Internal (gut or heart) parasites are common in puppies and adult dogs. Some puppies may even be born with worms that they contracted during gestation. Dogs can also get parasites from infected environments or from ‘intermediate host’ insects.
Oftentimes, worms in dogs hide in plain sight — with pet parents only becoming truly sure of the worms’ presence when they show up in vomit or poop. When this happens, it usually means that the parasitic infestation is already moderate or advanced.
Would you like to take the guesswork out of detecting worms in dogs? If so, this complete guide covers everything you need to know. Read on to learn more about the most common types of internal parasites in dogs and what red flags to watch out for.
What are Worms in Dogs?
Worms in dogs are internal parasites that, in one way or another, feed off the dog’s nutrients. These worms also have different life cycles which influence:
- where they live in the dog’s system;
- how they are transmitted; and
- what symptoms they manifest.
An entire branch of veterinary science (veterinary parasitology) is dedicated to studying worms in dogs and their pathogenesis. In the following sections, we distill key parasitology information that every dog parent needs to know.
Most Common Types of Worms in Dogs
1. Hookworms in Dogs
Intestinal | Zoonotic | Pathogenic
Where Hookworms in Dogs Reside
Hookworms in dogs are intestinal parasites that latch onto the intestinal wall where they feed on blood. Hookworms get their name from the ‘hook’ they have on their mouths to securely latch onto intestinal walls. Hookworms in dogs are also capable of migrating to the lungs via the bloodstream; then, they are coughed up and swallowed, thereby going back to the intestines.
Hookworm Species That Infect Dogs (+ Risk Level for Humans)
There are three main hookworm species that infect dogs and puppies: Ancylostoma caninum, Ancylostoma braziliense, Uncinaria stenocephala. These species can also infect humans, meaning that hookworms in dogs are considered ‘zoonotic’.
How Hookworms in Dogs are Transmitted:
Hookworms in dogs can be transmitted in the following ways:
- To unborn pups: from the mother’s placenta
- To newborn pups: from infected breast milk
- To newborn pups: from the stool of other infected puppies in the litter
- To puppies and dogs: from the stool of infected dogs or cats
- To puppies, dogs, and humans: from contaminated soil
Note: Both humans and pets can contract hookworms from contaminated soil in two ways: ingestion and direct skin contact. This is why eating unwashed vegetables is a common risk factor for contracting hookworms. Walking barefoot (or ‘bare paw’) on contaminated soil is also a risk factor because small hookworm larvae can burrow into the skin.
Symptoms of Hookworms in Dogs
So what are the clues that a dog is possibly suffering from hookworms? Watch out for these symptoms:
- Weight loss
- Lethargy (lack of energy)
- Anemia
- Dark or bloody stool
- Worms in dog vomit
- NO worms in dog poop (unlike some other worms, the life cycle of hookworms does not involve the worms being passed into the dog’s stool. Only eggs are passed into the stool AND these eggs are microscopic.)
2. Tapeworms in Dogs:
- Intestinal | Zoonotic (low risk for humans) | Rarely causes serious disease in dogs
Where Tapeworms in Dogs Reside
Tapeworms in dogs are intestinal parasites that cling to the dog’s intestinal walls. Tapeworms get their names from their flat body, which resembles a thin piece of tape. Unlike some other worms in dogs, tapeworms are not known for migrating to other systems apart from the intestines.
Tapeworm Species That Infect Dogs (+ Risk Level for Humans)
The main species of tapeworm that infects dog are called ‘Dipylidium caninum’. Although they are considered ‘zoonotic’ (or can be transmitted to humans), the chance of humans getting tapeworms from dogs is relatively low. This is because of how tapeworms are transmitted.
How Tapeworms in Dogs are Transmitted:
The most common tapeworm found in dogs (D. caninum) needs an 'intermediate host’ to infest and spread: the flea. The tapeworm egg is first ingested by a flea larva. Once the infected flea larva matures, it is capable of transmitting tapeworm.
The infected adult flea needs to be ingested for the parasite to be transmitted. Dogs might ingest infected fleas while chewing on irritated skin because of flea bites. Humans can get this type of tapeworm too — but only after accidental ingestion of an infected flea, which is rare.
