Internal parasites are a subject I know WAY too much about. Why? Because they’re gross, fascinating, and affect every dog and new puppy owner. If it concerns the health of my people or my animals, you can believe I’ve done my homework.

So let’s talk parasites. Yep. That’s what I want to write about. Charming lady at parties, I must be 😂

What are the most common doggy parasites?

Roundworms

Ascarids, commonly called “roundworms”, are found in the soil pretty much everywhere on planet earth.

If you’ve ever seen dog poop with an off-white, round, spaghetti looking “worm”, then you’ve seen a roundworm.

Method of transmission is the fecal to oral route. An infected animal defecates and contaminates soil, and a hapless dog comes into contact with microscopic eggs and ingests them and presto, worms.

But puppies often get them from their mamas. They cross the placenta when a dam is pregnant (or “in whelp”) and they are also transmitted through doggy-breastmilk.

A mama can be “clear” of roundworms and totally treated before she is bred. But roundworms, like many helminth parasites, do this gross thing called “encyst”. This means that some larva (during an active infection) travel into the muscle tissue of the dog and turn into little cysts. Here they wait.

You can’t test for encysted larva in a living dog’s muscle. You just assume they’re there. Because they are. And you can’t do anything about them because there is no treatment for these parasitic sleeper cells.

Sometime during pregnancy they activate and infect mom and the puppies. This is why even in very healthy and treated mothers nearly all puppies are born with parasites and require treatment to remove them.

Gross.

Now you know.

The good news is that the species of roundworm that infects dogs almost never infects people. It can’t survive in human GI tracts and while it is possible that it can cause issues if a person comes into contact with these nasties, it is then typically only in cases of contact with super heavily infested soil (and even then it’s super rare).

Roundworms won’t hurt your dog or puppy unless they have such a crazy heavy infestation (called “a high worm burden”) that multiple parasites grow really large and clog up the puppy’s system. This is especially a concern if an infection is not treated in a timely manner and a heavy burden is then killed off too rapidly with improper medication, causing an intestinal obstruction.

Unless you have a severely neglected animal being treated for parasites without proper veterinary oversight, a roundworm infestation isn’t likely to do any harm to your baby (or your human family members).

It’s just gross.

But very easy to treat and with medication that is very, very safe.

The most common treatment for roundworms is called pyrantel pamoate. This paralyzes the parasites but it does not kill them. They detach from the intestinal lining and get passed through poop as gross, alive worms.

This is why you sometimes see worms in dog poop after they’re treated.

Here is where an intestinal obstruction can occur in a dog with an extremely high worm burden.

One medication a veterinarian may choose to use in cases of high worm burden (or in cases not responding to pyrantel pamoate) is piperazine. This removes the outer layer of the parasite that protects them from digestion and the parasites get fully or partially digested.

Yum.

Piperazine is a bit harsher on the tummy so it typically isn’t the first choice. One dose of Piperazine followed by a dose of pyrantel pamoate 24 hours later and you’ll flush out everything with less risk of intestinal obstruction in cases where this may be a concern.

The common symptom of a roundworm infection is a pot-bellied appearance (and possibly constipation or poop and/or vomitus containing visible worms).

Hookworms

Another common puppy parasite is the evil hookworm. These are very hard to test for and false negatives are common. You cannot see hookworms with the naked eye.

Hookworms attach to the lining of the gut with sharp hooked mouthparts.

They can and do kill puppies (and even adult dogs if the worm burden gets high) from anemia due to bleeding from these sharp mouthparts.

Small puppies are extremely susceptible to severe anemia from hookworm infection.

Pyrantel pamoate also removes these little bastards. It’s a good idea to treat prophylactically for hookworms once a year for all dogs. It’s easy to do and since testing is difficult and not necessarily accurate it’s safest to just give a treatment once or twice a year.

Hookworms can be zoonotic! In really tropical climates they can burrow into the soles of feet from moist soil, mud, and contaminated waterways. This is more of a 3rd world country problem, but can happen in tropical climates anywhere, like swampy parts of Florida. It doesn’t look like a pleasant experience!

