Heartworms, ticks, fleas and intestinal worms—how much do you know about these critters? As pet owners we should all be aware of the parasites that can wreak havoc on your pet’s health and happiness, and good practices to prevent infection.

The most important reason for prevention, of course, is to spare your pets from the discomfort of some potentially fatal diseases spread by parasites. Heartworm disease, for example, is severe and treatment is expensive, stressful and in many cases unsuccessful. The number of heartworm and tick-borne disease cases have been on the rise in southern Ontario (especially Toronto) over the past few years. In 2015 in RVVH, 6% of dogs that were screened for Lyme disease tested positive. For that reason, testing and prevention are more important than ever.

Scroll down to learn more about the most common parasites and prevention.


What is heartworm disease, anyway?

In a nutshell, heartworm is a dangerous blood-borne parasitic worm that is spread by mosquitoes.

When the infective heartworm larvae are deposited in a dog or cat through a mosquito bite, they move through the blood stream and set up camp in the pulmonary arteries and heart, where they mature into adults that can grow to over a foot in length![1] For the duration of their lives (2–3 years in cats and 5–7 years in dogs), they wreck havoc on the animal’s heart and lungs, causing serious damage that can have fatal consequences if left untreated.[7,8]

In 2010, the Ontario Veterinary College at the University of Guelph did a survey on heartworm in Canada. 564 dogs were diagnosed with the disease in Canada—a 63% increase since 2002. The focus of infection continues to be in South-Western Ontario, where the prevalence of infection is much higher than the average for the province. Out of the 564 dogs nationwide that tested positive for heartworm disease in 2010, 76% were in Southern Ontario (figure 1).[1]

Why is prevention so important?

The most important reason for prevention, of course, is the severity of the disease once acquired. Treatment is expensive, hard to come by in Canada and is not always 100% effective. It is also risky—when the medication begins to kill the heartworms they are carried to the lungs and other parts of the body in the animal’s blood, potentially blocking blood vessels and causing allergic reactions. The number of heartworm and tick-borne disease cases have been on the rise in southern Ontario (especially Toronto) over the past few years. For that reason, testing and prevention are more important than ever.

Here is some links about the heartworm life cycle and heartworm disease in Ontario...

Heartworm Disease in Cats – Ontario Veterinary Medical Association
When should my puppy go on heartworm prevention? – PetPlace
10 Things You Need To Know About Heartworm Before It’s Too Late – BarkPost
Heartworm Life Cycle – American Heartworm Society
Heartworm Life Cycle (video) – Bayer, Youtube 

Heartworm Disease - Plain and Simple. Video by Else-Vet. [11]

Out of the 564 Canadian dogs that tested positive for heartworm in 2010,

figure 1. 76% of positive cases were in Southern Ontario.

Sure, ticks are gross, but are they dangerous?

Ticks are typically very small when unfed, only about 1–5 mm in length. They do not fly, they are sluggish, and their bites are not painful. So why do we worry?  

In the spring when the snow is melted and the earth thawed they position themselves on tall grass and bushes waiting for a host to latch onto. They may take several hours to find a suitable place on the host to attach to feed. All active stages feed on blood. Ontario ticks can potentially carry a number of diseases, the most prevalent being Lyme disease. In Ontario, Lyme disease is spread by the bite of blacklegged ticks (formerly called deer ticks), Ixodes scapularis (figure 1).[5] While both humans and animals can be infected with Lyme disease via tick bite, cases in people are much rarer. People usually find and remove ticks before they can transmit the disease, but it is often much harder to find ticks on our dogs and cats, especially on those with long or thick hair or fur. Quick removal is the best way to prevent infection after a tick bite—disease is more likely to be transmitted after the tick has been attached for 24 hours (figure 2).[5]

While the chances of your pet's catching Lyme or another tick-borne disease in Ontario are relatively low, the risk is greatly increased in certain pockets of the province that have a known infected tick population. The blacklegged tick can be found in rural parts along the shores of Lakes Erie and Ontario and the St. Lawrence River.[5] Locations with established blacklegged tick populations infected with Lyme disease include many popular national and provincial parks, one of which is our own Rouge Valley.[5] Where exactly these tick-rich areas begin and end is hard to say and populations continue to grow and expand. In 2015 at RVVH, 6% of dogs that were screened for Lyme disease tested positive.

Some common symptoms of Lyme disease include stiffness in legs and back while walking, sensitivity to touch, difficulty breathing, fever, lack of appetite, depression and swollen lymph nodes. Rarer symptoms can include heart and nervous system complications. 

Here are some links to more information about ticks and Lyme disease in Ontario:

Ticks in Rouge Park – Rouge Park
Early diagnosis crucial for pets with Lyme disease – Toronto Star
Tick Mythbusters – BarkPost
The Dangers of Ticks in Cats – PetPlace
Dogs and Ticks – IDEXX

figure 2. Probability of Transmission Over 96 Hours


Established tick populations carrying Lyme disease include many popular national and provincial parks, one of which is our own Rouge Valley.

figure 1. Blacklegged tick (formerly deer tick), Ixodes scapularis

Attack of the Fleas

Cat and dog fleas are tiny brown insects that live on your pets and feed on their blood. To make matters worse, they may even choose to snack on you—disgusting, we know.

