Taenia pisiformis infections are common in dogs in North America.
It is a flatworm that lodges in their small intestine and is formed of segments containing the parasite's eggs.
Each egg contains an embryo with two rows of hooks allowing them to cling to the intestinal cells of the animal.
The infection is very often unseen.
However, the dog can occasionally suffer from itching caused by the passage of segments of the parasite through the anus. It is also common to see these segments, which resemble grains of rice, mobile or immobile, in the hairs of the perianal region.
The dog is the definitive host of the parasite, that is, the host in which the parasite matures.
It is infected by biting a rabbit, the intermediate host of the parasite (host in which one of its development phases occurs), while hunting.
Digestion of the prey by the dog frees the parasite present in its viscera. It clings to the intestinal cells of its host and continues its development.
Once the worm has reached maturity, segments, called proglottides, which are filled with eggs, separate from the adult worm and are expelled with the dog's stool.
When a rabbit ingests the eggs in the environment, larval cysts develop there and remain hidden in its viscera until it is eaten by a dog.
Adult worms in their intestines begin to excrete proglottides in their stools a month and a half to two months after infection.
The eggs remain alive in the environment for up to one year under ideal climatic conditions, ie low temperature and high humidity. However, they are sensitive to drought and can only survive for one week.
As mentioned earlier, dogs become infected by eating rabbits.
Although isolated cases of contamination in humans from infected dogs have been reported, the overall risk of such transmission appears to be extremely low in North America.
The presence of the flat worm segments in the perineal hair of a hunting dog confirms the infection.
You can also crush one of these segments between a slide and a coverlsip and check the sample under a microscope to visualize the eggs. These are spherical and have a thick double striated wall: the outer wall is dark while the inner wall is lighter.
Attempting to confirm the infection by examining a stool sample through fecal flotation with a microscope is often disappointing because proglottids are not evenly distributed in the stool and eggs do not always float.
Although the infection is rarely associated with symptoms, it is recommended to treat it for aesthetic and hygienic reasons.
There are various medications, sold under prescription, that are effective and safe to kill the parasite.
Preventing dogs from hunting by keeping them on a leash or in a fenced yard is a good way to limit the risk of infection with the parasite.
Otherwise, it is recommended that they be administered medication preventively every month during the hunting season.