Some new forms of heart worm preventatives contain the medication for hookworms in a low dose that is intended to keep such an infection in your dog at bay.

Symptoms of hookworm infection can include a dog that seems to be uncomfortable, especially if tender in the belly area, pale gums and lethargy. These are symptoms that can indicate any number of dangerous puppy infections, so they should never be ignored and a puppy should receive veterinary treatment right away if he/she is showing such signs of illness.

Whipworms

These guys tend to hang around with roundworms. They’re named for the whip-like flagella that propel them through the world. You won’t see whipworms in a dog’s poop. But if your dog is infected he will feel ill as these guys cause quite a bit of irritation when they attach to the bowel, despite their small size.

These parasites take a long time to incubate and set up shop, (typically 3 months) and as a result an infection is typically not diagnosed until the whipworm has been around for quite a while.

These guys are easy enough to treat with the over-the-counter medication called fenbendazole. However, re-treatment is necessary to be sure to rid this parasite.

Canine whipworms don’t affect humans. Woo hoo.

The symptoms of whipworm infection include large bowel diarrhea, anemia and weight loss. These guys can be really hard to diagnose as they shed eggs infrequently, and they are so hardy in the environment that reinfection is very common. Some heartworm preventatives like those containing moxidectin are an excellent way to treat and prevent whipworms and prevent the dog from being reinfected.

In any situation where reoccurring diarrhea is a problem whipworm infection should be considered, even when eggs are not present in the stool sample of the dog.

Whipworms are thankfully less prevalent today thanks to widespread use of regular deworming practices of pet owners.

Tapeworms

Everyone’s favorite parasite. Maybe you’ve even heard of the famous diet pill for humans containing tapeworm eggs? These are still common in certain countries! Alas, a tapeworm infection is unlikely to cause any weight loss in a human unless the infection is of significant proportions. So I don’t advise this method!

You may have seen a tapeworm segment in dog poop before. Long. Flat. Like a piece of white scotch tape. Totally disgusting. Totally common.

There are two common types of tapeworm that can infect a dog.

One type your dog can get from eating dead animals he finds in the yard or woods while out. Your dog also gets them fecal-oral route from any place an infected dog may have defecated.

They also encyst and travel to puppies the way roundworms do. This type is the common, doesn’t affect humans, and is easily treated with 3-5 days of the over-the-counter animal “dewormer” called fenbendazole.

The second type of tapeworm comes from a dog ingesting a flea that is carrying that particular tapeworm. Can’t get it from the flea biting the dog, but from the dog biting the flea. The dog has to eat the flea. Haha. This happens when fleas bite and your dog uses his mouth to scratch and groom himself and ingests a flea.

Keeping your dog flea free will prevent this tapeworm. This tapeworm CAN affect people. But you have to eat an infected flea. This very, very rarely happens although I have read of it happening with heavily infested animals that were sleeping in a person’s bed. Person must have eaten a flea or two in her sleep. Gross.

If your dog gets this type of tapeworm the only medicine that works is called praziquantel. The only way to tell the difference between tapeworms is via microscope.

But the presence of fleas pretty much will tell you the culprit if you see a tapeworm in a poop. It is unnecessary to treat for this type of tapeworm regularly unless you live where fleas are a huge problem and your pet is regularly infested with these parasites.

Puppies don’t get these from their mama via placenta or milk. Only from eating infected fleas. So puppies, naturally, shouldn’t be raised with flea infestations.

Fluke

These come from contaminated water sources and consuming uncooked fish. Praziquantel treats them.

Lung worm

These are a fairly uncommon nematode but can be picked up from consuming wild animals or drinking from contaminated waterways.

Symptoms include a dry, persistent cough and possible respiratory distress. Fenbendazole is a common treatment, ivermectin and moxidectin can also be used. This infection requires veterinary treatment and can take up to two months to clear up and even surgery to remove nodules in the trachea of severely infected dogs.

