Intestinal parasites in dogs: symptoms, tests and treatment

Overview

Canine intestinal worms include roundworms, hookworms, whipworms and tapeworms. Intestinal protozoa include Giardia and Cystoisospora coccidia, for example. Adult Toxocara canis roundworms can reach 15 cm long. Hookworms are around 0.5–1.5 cm long.

A northern European study published in 2024 included 664 faecal samples from dogs over six months old. Internal parasites were found in 3.5% of these dogs. Roundworm eggs were found in 0.9% in the same study. At one northern European veterinary laboratory in 2025, 28 of 111 canine faecal samples tested for Giardia were positive.

In a northern European sample collected in 2001–2002, intestinal worm eggs were found in 32 of 541 dogs, or 5.9%. Northern hookworm eggs were found in 2.6%. In the study published in 2024, whipworm eggs were found in 0.2%.

Adult whipworms live in the large intestine. Adult hookworms live in the small intestine. Echinococcus canadensis can live in a dog's intestine without visible symptoms.

Causes

Eggs, larvae and intermediate hosts

Dogs can acquire roundworms by swallowing eggs that have become infective in soil. Toxocara canis can pass from mother to puppy through the placenta during pregnancy. Puppies can also acquire it through milk. Infective hookworm larvae can enter through the mouth from the environment. Some hookworm larvae can also penetrate the skin.

Whipworm infection follows swallowing an infective environmental egg. Dipylidium tapeworm is acquired by swallowing an infected flea or chewing louse. Some tapeworms are acquired by eating an intermediate host's tissues or organs.

A rodent eaten by a dog can carry dormant roundworm larvae in its tissues. Ancylostoma caninum hookworm larvae can pass to puppies in maternal milk. Northern hookworm does not pass through milk.

Protozoal transmission

Giardia spreads through cysts passed in faeces. Cysts are infective immediately after defaecation. Faecally contaminated water can transmit Giardia. Cystoisospora's infective stages can survive in the environment for several months.

Canine Cryptosporidium multiplies in the small intestine's surface layer. Its oocysts can be carried in water because they are small and settle slowly.

Cystoisospora oocyst shedding begins around six to ten days after swallowing oocysts.

Risk factors

Toxocara canis is particularly important in puppies, which can acquire many parasites from their mother before birth. First Cystoisospora infection usually occurs during nursing, at three to eight weeks old. Clinical coccidiosis is usually diagnosed at two to four months. Giardia exposure can increase when many dogs live close together in a kennel.

Hunting dogs can acquire tapeworms by eating prey. Eating raw moose or reindeer organs can expose a dog to Echinococcus canadensis. Echinococcus multilocularis is common in Estonia.

Poor hygiene in crowded dog housing can increase faecally transmitted protozoal spread. Cryptosporidium generally causes its most severe symptoms in animals with weakened immunity.

Northern hookworm tolerates cooler climates than Ancylostoma caninum. Young puppies can acquire Cystoisospora from littermates before starting solid food.

Typical symptoms

Diarrhoea characteristics vary with the parasite. Any Giardia symptoms usually begin one to two weeks after infection.

• Intermittent diarrhoea in a puppy with Giardia.
• Strongly foul-smelling flatulence with giardiosis.
• Mucoid, bloody faeces with heavy whipworm infection.
• Roundworms visible in vomit.
• Weight loss with hookworms.
• Itching around the anus from tapeworm segments.

Pale Dipylidium segments around 1 cm long may be visible in hair around the anus. When dry, they resemble rice grains and may be found in bedding.

A puppy with roundworms may gain weight more slowly than expected. The abdomen can appear rounded and swollen. Cryptosporidium can cause watery diarrhoea in puppies.

Roundworm larvae passing through the lungs can make a puppy cough. With Ancylostoma caninum, major intestinal blood loss can cause black, tarry faeces.

Complications and consequences

Ancylostoma caninum feeds on blood from the intestinal lining. Infection acquired through milk can cause sudden, life-threatening anaemia in a young puppy. Northern hookworm, Uncinaria stenocephala, carries a lower anaemia risk.

Severe whipworm infection can lower blood sodium. Coccidiosis can cause severe bloody diarrhoea in puppies. Migrating roundworm larvae can cause pneumonia in puppies. Very heavy Dipylidium infection can obstruct the small intestine.

Rarely, a canine roundworm larva can reach a person's retina and impair vision. In human Echinococcus canadensis infection, a growing larval cyst in an internal organ can impair lung function, for example.

Whipworms attach to the large-intestinal lining and feed on its cells. Protein can leak into the intestine from northern hookworm attachment sites, and blood protein concentration can fall by more than 10%.

Diagnosis at the vet

Looking for different parasites in faeces

The vet asks about lifestyle and possible infection sources as well as symptoms. Flotation uses a suitably concentrated liquid to lift parasite eggs from a faecal sample for microscopy. It can also find Cystoisospora oocysts. Visible segments can be identified by direct microscopic examination.

