Taenia pisiformis infections are common in cats 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.
Occasionally, a large amount of worms can cause intestinal obstruction requiring surgery.
The cat is the definitive host of the parasite, that is, the host in which the parasite matures.
It is infected while hunting by ingesting a rodent, the intermediate host of the parasite (host in which occurs one of its development phases).
Digestion of the prey by the cat releases the parasite present in its liver. It clings to the intestinal cells of its host and continues its development.
Once the worm reaches maturity, segments, called proglottides, which are filled with eggs, separate from the adult worm and are expelled with the cat's stool.
When a rodent ingests the eggs in the environment, larval cysts grow there and remain hidden in the liver until it is eaten by a cat.
The parasite's life cycle can last up to three months. It begins when the cat becomes infected with eggs in the intermediate host and ends when adult worms in its gut excrete proglottides in its stool one month 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.
Adult worms can live in cats for as long as thirty-four months.
As mentioned earlier, dogs become infected by eating rodents.
Although isolated cases of contamination in humans from infected cats 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 cat that hunts 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.
Keeping cats indoors to prevent them from hunting is the best way to prevent infection.
Otherwise, it is recommended that they be administered medication preventively every month during the hunting season.