« Worms in dogs » | This article presents pet owners with 10 species owners should know. It explains how worms affect dogs and, in some occasions, their owners. Diseases that can be passed to humans by animals are called zoonoses. They represent serious matter of concern for public health. Thus, it is important for pet owners to be aware of the existence of such conditions and understand how to prevent such diseases in pets (and people).
- This blog is intended as a source of general information for pet owners. It does not constitute specific veterinary advice towards a particular medical case. If you are concerned with a particular aspect of your pet’s health, please, book a video appointment to talk with a qualified veterinarian.
Worms in dogs: Roundworms
Roundworm is a common name for a category of worms called Nematodes. They are called this way because of their thread-like appearance. Many different parasitic species of worms in dogs belong to this category. The section below, introduces several roundworms that may be of interest to dog owners; or to people interacting with dogs.
Heartworms and lungworms
Species 1: Dirofilaria immitis / Dirofilaria repens (zoonose)
Those worms are also known as filarial nematodes. They are found in many areas of southern Europe such as Spain, Greece, Italy, South of France. They are transmitted by certain species of mosquitoes.
Dogs who do not live in these countries can potentially acquire Dirofilaria immitis whilst travelling on a holiday with their owners. Dirofilaria immitis is known to cause heartworm disease in dogs and may occasionally infect humans. Antiparasites products are available to help prevent heartworm disease in dogs.
Dirofilaria repens is responsible for a skin problem in dogs, where the adult worm is found living under the skin. The larval stage, called microfilariae, circulates in the blood stream. Since microfilariae are present in the blood, mosquitoes can pick them up during a blood meal and pass them to other individuals, where it may grow into an adult worm.
In infected humans, Dirofilaria repens remains in its immature form and is well-known for a condition called human Dirofilariosis. It causes the apparition of nodules under the skin and a syndrome called larva migrans, where the eyes may become infected. This condition can be treated both medically and surgically (removal of the worm).
In the first half of the 2000s, parasitologists became concerned after cases of dirofilariosis with Dirofilaria repens were, for example, found in Germany in several hunting dogs (2004) and in a few others, hosted at a kennel in the Berlin area (2007). Those dogs had not travelled outside of Germany, neither they had been imported into the country.
Consequently, it was understood that Dirofilaria repens was starting to become an « emergent pathogen » through dissemination of mosquitoes from southern to northern Europe, but also through increase travels of dogs in endemic areas. Antiparasites medicines are designed to prevent and treat Dirofilaria repens infection in dogs (major reservoir), which in turn lowers the probability for mosquitoes to pass it to humans.
Species 2: Angiostrongylus vasorum
Angiostrongylus vasorum is a worm which has gained increasing attention due to its spread across geographies worldwide. This worm is transmitted to dogs via the random ingestion of snails or slugs. Historically, A. vasorum is known as the « French heartworm » because it was first observed in this country.
This worm is responsible for a potentially fatal disease in dogs infected with it. Symptoms will vary from no particular observable signs to life-threatening respiratory and neurological problems, as well as bleeding.
Thankfully, antiparasites products allow to prevent this worm from threatening dogs’ lives. Veterinarians are also in a position to detect the presence of Angiostrongylus vasorum with a rapid test kit, directly performed at the veterinary clinic.
Other means of testing require either more time or resources and are potentially more invasive for the dog: faecal sample analysis (Baermann test) or PCR test performed on the fluid collected from a bronchoalveolar lavage.
A study performed in Belgium (2016) aimed at understanding the extent to which A. vasorum was spread amongst the canine population in the southern part of the country. Results revealed that A. vasorum was present in dogs who would not show any symptoms. Therefore, those dogs represent a risk, since they would keep releasing larval stages in their faeces and maintain the life-cycle of the worm active.
Additionally, the study recommended to be mindful of those dogs who tend to pick up and eat random things, such as slugs or snails, in areas where the worm is known to be present. Those dogs should be monitored and receive adequate preventive treatment.
Species 3: Crenosoma vulpis
Crenosoma vulpis is another type of lungworms known to infect the respiratory system of red foxes, dogs and badgers. The worm is encountered across geographies such as Europe and North America.
Researchers are still studying the distribution of C. vulpis across geographies, however it is now known that a snail called Cornu aspersum also called common garden snail, might represent a « suitable intermediate host of C. vulpis ».
Sepcies 4: Eucoleus bohemi (Capillari boehmi)
Eucoleus bohemi is a worm infecting nasal cavities of dogs and wild species such as foxes. This worm is often misdiagnosed whereas infected animals show symptoms such as nose bleed, sneezing, coughing and a loss of their ability to smell.
Literature on the topic reports some challenge in correctly diagnosing and treating this parasitic infection, even whit antiparasite treatments.
