Worms in dogs – How to recognize and treat a worm infestation in time 🐶💩
- Beat Keller
- Jun 30, 2025
- 7 min read
Worms in dogs are among the most common parasites that can infect dogs. What's particularly insidious is that the infestation often goes undetected for a long time. In this blog post, you'll learn how to recognize the signs early, what types of worms there are, and how to effectively protect your dog.
What are worms anyway?
The so-called endoparasites are divided into two groups:
Threadworms such as roundworms, hookworms, whipworms, heartworms & lungworms
Tapeworms such as dog tapeworm, fox tapeworm or the cucumber seed-shaped tapeworm
They usually nest in the dog's small intestine and can cause considerable damage there.
How do dogs get infected with worms?
A worm infection usually occurs through the ingestion of:
✅ contaminated feces of other animals
✅ infested prey (e.g. mice)
✅ Worm eggs in soil, water or on grass
✅ infected fleas or raw meat
Puppies can also become infected through their mother’s milk – therefore early testing is particularly important.
Common symptoms of worm infestation
Some worms are visible to the naked eye in feces—like "living spaghetti." Others, however, remain invisible. Here are some signs to look out for:
Loss of appetite or cravings
Weight loss despite normal feeding
Bloated stomach (especially in puppies)
Vomiting or diarrhea (sometimes with blood)
Dull coat, itching around the anus
“Sledding”: The dog slides across the ground with its bottom
Noticeable “rice grains” in the feces or fur (tapeworm segments)
Worms in dogs – what types of worms are there?
🌀 Roundworms
Roundworms are among the most common worm species in dogs and cats. Infection usually occurs through the mouth—for example, through eating contaminated food, grass, soil, or contact with the feces of other animals. Particularly insidious: Roundworms can also be transmitted to humans , thus posing a risk to the entire family.
Puppies can become infected with roundworm larvae even in the womb. The larvae are passed through the placenta and thus enter the unborn dog's body before birth. Even after birth, the danger is not eliminated: Puppies can become infected with roundworms again through their mother's milk – and this can happen repeatedly.
Therefore, the first deworming of puppies begins as early as the second week of life. Deworming then takes place every two weeks and continues until approximately two weeks have passed since the last suckling by the mother dog. This is the only way to ensure continuous protection against the ever-present possibility of worm infestation.
🪝 Hookworms
As with roundworms, hookworms are usually transmitted through contact with infected feces. However, in this case, it may be enough for your dog to simply sniff it — making infection particularly easy . Hookworm larvae are also capable of penetrating the body through the skin and reaching the bloodstream. They also represent a potential source of infection for humans .
Hookworms are widespread throughout Europe, but are particularly common in regions with a tropical or subtropical climate.
Severe infestation can have serious health consequences, including:
bloody diarrhea
Weight loss
Growth delays in puppies
and in the worst case, anemia (anemia) due to blood loss in the intestine
📏 Tapeworms
Tapeworm infection occurs via an intermediate host, such as the consumption of mice or the ingestion of fleas. These intermediate hosts serve as carriers of the larvae, which, once ingested, can lead to an infestation in the dog's intestine.
Tapeworm infestation is detected macroscopically— that is, by visual examination of the dog's feces. In advanced infestations, tapeworm segments can often be seen directly at the anus or in the surrounding fur.
🫁 Lung & heartworms
Lungworms in dogs are also a growing threat in Switzerland. Originally, they were primarily found in southern countries, but are now also occurring in our latitudes – particularly in the Lake Constance area and in regions with mild climates. Lungworms are transmitted through intermediate hosts such as snails or frogs. Often, it is sufficient for the dog to lick grass contaminated with mucus – direct contact with snails is not necessary.
The symptoms of a lungworm infection are initially nonspecific and can easily be confused with other diseases. Typical signs include a chronic cough, shortness of breath, panting at rest, reduced energy, or general fatigue. In severe cases, blood in the stool or nosebleeds may also occur. If left untreated, a severe infestation can even lead to life-threatening complications such as clotting disorders or severe lung problems.
Heartworms (Dirofilaria immitis) pose a serious threat to dogs – even though they were originally prevalent primarily in Mediterranean countries such as Italy, Spain, Greece, and southern France. Due to climate change and increased pet travel, heartworms are now also occurring in Central Europe and increasingly in Switzerland. Transmission occurs exclusively through mosquitoes that have bitten animals infected with larvae. Direct transmission from dog to dog is not possible.
If a dog is infected with heartworms, the worms settle in the pulmonary artery and eventually in the heart. There, they can cause significant damage. Symptoms develop gradually, making early detection difficult. The first signs are often a chronic cough, rapid fatigue, shortness of breath, weight loss, or reduced performance. In advanced stages, cardiovascular problems and even life-threatening heart failure can occur.