Once fleas have landed on your pet they are one of the most complicated parasites to get rid of. They are very prolific—one flea can lay over 2000 eggs that fall off onto your pet’s bedding, near and under chairs, or even on your bed where your pet rests or sleeps.[3] It shouldn’t come as a surprise that eliminating a flea infestation in your home is very frustrating and can take many months.

Not only are fleas an obvious nuisance, they can also pose serious threats to your pet’s health. Some animals may develop flea allergy dermatitis (FAD), a highly allergic reaction to the flea’s saliva characterized by intense itching and scratching that can lead to hair loss, scabs, and other self-inflicted damage. Furthermore, fleas can transmit other parasites, such as tapeworm, if accidentally ingested.[6]

Here are some links to more information about fleas:

Fleas – Government of Canada
Essentials of Flea and Tick Control (video) – AnimalCareTV
The Amazing World of Fleas Part 1, Part 2 (video) – Else-Vet

The Flea Tapeworm in dogs and cats - Dipylidium caninum. Video by Bayer Jungle. [12]

For every flea you find, there are 100 still hiding.

Cat flea (ctenocephalides felis) under scanning electron microscope. Video by Jasenko Zivanov. [13]


What is it with worms and my pets?

What you need to know about intestinal parasites (worms) and your pet! Video from the Pet Health Network. [14]

While all dogs are susceptible to infections with intestinal worms, some are more vulnerable—namely puppies. This is why frequent visits for fecal examinations and deworming are fundamental to maintaining your puppy’s health as well as the health of other animals (including humans!) that may come into contact with infective eggs in soil and/or poop.

The most common intestinal parasites in dogs and cats are roundworms, tapeworms, whipworms, and hookworms.


Roundworms are one of the most common intestinal parasites in dogs and cats. In an adult dog, the story begins with the ingestion of an egg that hatches in the intestine during digestion. Newly hatched microscopic larvae move into the muscles where they lay dormant and are unlikely to cause problems…until pregnancy that is. When a dog becomes pregnant, dormant larvae are reawakened. They move through the placenta and into the puppies. Following birth, the tiny larvae move through the puppy’s bloodstream and up to the lungs, where they are coughed up and swallowed, ultimately reaching the intestine. Here they mature to adults and mate, laying eggs by the thousands, and the cycle repeats.[10] Puppies can also become infected through drinking their mother’s milk, which may also contain previously dormant roundworm larvae.

Heavy parasitic loads in your puppy’s intestines can cause a lot of abdominal discomfort and a potbelly, diarrhea, weakness and/or vomiting. They may even cause intestinal obstructions, which can be fatal if left untreated.[10]

Roundworm eggs are very hardy, and can survive in the environment for long periods of time. If a human accidentally ingests an egg, larvae hatch and migrate through the body, potentially causing serious problems. Children, who use their mouth as a third hand, are at a higher risk of accidental ingestion. Good hygiene, in combination with deworming and prevention can significantly reduce these risks. 

Roundworms of Dogs (and Cats) - Plain and Simple is a very funny an informative Youtube video by Else-Vet about roundworms.


Tapeworms can be transmitted to dogs (and cats) that ingest infected fleas or rodents. They attach to the intestinal wall and grow in length as segments which develop from the neck. They often reach lengths of over 2 feet![4] Eggs are found in many segments of the tapeworm, and are deposited within these segments into the poop of the host animal, where they can be seen with the naked eye. You may also find them on your pet’s rear end—they look like small, white pieces of rice that may even be moving (yuck). If your pet has been diagnosed with a flea infestation, a fecal test may also be necessary to check for tapeworms.

The Flea Tapeworm (Dipylidium caninum) - Plain and Simple is a very funny an informative Youtube video by Else-Vet about the flea tapeworm.


Whipworms are small whip-shaped worms (duh). Infection begins with the ingestion of infective eggs, which are found in the environment after being pooped out by other infected animals. Eggs hatch in the small intestine and mature to adults in the large intestine and colon, where they deeply embed themselves in the intestinal wall and cause inflammation and discomfort. Although most infections are asymptomatic, infected dogs may have diarrhea that is mucous-y or watery, foul smelling, and/or streaked with blood. Other signs include dehydration and weight loss.


Hookworms, more common in dogs than cats, are small, thin worms that attach to the wall of the small intestine with their sharp teeth and suck blood. They change their attachment site several times per day. Hookworm eggs are deposited in poop, and hatch in the environment. In adult dogs, infection usually begins with hookworm larvae penetrating the skin and migrating to the muscles, where they lay dormant.[10] Larvae may also be ingested from the environment. Dormant larvae can re-awaken from the muscles throughout the dog’s life and move to the intestine, where they lay eggs and feed on blood. Puppies, however, become infected with hookworms in their intestines after ingesting larvae in their mother’s milk.