Symptoms of Tapeworms in Dogs
As mentioned earlier, tapeworms in dogs rarely produce serious illness. However, there are still clues that pet parents can look for, such as:
- NO worms in dog poop - instead, infected dogs pass ‘proglottids’ (a segment of the tapeworm which contains eggs and is about 0.5–1.5 cm in length)
- Anal scooting (i.e. the scraping of the dog’s anal region against the floor, grass, etc. which helps to relieve itching in the region)
- Weight loss & worms in dog vomit - rare, in cases of heavy tapeworm infestation
3. Intestinal Roundworms in Dogs
Intestinal | Can be zoonotic | Pathogenic
Where Roundworms in Dogs Reside
Intestinal roundworms in dogs live freely (unattached) in the intestinal walls. There, roundworms feed off partially digested food. Roundworms get their name from the round or tube-like shape of their body. Before residing in the intestines, the life cycle of roundworms requires them to migrate to other tissues such as the lungs and liver.
Roundworm Species That Infect Dogs (+ Risk Level for Humans)
The main species of intestinal roundworms in dogs include Toxocara canis and Toxascaris leonina. Both can be treated the same way. The only significance of determining the roundworm species a dog has is to find out who else could be at risk. Toxocara canis is zoonotic, meaning it can infect humans. Meanwhile, Toxascaris leonina is NOT zoonotic — but it can also infect cats.
How Roundworms in Dogs are Transmitted:
Roundworms in dogs can be transmitted in the following ways:
- To unborn pups: from the mother’s placenta
- To newborn pups: from infected breast milk
- To puppies and dogs: from infected stool
- To puppies, dogs, and humans: from contaminated soil
Symptoms of Roundworms in Dogs
So how does a pet parent know if their dog might be infected with roundworms? Here are some telltale symptoms:
- Dull hair
- Weight loss (but with a potbellied appearance)
- Diarrhea
- Worms in dog vomit
- Worms in dog poop (they’re more likely to show in poop because they are not attached to the intestinal wall)
4. Whipworms in Dogs
Intestinal | Not Zoonotic | Pathogenic
Where Whipworms in Dogs Reside
Whipworms in dogs reside in the large intestines, attached to the intestinal wall. They get their name from the whip-like shape of their body which is blunt on one end and tapers toward the other end. Unlike some other worms in dogs, whipworms do not migrate outside of the digestive system.
Whipworm Species That Infect Dogs (+ Risk Level for Humans)
The main species of whipworm that infects dogs is called Trichuris vulpis. This species is NOT zoonotic, meaning these whipworms cannot infect humans.
How Whipworms in Dogs Are Transmitted:
Whipworms in dogs can be transmitted among puppies and dogs: from infected stool or contaminated soil.
Symptoms of Whipworms in Dogs
So how can one tell if a dog is infected with whipworm? Look for the following symptoms:
- Weight loss
- Lethargy (lack of energy)
- Diarrhea (which may contain blood and mucus)
- Vomiting
- Worms in dog poop (more common with heavier infestations)
5. Heartworm in Dogs
Lungs & heart | Zoonotic (low risk for humans) | Can be fatal for dogs
Where Heartworms in Dogs Reside
Heartworms are one of the most dangerous worms in dogs on this list because of where they reside in a dog’s system. Heartworms inhabit the lungs, heart, and associated blood vessels where they feed off the host’s blood. Because heartworms are large and inhabit delicate vital organs, they can cause serious health damage involving internal inflammation, blood vessel blockage, heart failure, and pulmonary insufficiency. All cases of heartworm in dogs are potentially fatal.
More About Heartworm (+ Risk Level for Humans)
Heartworm is actually a species of roundworm. However, due to the prevalence of this specific parasite, the subtlety of its transmission, and its potentially fatal effects on dogs, heartworm deserves an entire section of its own in this guide.
The species of heartworm in dogs is known as Dirofilaria immitis, a type of roundworm that can also infect cats and ferrets. Humans can also get heartworm, although not directly from dogs. In addition, humans are 'suboptimal hosts' for heartworm, meaning the worms can, in rare cases, infest the human body (and may cause health problems along the way), but they typically die if they try to get to the heart, thereby dying out before they can reach maturity.
How Heartworm in Dogs is Transmitted:
The only way heartworm is transmitted to dogs, cats, or ferrets is through the bite of an infected mosquito that’s carrying the heartworm larva. Similarly, humans cannot get heartworm unless they are bitten by an infected mosquito. However, having a pet that is infected with heartworm also increases the chances of humans (and other pets in the household) being bitten by an infected mosquito.