Heartworm

These come from an infected mosquito biting your dog. It’s not quite as big an issue as you’ve been led to believe and it’s fairly easy to treat, despite what you may have heard.

But you still don’t want to have them happen, of course.

Ivermectin is the simplest treatment and giving a monthly dose of ivermectin will not prevent heartworms (there is no actual way to prevent them via meds) but will kill off adult heartworms and prevent a heavy and dangerous infestation and over several months will cure even a heavy infestation. Ivermectin related drugs like moxidectin also work for this parasite.

The danger with treating a heavily infected animal is killing off lots of adult worms at once which can clog arteries and lungs and kill the dog.

A “slow kill” method over several months is the safest course of action. The treatment? Low doses of ivermectin. Same treatment as a “preventative”. In very heavy infestations (somewhat common in dogs from the southern USA) it might take a yr of very low dose ivermectin to cure the dog.

Typically heartworm “prevention” meds are prescribed but you can dose ivermectin at home for a lot less money if you want to do it yourself and are in a desperate spot (and trust yourself to do the math or have a veterinarian help you with the proper dosage). The safest course of action, however, is to be followed by a licensed veterinarian.

Heartworms almost never affect people but there have been a couple cases. It’s crazy rare though.

Low doses of ivermectin found in heartworm medications are very, very safe in all breeds of dog, however larger doses can be very dangerous for certain dog breeds that may carry the MDR1 mutation gene. It is helpful to have the DNA test run in at-risk breeds just to be safe. Moxidectin is a drug that has been rated as safe in dogs with this mutation, as well as properly dosed low-dose ivermectin.

Prevention of mosquito bites also help reduce the risk of infection, as well. If mosquitoes are unavoidable the topical Advantix II helps significantly to repel mosquitoes from biting and some temporary natural repellants are helpful as well, though you must be careful when using essential oil products on dogs.

Protozoa

Ew. My least favorite. Protozoan infections are EVIL. Ugh. I hate them. And we have likely all encountered them.

Coccidia (2 main types. Isospora and cryptosporidium) and giardia.

These guys are practically impossible to eradicate from the environment, they’re very hard to treat, they are ubiquitous (meaning freaking everywhere) and really, really, REALLY annoying.

Crypto is the only one that bothers people (of the canine variety, that is. Humans get coccidia and giardia, only we get a human specific type). Crypto typically only affects those humans with compromised immune systems. But is a legitimate concern for those people. Fortunately, the genus isospora is more common.

Giardia is typically treated with metronidazole (Flagyl) which is an antibiotic that doesn’t kill giardia but stops it from reproducing. A 10 day course of fenbenzadole works better and these two medications can work great together.

Coccidia is best prevented with toltrazuril but in the event a dog gets it most vets treat with the antibiotic Albon. Which also doesn’t kill but slows it down enough that the dog can clear the infection himself… eventually.

Nearly all dogs in the northeast USA will have contact with these protozoa. Most will have developed an immunity by adulthood. Which is good news, I guess.

I hate them. They’re so hard to prevent and treat. Really awful stuff.

Prevention

You know what they say, an ounce of prevention is worth a pound of cure?

I recommend you regularly deworm your dog. Late spring and late fall each year if you’re very active with your dog or live in a rural area.

Or late fall each year if you don’t go anywhere.

You may not see parasites in stool visually unless you just treated with medication. Just because you don’t see parasites in your dog’s poop does not mean your dog doesn’t have them.

The best broad spectrum dewormer is fenbendazole. A 3-5 day course does the trick. That’ll treat roundworms, whipworms, hookworms, one type of tapeworm and giardia.

You can easily do this at home with a dewormer purchase from any pet or farm supply store.

I do recommend having yearly tests run to check for parasites, but a negative exam does not necessarily mean your pooch is free from parasites. The safest approach is to run tests and then treat prophylactically with a safe, well tolerated broad spectrum anti parasitic medication once or twice a year.

And try to prevent your pup from drinking from puddles and waterways and from eating anything found outside.