It is common for pet owners to notice worms in their dog or cat’s feces and become concerned. Intestinal worms such as roundworms, hookworms, whipworms, and tapeworms are internal parasites that live in the digestive system and can cause a variety of health problems. The good news is that there are safe and effective dewormers available that can eliminate worms in pets. However, pet owners often wonder if worms will continue to be present after treatment.
How dewormers work
Deworming medications like fenbendazole, pyrantel pamoate, or praziquantel work by paralyzing and/or starving the worms. This causes them to detach from the intestinal lining and be passed out of the body through the feces. Some dewormers dissolve the worms, while others immobilize them so they are expelled while still alive. The medications are very effective when given at the proper dosage and interval. However, they kill the adult worms present at the time of dosing. They do not continue working to kill new worms that may hatch or be ingested afterwards.
Why worms may still be seen after deworming
There are a few reasons why pet owners may still see evidence of worms after treating their pet with a dewormer:
Immature forms not eliminated
Many intestinal worms have a life cycle that includes egg, larva, and adult stages. Deworming medications only kill the adults and sometimes larval forms. They do not act on the eggs. So if a pet has a heavy parasite burden, there may be many eggs still present in the intestinal tract that will continue to hatch and be passed in the feces after treatment. This is especially common with tapeworms and roundworms.
Reinfection
Dogs and cats sharing a household or environment can easily transmit worms back and forth. So even if all the worms in a pet’s body are eliminated with deworming treatment, they can easily pick up new ones through contact with an infected animal or contaminated soil or feces. Reinfection is common when proper environment hygiene is not maintained.
Medication was not 100% effective
While modern dewormers are very effective, they do not work 100% of the time. Factors like an incorrect dose or administration, high parasite burden, or resistance can sometimes lead to a portion of the worms surviving treatment. These worms may continue to be shed after dosing. Using repeated treatments can help fully eliminate any remaining worms.
A different worm species is present
There are four main types of intestinal worms in dogs and cats. If a pet is treated with a medication that targets one worm species (e.g. roundworms), other species (e.g. tapeworms) will not be affected. So tapeworm segments may still be visible after treating with fenbendazole, which only kills roundworms and hookworms. Using a broad-spectrum dewormer or rotating medications can help fully deworm pets.
How long after deworming are worms visible?
Adult worms that were weakened but not killed by a dewormer are typically passed in the first 1-3 days after treatment. Tapeworm segments may continue to break off and be passed for 1-2 weeks. Eggs and larvae already in the body will continue maturing and being passed for a few weeks after dosing. But over time, their numbers will diminish as the medication clears all the stages from the pet’s system. Multiple doses are often needed to fully remove a significant parasite burden.
Here is a table showing the lifespan and visibility after deworming for common intestinal worms in dogs and cats:
| Worm Type | Adult Lifespan | Visibility After Deworming |
|---|---|---|
| Roundworms | 5-10 months | Eggs visible for ~3 weeks |
| Hookworms | 2-3 months | Eggs visible for ~6 weeks |
| Whipworms | 3-6 months | Eggs visible for ~2 months |
| Tapeworms | 2-4 months | Segments visible for 1-2 weeks |
Tips to fully eliminate an intestinal worm burden
To ensure all stages of worms are cleared from a pet’s body after treatment, veterinarians recommend:
- Retreat in 2-4 weeks to kill newly hatched worms
- Use a broad spectrum dewormer to target all species
- Treat all pets in the household to prevent reinfection
- Practice environmental hygiene to remove eggs and larvae
- Conduct fecal testing to confirm worms are gone
- Use preventives like monthly heartworm medication
With diligent treatment and prevention, it is possible to fully eliminate an intestinal worm infestation in pets. But worms may still be visible for a period after an initial deworming treatment. Multiple doses are often needed to completely clear an infection. If worms continue to be observed after two or three rounds of deworming, veterinary advice should be sought to evaluate other options.
How to prevent reinfection after deworming
To prevent pets from getting reinfected with intestinal worms after treatment, it is important to:
- Clean up feces promptly in the yard to prevent environmental contamination
- Disinfect living areas with pet-safe products
- Bathe and groom pets regularly
- Prevent hunting and scavenging behaviors
- Treat boarding facilities and parks
- Administer preventives like heartworm medication
- Avoid contact with stray/feral animals
Controlling worms in the environment through proper feces disposal and cleaning is key. Worm eggs and larvae can survive for long periods in soil, grass, carpets, dirt, and sand. Keeping play areas and living spaces as sanitary as possible can help block transmission pathways. Monitoring pets for signs of reinfection and conducting periodic fecal tests is also recommended. With diligence, reinfection can be minimized after clearing an intestinal worm burden.
Conclusion
It is common to continue seeing worm eggs or segments in a pet’s feces after deworming treatment. This does not necessarily mean the medication wasn’t effective. Most dewormers work by killing the adult worms but do not destroy immature egg or larval stages. Inadequate environmental hygiene can also lead to reinfection after treatment. Using repeated, broad-spectrum dewormer doses, treating all in-contact animals, and thorough cleaning can help eliminate worms from a pet’s body and environment. While worms may still be visible immediately after treatment, following veterinarian recommendations can clear an infection and prevent recurrence. With vigilance, it is possible to fully rid a pet of their intestinal worm burden and return them to good health after a proper deworming protocol.