Symptoms of Heartworm in Dogs
So what are the signs that a dog is suffering from a heartworm infection? Look out for the following symptoms:
- Persistent coughing
- Shortness of breath
- Reduced appetite
- Weight loss
- Lethargy (lack of energy)
- Aversion or reluctance to exercise
- Nose bleeds
- High blood pressure
- A swollen abdomen (more common in heavy infestations)
Diagnosing Worms in Dogs - Can It Be Done at Home?
Although this guide is helpful in letting pet parents know what red flags to watch out for when it comes to detecting intestinal parasites in dogs, only a licensed veterinarian can conclusively diagnose worms in dogs.
To accurately diagnose a parasitic infection in a dog, veterinarians use tests like fecal flotation (which involves microscopic examination of a fecal sample to look for worm eggs) and/or fecal antigen testing (which detects parasite proteins). Of the two, the latter is considered to be more accurate.
Note: Fecal flotation and fecal antigen testing can also be used to detect giardia, a unicellular parasite that causes giardiasis, a diarrheal disease.
It is highly recommended for pet parents to consult a veterinarian after seeing symptoms of a possible worm infestation in a dog.
Are Worms in Dogs Life Threatening?
All internal parasites mentioned in this article can cause serious symptoms and, in some cases, death. Some internal parasites may also leave behind long-term health complications, even after the dog is treated — these complications can include stunted growth due to an intestinal worm infestation or damaged blood vessels due to a heartworm infestation.
As further explained by Sploot’s Medical Director, Dr. William Bryer: “The severity of the disease [caused by worms in dogs] varies based on a lot of factors, including worm burden, the length of infection, the health and age of the pet, and the type of worm [...] Some worms, such as heartworm, can be lethal.”
Are There Seasons When Parasites Are More Common in Dogs?
Although dogs can get internal parasites during any season, intestinal worms and heartworms show seasonal prevalence — as detailed below:
- Hookworms, roundworms, and whipworms - are seen to be prevalent from December to February — and from July to August
- Tapeworms - are seen to be prevalent when fleas (the intermediate host) are most active, which is typically from summer to late fall.
- Heartworm - is seen to be prevalent when mosquitos (the intermediate host) are most active, which is typically from early spring to early fall, peaking in the summer season.
How to Prevent Worms in Dogs & Puppies
When it comes to internal parasites in dogs, prevention is always better than cure. Here are ways to prevent worms in dogs and puppies.
1. Deworm Puppies
Deworming is essential for puppies because they can contract parasites before they are born or while nursing. Symptoms of internal parasites also tend to be more serious in puppies.
Deworming medication for puppies is typically administered orally and follows a recommended schedule. Get in touch with your veterinarian to get started on puppy deworming.
2. Give Heartworm Preventives to Adult Dogs
As for adult dogs, administering heartworm preventives is a must. This is because heartworm causes severe symptoms and can lead to death, even in adult dogs. In addition, most heartworm preventives are also effective against certain species of intestinal worms.
Note: Heartworm preventives for adult dogs can be administered orally or via injection. Consult your veterinarian to get the best heartworm preventives for your adult dog.
3. Check & Treat External Parasites Promptly
Tapeworms are transmitted through fleas. Therefore, checking for fleas and promptly taking measures against this external parasite will help dogs avoid tapeworm infection.
While on the subject of flea prevention, we’d also like to remind pet parents to be equally wary of ticks. Ticks can carry disease-causing bacteria, viruses, and unicellular parasites. A few examples of diseases that ticks can carry include Lyme disease, Rocky Mountain Spotted Fever, and tickborne relapsing fever.
4. Regular Wellness Exams
Another important component of preventive care for adult dogs is scheduling regular pet wellness exams. These help prevent a wide range of illnesses, including parasites.
At Sploot, we encourage clients to get yearly heartworm testing along with regular wellness exams. Our veterinarians may also recommend yearly fecal antigen testing, especially for dogs that have a high risk of getting infected with internal parasites — this includes dogs that hike regularly, visit dog parks, stay in dog boarding facilities, etc.
When parasites are detected early (with the help of the above tests), treatment is more straightforward (i.e. deworming medication). Advanced parasitic infestations may require surgery.
Final Thoughts About Worms in Dogs
We hope you found this guide about worms in dogs helpful. We covered everything from worm symptoms to strategies for parasite prevention! If you have any specific questions about worms in dogs, consult your veterinarian.
Sploot Veterinary Care is always here to help! We are a primary & urgent care veterinary clinic with multiple vet clinic locations, operating for extended hours. If you’d like to get started on parasite prevention or treatment, book an appointment today. Our experienced veterinary professionals will instruct you on the next steps.
Till next time, we’re with you every pounce of the way!
