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The microscopic world of intestinal parasites (IP) may seem unnoticeable, but this world really exists. It should be known that pets’ IPs have the potential to be transmitted to humans (zoonosis1). Some individuals are more vulnerable to zoonoses: the elderly and immunocompromised, young children, as well as pregnant women.

Here are the most common modes of propagation:

In our animals

  • Ingestion of eggs, cysts2 or larvae in excreta, wild animals or contaminated water;
  • By the placental barrier;
  • By breast milk;
  • By penetrating larvae into the skin.

In humans

  • Ingestion of eggs found on soiled food, animal hair or on hands soiled with contaminated soil;
  • By penetrating larvae into their skin.

In North America, the IPs encountered are well adapted to our climate. They belong to the kingdom of the protozoa, or to that of the helminths (worms). In the reign of protozoa we find giardia and coccidia. In the helminths worms; rounds (roundworms), with hooks (hookworms), whip (whipworms) and flat (tapeworms).

Some texts speak of whipworm as hookworm, but in most cases it is a hook worm. The whipworms are definitely worms.


The giardia

Giardia affects different mammals, including humans, and is the most common protozoan. It causes fever, diarrhea with sometimes blood. It produces a zoonosis.

 Cycle of giardia3



This protozoan destroys the intestinal cells and hinders the absorption of food. Very common in young animals, the symptoms are chronic diarrhea sometimes bloody and stunted. Many animal species can be affected, and this infection can be transmitted to humans.




Eggs of roundworm in the dog observed under a microscope.
© Flukeman, Creative Commons

The roundworm larvae develop into adults in the intestines of animals. These worms lay microscopic and extremely hardy eggs that survive for several years in the environment once defecated by the host. 

They are especially worrying for puppies and kittens because they cause a decrease of the immune system, a slowing of growth, digestive, respiratory and skin disorders. Too many in the digestive tract of a young animal, roundworms can obstruct the intestine.

In humans, ingested larvae can migrate to organs such as the eye or the brain.



As its name suggests, this worm clings to the intestinal wall and feeds on the blood of its host. This loss of blood causes a decrease in vitality in the young animal. Adults will have symptoms of diarrhea and weight loss.

In humans, larvae, housed under the skin, cause skin irritation in the form of a serpiginous groove. These lesions cause reddish itching, but they are easily treated once diagnosed.

Whipping Worms

Whipworms also feed on blood in the digestive tract of dogs and cats. They cause bloody diarrhea that can be fatal. Repeated treatments are necessary to eliminate this parasite.

It is also a zoonosis for humans where it causes a skin infection with serpiginous eruptions as for hookworm. If the infestation is severe, they can cause anemia.


Tapeworm cycle in cats

Common tapeworms are not considered zoonoses for humans. Cats are more likely than dogs to have a tapeworm. They catch it by ingestion of fleas and rodents who are the intermediate hosts. Flea elimination is without a doubt the first step in protecting your cat against tapeworm. It is the segments of the worm (rice grains) that are released into the environment.



Here are some preventative ways to eliminate and prevent IP infection: :

  • Control fleas on your animals;
  • cover children’s sand squares;
  • wash your hands, bedding and children’s toys regularly;
  • never drink water from a watercourse or lake;
  • wear gloves when working in the ground outdoors;
  • prevent the hunting behaviour of cats;
  • collect and discard excrement;
  • deworm adults two or three times a year;
  • deworming puppies and kittens at regular intervals several times in the first year of life.

In conclusion, regular deworming of your pets is important and remains the best way to protect your family from intestinal parasites that can cause zoonosis!


@ Martine Lavallée, B.A.A. and animal health technician


1A zoonosis is a disease that can be transmitted from animals to humans and vice versa.

2 A cyst has a strong outer layer and is able to survive in extreme environmental conditions for years.

3 Image collected on

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