Tapeworm eggs may be shed only intermittently, so routine egg examination can miss infection. Taenia and Echinococcus eggs cannot be distinguished microscopically. PCR testing of eggs can identify the Echinococcus species. Faeces from three consecutive days can be combined for adult dogs' worm testing because shedding may not occur daily.

Test timing affects results

Hookworms can cause symptoms in young puppies before eggs appear in faeces. Whipworm infection takes around nine to ten weeks to produce egg shedding. Some faecal antigen tests detect whipworms or hookworms before eggs are shed. Giardia can be sought with immunofluorescence testing, for example.

Examining three samples over three to five days helps find Giardia cysts because shedding varies. A Giardia antigen test can be positive even when cysts are not being shed at that moment.

Parasite eggs swallowed in another animal's faeces can pass through a dog's intestine and appear in a sample without the dog being infected. A repeat sample or faecal antigen test can help establish whether eggs are merely passing through.

Whipworm eggs have a lemon-like shape under the microscope. An overly concentrated flotation solution can distort Giardia cysts and hinder identification. Cryptosporidium species can be established with PCR and sequencing when needed. Its oocysts can be only 3–6 micrometres across.

Treatment

Treatment depends on the parasite

The vet prescribes treatment according to the parasite identified or suspected. Praziquantel is used for Dipylidium tapeworm, for example. Treatment also includes flea and chewing-louse control to prevent reinfection. Hookworm susceptibility to medication can vary between species.

A severely anaemic dog with hookworms may need a blood transfusion. Giardia-effective medication is used when infection is found in a dog with diarrhoea. A Giardia finding in a symptom-free pet dog does not usually require medication. In a kennel where many puppies have diarrhoea, treatment of symptom-free Giardia-positive dogs may be considered because of transmission risk.

Finding Cystoisospora in one puppy may lead to treatment of the entire litter because littermates share exposure. Persistent diarrhoea may prompt repeat Giardia testing if no other cause is found. Symptoms continuing after treatment may warrant repeat faecal worm testing.

A symptomatic dog with Cryptosporidium may receive supportive fluids. If kennel worming effectiveness is questioned, faecal testing can check treatment success.

Treatment effectiveness in a dog carrying Echinococcus can be assessed by faecal PCR 7–14 days afterwards. With confirmed infection, the coat can be washed to remove adhering worm eggs. Extensive use of the same medicine in a kennel can favour resistant parasite strains.

Prevention

Picking up faeces reduces environmental parasite eggs. Whipworm eggs can remain infective in soil for years. Cleaning whelping areas and drying surfaces reduce coccidial survival. With Giardia, washable beds and toys can be washed on a cycle of at least 60°C.

Provide clean drinking water and prevent puddle drinking. Preventing access to raw offal reduces Echinococcus exposure. Faecal testing can assess worming needs in a healthy adult with little exposure.

Roundworm eggs become infective in the environment in around two to four weeks. During Giardia infection, washing food and water bowls with hot water helps prevent reinfection.

A dog remaining in a contaminated run can acquire whipworms again from the same soil eggs. Puppies often acquire their first infections very early, so breeders plan parasite control during nursing.

Important for dog owners

Tell the vet about travel, hunting or eating raw organs. Collect a visible worm or segment in a separate container for identification. Before sampling, check whether the laboratory needs a special container or preservative.

Wash hands with soap after picking up faeces. Keep a dog with diarrhoea away from dog parks. Before travelling with your dog, check the destination country's entry requirements through its national veterinary authority.

Ask the breeder for previous worming records when bringing a puppy home. Teach children to wash hands after outdoor play because roundworm eggs in soil can reach the mouth.

Collect faeces as fresh as possible into a clean, tightly sealable container.

Frequently asked questions

Can a dog have intestinal parasites without symptoms?

An adult dog's roundworm infection may be symptom-free despite egg-producing worms in the intestine. A symptom-free dog can also shed Giardia cysts. Giardia testing is not usually needed for a healthy, symptom-free pet dog. Taenia tapeworms also rarely cause noticeable symptoms in dogs.

What could white rice-like pieces in my dog's bed be?

Small rice-like pieces may be dried Dipylidium segments. Segments can also occur in fresh faeces or hair around the anus. Swallowing an infected flea can reinfect the dog.

Does a negative faecal sample rule out worms?

Early in infection, worms may already be present without detectable eggs. Irregular tapeworm egg shedding reduces routine faecal test sensitivity. Testing samples collected on different days can improve detection.

Can canine intestinal parasites infect people?

A person can acquire Toxocara by swallowing soil or food containing infective eggs. Echinococcus canadensis eggs can transfer to hands from an infected dog's coat. The most common Giardia assemblages in dogs are C and D, considered adapted to canids.

Does a healthy adult dog always need a wormer?

A healthy adult with little exposure can be faecally tested and treated according to findings. Tapeworm risk is assessed separately in a dog eating prey or raw organs, because routine sampling can miss eggs. Check trip-specific requirements for the destination country before travelling.