks

Answer: J-

It isn't too unusual for whipworms to cause a dog to feel tired or to cause diarrhea but it doesn't usually cause pain associated with things like jumping off of the couch.

It isn't too unusual for a dog that goes off on a jaunt to run hard enough to cause muscular soreness or to exacerbate a problem like hip dysplasia and make a dog lame. It also isn't too unusual for dogs that disappear for a while to suffer a traumatic event, like being hit by a car or fighting with another dog. Sometimes, it takes a day or so for an injury to show up from a traumatic event.

If she is still sore on Monday, it really would be a good idea to think about getting her rechecked by your vet, just in case there is an injury or some other problem contributing to her behavior.

It isn't unusual for an exam to show a problem that can explain all the symptoms evident at that time when there are actually other problems that don't show up or that aren't recognized because a plausible explanation is found and so more involved diagnostic tests aren't run. In these situations it is important for you to stay vigilant for futher problems, which you have done.

If she still feels under the weather tomorrow it would be a good idea to schedule a recheck with your vet.

Good luck with this.

Mike Richards, DVM 12/12/99


Q: My vet tells me my dogs- boxers- have whipworms, a heavy infestation and that Heartguard Plus will take care of the problem, but I've heard different from other breeders. I can't find anything on your website about it. Could you please give me some more info about whipworms. I've read that they are very hard to get rid of. Whipworms are not listed on the Heartguard insert.

thank you Chris

A: Chris-

Meriel (manufacturer of Heartgard) makes no claim that it will kill whipworms and I do not think that the active ingredient, pyrantel, is a good choice for whipworms, either. In this case, I think that you need to check again with your vet to make sure that he or she isn't having one of those days when a person just gest off track or to be sure that you did hear the instructions correctly. I think you do need an additional medication. Whipworms can be controlled using several safe medications, such as Panacur (Rx).

Mike Richards, DVM


Q: Hi my name is Janet. I really like your web site. It is very useful in my research for my parasite paper. However, I think you could add hookworm to your list of parasites.


A: Janet-

There are four species of hookworms that infect dogs and cats in the United States. They are Ancylostoma braziliense, Ancylostoma caninum, Ancylostoma tubaeforme and Uncinaria stenocephala. In dogs, A. caninum is the most common hookworm and causes the worst disease. In cats, A. tubaeforme is more common but is less likely to cause severe disease than A. caninum. Dogs in the Northern states and in Canada are more likely to be infected with U. stenocephala as it prefers cold climates and A. caninum prefers warm climates.

A. caninum hookworm infestation in dogs can lead to severe anemia, especially in puppies. These hookworms have big appetites and attach to the intestine and feed on the dog's blood. The other three types of hookworms are less likely to cause severe anemia but it is a potential problem with them. Signs of hookworm infection include weight loss, pale color, black or tarry looking stools, weakness, anemia and death. In areas in which hookworms are prevalent there can be skin disease in pets associated with exposure to the larval worms as well.

Hookworms can be acquired from the mother's milk, from penetration of the skin by hookworm larvae in the environment and from eating hookworm larvae. Some vets think that it may also be transmitted during pregnancy from mothers to puppies but this is controversial and I believe that it has been ruled out in cats.

One of the problems with hookworms is that they can accidentally infect humans. This creates a problem called cutaneous larva migrans, which loosely translates to worms migrating through the skin. Humans pick up the hookworm larvae from areas contaminated by dog feces and they penetrate the human's skin just like they would the dog's. Since they don't belong in the human they don't develop into adults but just migrate around in the skin, causing sores and inflammation, until they die. This is a good reason to keep dogs and cats from defecating in playground areas, beaches and other places where people's skin is likely to come in contact with the ground.

Fortunately, the monthly heartworm preventatives are also effective at controlling hookworms and can provide a measure of protection against the possibility of the cutaneous larva migrans syndrome occurring in the humans that own dogs and cats on heartworm preventative medications. In areas in which heartworms are not a problem but hookworms are, it is a good idea to consider having a pet's stool examined for the presence of worm eggs once a year and when clinical signs that may indicate infestation occur.

We will add this information to our site, too. Thanks for the suggestion!

Mike Richards, DVM

Roundworm picture

Bob from Queensland, Australia sent us a great roundworm picture. The worm was passed by his new Border Collie X puppy, Cane. Cane was adopted from the local Shelter and is 12-14 weeks old. The screw in the picture is 30mm or 1 1/4" inches long.

Roundworms and people (Zoonotic)

The roundworms most commonly associated with pets are the Toxocara and Toxascaris species of roundworm (there are many, many species of roundworms). These two species of worms are transmitted to humans through the ingestion of roundworm eggs which contain infective larvae. Typically it takes between one and three weeks for these eggs to develop from the time they are "laid" to the time they contain an infective larvae.

Dogs can acquire roundworm infections from their mothers while in the uterus. Therefore, it is important to begin to deworm dogs at 2 weeks of age. To the best of my knowledge cats are not able to transfer roundworm infections to kittens in the uterus and therefore it is usually recommended that deworming begin at about 6 weeks of age in kittens as it takes about that long for the infection to reach the stage where deworming medications are effective. Dogs should be dewormed every 2 weeks until they are about 3 months old .

There is some fear that roundworms may be passed by a puppy licking the owner. While the transmission rate through this avenue of infection is probably very very low it is still a good idea to observe good hygiene and wash hands and faces after playing with the puppy.

Once the initial infection is treated properly it is a good idea to occasionally check a stool sample for the presence of worms or to consider prophylactically administering deworming medications if the situation seems to warrant it.

Occasionally a physician will advise one of my clients to put their cat outside to reduce the risk of infection with Toxocara or toxoplasmosis. I truly believe that this advise is wrong. An indoor cat is unlikely to pick up an infection with roundworms or toxoplasmosis as there is no ready source of the worm eggs indoors. The litterpan is easily cleaned and most people don't dig around in the pan much. On the other hand, an outdoor cat is easily reinfected with roundworms from the soil and is very likely to defecate in places like gardens where people do tend to dig around a lot. If you have cats, or even if you don't, it is a good idea to wear gloves while gardening. Clean vegetables grown in the garden before eating them. For most people, these preventative measures are just normal procedures but it is good to know there is a reason for all this caution!

Roundworm infection in people can cause "flu like" syndromes, with fever, liver enlargement, changes in the white blood cell count and differential and in some cases eye damage. I do not know for certain how the diagnosis of roundworm infection in a human is made. Your physician will probably know, though. It is unlikely that you have been exposed to infective eggs but if you or a family member experience an illness it would be worthwhile to inform your physician of this possibility.

Mike Richards, DVM


Michael Richards, D.V.M. co-owns a small animal general veterinary practice in rural tidewater Virginia. Dr. Richards graduated from Iowa State University's College of Veterinary Medicine in 1979, and has been in private practice ever since. Dr. Richards has been the director of the PetCare Forum...