The long incubation period is particularly insidious: It can take up to seven months after infection for the first symptoms to appear or for the parasites to be detectable in the blood. Reliable detection is usually only possible with a special blood test, which is only conclusive five to six months after infection at the earliest.
Prevention is especially crucial for dogs traveling to southern countries. After a stay in a high-risk area, the dog should be treated with a suitable dewormer 21 to 30 days after returning. In severely affected regions, regular preventative treatment may also be recommended—especially during mosquito season.
Conclusion : Heartworms aren't just a problem in southern countries – the risk is also increasing in Switzerland due to imported mosquito species and milder temperatures. Careful travel planning, targeted prophylaxis, and timely testing are crucial to protecting your dog from this dangerous parasite.
🦠 Excursion: Giardia in dogs – when diarrhea becomes chronic
Giardia are microscopic single-celled organisms that can infect your dog's small intestine and multiply rapidly there. Especially in puppies and young dogs, but also in immunocompromised animals, they often lead to persistent, mucous, or recurring diarrhea. However, even dogs with no symptoms can be infected with Giardia – and infect others.
Transmission usually occurs through contaminated water, feces, or contact with infected conspecifics. What's particularly insidious is that Giardia cysts are extremely resilient and can survive in the environment for up to several weeks – even under adverse conditions.
Reliable detection is only possible through a special stool test in the laboratory .
Treatment is usually carried out with special antiparasitic medications and a strict hygiene routine: food and water bowls must be cleaned daily with hot water, and sleeping areas and blankets must be washed and disinfected regularly. Regularly showering the bottom can also help prevent reinfection.
Conclusion: Giardia is persistent – but can be easily controlled with the right diagnosis, consistent hygiene and targeted treatment.
How is a worm infestation diagnosed?
💩 Fecal examination at the vet or home test: Collect small amounts of feces for at least three days and have them tested. This allows for reliable detection of worm eggs that are not constantly excreted.
This is how a dog stool examination works – an insight from practice
To give you an idea of how a dog stool test is carried out and what a test result might look like, I would like to show you a practical example here.
📦 In the following photo, you can see three stool samples collected on three consecutive days. This so-called collective sample is particularly important because parasites such as worms or Giardia do not shed their eggs or cysts every day. Collecting the samples over several days significantly increases the validity of the test. The samples should be refrigerated until sent to the laboratory to prevent the proliferation of germs.
🔬 The next two photos show the test results you receive after the analysis from the lab. In this case, in addition to worm infestation, they also tested for Giardia.
💡 Such a test not only provides clarity on whether acute deworming is necessary, but also helps avoid unnecessary medication. This is not only gentler on your dog but also a valuable contribution to combating resistance.
How often should a dog be dewormed? Individual risk assessment matters!
The rule of thumb used to be that every dog should be dewormed three to four times a year. However, this recommendation is now outdated. Today, instead, the focus is on an individual risk assessment tailored to each individual animal—and that's a good thing!
Whether and how often a dog should be dewormed depends on several factors:
Age of the dog
Type of housing (e.g. apartment or outdoor access)
Nutrition (e.g. raw feeding or BARF)
Contact with other animals
Stays in parasite risk areas (e.g. abroad, south)
Particularly at risk are:
Puppies , as their immune systems are not yet fully developed
Dogs living in larger groups or shelters
Dogs with free running , e.g. mouse hunters or farm dogs
Animals that regularly receive raw meat or offal
If you're unsure how high your dog's actual risk is, we recommend quarterly deworming ( four times a year) to be on the safe side. Alternatively, regular stool examinations can help you deworm specifically and only when needed.
💡 Tip: A well-thought-out parasite prophylaxis not only protects your dog – but also you and your family from zoonoses such as the fox tapeworm.
There is no general answer – the appropriate deworming depends on living conditions and risk of infection.
💡 Important: Dewormers are not preventative—they only eliminate existing worms. Regular monitoring is therefore crucial!
How to protect your dog (and yourself!)
✅ Hygiene : Always remove dog excrement immediately and dispose of it in the household waste
✅ Flea protection : Fleas transmit tapeworm eggs!
✅ Wash your hands after contact with feces, soil or the dog
✅ Do not let mice hunt – especially in fox tapeworm areas
✅ Conduct stool tests at the vet or using a home test kit
Conclusion: Worm infestation in dogs is treatable – if you detect it early
Worms are unpleasant, but there's no reason to panic. With a watchful eye, regular checkups, and the right preventative measures, you can reliably protect your four-legged friend. 🐶❤️