Intestinal infections can cause blood loss and anemia, which can be significant enough to cause death in puppies that have ingested large amounts of larvae. Other signs of infections are weakness, weight loss, lameness and diarrhea.[10]

Hookworms also pose a threat to humans. Larvae from the environment may penetrate skin and begin to migrate underneath. That’s right… worms. crawling under your skin. This is another reason why pooping-and-scooping, combined with regular screening, treatment or prevention are so very important.

What are my prevention options?

The preventative medications we carry at RVVH work against all of the most common parasites—heartworm, ticks, fleas, and intestinal worms.

Most of the medications come in the form of a liquid that is simply dropped onto the skin between the shoulder blades once a month during parasite season (April–November). The medication enters your pet’s bloodstream and eliminates any parasitic larvae that may be present. The medication also kills ticks and fleas directly when they feed.

Heartworm Prevention

If your pet already has heartworm disease, introducing a preventative medication could kill existing heartworms too quickly, which would be dangerous. For this reason, we recommend a blood test be done before using preventative medications. If your pet has not visited us for a physical examination within the last year, an examination will be necessary before we can dispense any preventative medication.

Tick Prevention

It is imperative that you check your dogs (and outdoor cats) for ticks on a daily basis during parasite season, particularly during the spring and fall. This is especially true for pets that enjoy hikes and walks in rural or forested areas. Ticks should be removed (properly) as soon as possible. We can remove ticks for you at the hospital, or give you a special tool for removing them yourself. Tick prevention in areas known for ticks (including our own Rouge Park) should start as soon as temperatures rise to +4–5°C in the spring.

Flea Prevention

If you find a flea on your pet, it is very likely there are thousands more still hiding away, both on your pet and in your house. Contact us if you think your pet has fleas or if you would like to know more about treatment.

Intestinal Worm Prevention

Puppies and kittens should go through a number of deworming treatments (fecal test and medication) before reaching adulthood. Intestinal worms are very common in baby animals. A negative fecal test does not necessarily mean there are no parasites, it just means there are no eggs in the poop sample provided. For these reasons we recommend multiple deworming treatments for puppies and kittens. 

For adult animals we recommend fecal testing be done at least once a year to screen for possible infections. If a fecal test comes back positive, our treatment approach would depend on the type of parasite that was detected. Contact us if you think your pet has worms or if you would like to know more.

Remember, good hygiene should always accompany regular screening, treatment, and prevention of worms. PLEASE pick up your dog’s poop!

Call us if you would like to schedule an examination for your pet(s) or if you have any questions about prevention.


Parasite Season Information REFERENCES

1. J. Owen D. Slocombe. Rep. Heartworm in Canada in 2010. Ontario Veterinary College at the University of Guelph, 31 Mar. 2011. Web. 3 Apr. 2016.
2. Elsheikha, Hany, and Naveed Ahmed. Khan. Essentials of Veterinary Parasitology. Norfolk, UK: Caister Academic, 2011. Print.
3. "Fleas." Health Canada and the Public Health Agency of Canada. Government of Canada. Web. 01 Apr. 2016.
4. Mansourian, Erika. "Tapeworms in Dogs: Symptoms, Treatment, & Prevention."American Kennel Club. American Kennel Club, 15 Dec. 2015. Web. 04 Apr. 2016.
5. "Lyme Disease." Ontario Ministry of Health and Long-Term Care. Government of Ontario. Web. 01 Apr. 2016.
6. "PET HEALTH CORNER: Fleas and How to Beat Them." Ontario SPCA Blog. Ontario Society for the Prevention of Cruelty to Animals. Web. 01 Apr. 2016.
7. "Heartworm Disease In Cats." Ontario Veterinary Medical Association. Ontario Veterinary Medical Association. Web. 03 Apr. 2016.
8. "Heartworm Disease In Cats." Ontario Veterinary Medical Association. Ontario Veterinary Medical Association. Web. 03 Apr. 2016.
9. "Ticks in Rouge Park." Rouge Park. Rouge Park. Web. 01 Apr. 2016.
10. Traversa, Donato. "Pet Roundworms and Hookworms: A Continuing Need for Global Worming." Parasites & Vectors Parasit Vectors 5.91 (2012): 91. Web. 4 Apr. 2016.
11. Else-Vet. “Heartworm Disease - Plain and Simple.” Youtube. Youtube, 2 Jul. 2014. Web. 02 Apr. 2016.
12. Bayer Jungle. “The Flea Tapeworm in dogs and cats - Dipylidium caninum.” Youtube. Youtube, 19 Jun. 2012. Web. 02 Apr. 2016.
13. Jasenko Zivanov. “Cat flea (ctenocephalides felis) under scanning electron microscope.” Youtube. Youtube, 17 Dec. 2014. Web. 02 Apr. 2016.
14. Pet Health Network. “What you need to know about intestinal parasites (worms) and your pet!” Youtube. Youtube, 21 Mar. 2012. Web. 02 Apr. 2016.