Hence, research currently suggests a strategy based upon a combination of actions owners may take:
- Preventing their dogs from eating faeces
- Regularly carrying faecal samples
- Keeping up to date with antiparasite treatments
Species 5: Spirocerca lupi
Spirocercosis is a potentially deadly disease affecting dogs who swallow the intermediate hosts of this endoparasite, such as a beetle or lizards, birds or rodents.
After ingestion, the larvae of Spirocerca lupi is released from its host into the dog’s stomach and will start to migrate to its final destination, the wall of the oesophagus, via blood vessels. Once there, it is able to reproduce and release eggs.
This has consequences for the dog because the parasite forms nodules in the oesophagus, leading to symptoms such as regurgitation, vomiting, esophagitis, gastric reflux as well as a wealth of serious complication, including sudden death.
Furthermore, in 8 to 26% of cases, those nodules have a potential to turn into a type of cancer called sarcoma. In its malignant form, spirocercosis is treated by surgical removal of nodules and chemotherapy. However, the outcome remaining poor, it is expected that detection of those nodules and their removal happen before they reach a malignant stage.
Early detection of the parasitic disease in its benign form allows for medical treatment of the dog with the relevant protocol.
In 2019, an article published in the Vet Record (online), gave an account of a diagnosed case of spirocercosis found in the UK in a 2 year old female crossbreed dog who had been imported from Hungary 4 months prior presentation to a university vet hospital.
The dog unfortunately passed away 2 days after undergoing surgery for resection of the nodule lodged into her stomach, which nodules was filled with Spirocerca lupi worms.
Species 6: Thelazia callipaeda (zoonose)
The larvae of T. callipaeda is transmitted to both humans and animals by fruitflies who land in the conjunctiva of those hosts.
Initially a condition reported in Asian countries, it is now increasingly noticed in Europe, affecting both cats and dogs, as well as wild species such as foxes.
The infection can be transmitted to humans, especially in countries of southern Europe: France, Spain, Switzerland and Italy but also in eastern european countries.
The symptoms observed are as reported in literature: « ocular pruritus, lacrimation, congestion and discharge, epiphora, exudative conjunctivitis, corneal edema to keratitis and corneal ulceration in severe cases. »
The treatment involves removing the worms manually and providing antiparasite medicines in the category of macrocyclic lactones.
Species 7: Ancylostoma caninum / Uncinaria stenocephala
This condition is also known as ancylostomiasis and gather species of roundworms such as Ancylostoma caninum and Uncinaria stenocephala. They live in the small intestine of dogs and are referred to as « voracious blood-sucking adults and fourth stage larvae » in textbooks.
As a result, dogs infested with those worms will suffer blood loss, manifested by anemia, and enteritis. The infection with the larval stage of the worms happens either by direct ingestion or through penetration of the skin.
More specifically, Ancylostoma caninum is transmitted to puppies feeding colostrum from their mother. There is a potential for cutaneous larvae migrans in humans (zoonose) with the species called Ancylostoma brasilensis, which also affect pets.
Diagnosis is made either via necropsy of the pups who have died in the litter or via faecal sample analysis (egg identification).
For animals exhibiting acute symptoms, treatment consists of supportive care depending on the severity of the situation, as well as administering antiparasite medication. In all other cases, prevention and treatment with the relevant antiparasite treatment is indicated.
Species 8: Trichuris vulpis
The condition is also called trichuriasis with the whipworms infecting the caecum of dogs. Dogs contaminate themselves by ingesting feces contaminated with eggs of T. vulpis. It is worth noting that eggs can remain in the environment for months to years.
Following contamination, the symptoms can be inexistent to severe, including diarrhea which might contain fresh blood, dehydration, anemia and weight loss.
Diagnosis is made with a faecal sample analysis and the condition can be treated with antiparasite medication.
Trichuris trichiuria is the whipworm infecting humans. There is no substantial evidence that T. vulpis can be passed to humans.
Ascarid worm infection
Species 9: Toxocara canis (zoonose) / Toxascaris leonina
The disease is also known as toxocariasis and concerns the infestation of dogs with small round worms. Young puppies and pregnant bitches are most likely affected. Puppies usually acquire the worms from their mother ( transplacental transmission). Adult dogs seldom show symptoms, although they can contaminate themselves by ingesting feces or an intermediate host of the parasite, a rat for example. It is worth noting that T. canis infects dogs whereas T. leonina can infect both cats and dogs.
Worms belonging to the Toxocara genera are responsible for zoonotic diseases as they can transfer to humans via ingestions of eggs from contaminated places. Ingestion, especially by children, may result in cases of larva migrans (visceral and ocular) but also may lead to intestinal obstruction when the load of worms in intestines becomes important.
Infested puppies will either show no signs or a pot-bellied appearance, which might prompt to investigate the matter further. Infestation might be accompanied by signs such as vomiting or diarrhea with or without presence of visible worms.
Eggs are known to be resistant in the environment and hard to totally destroy, even with chemicals. Since the potential for zoonose is known, it is recommended that pet owners deworm their young pets with the appropriate antiparasite treatment. Pets can re-infect themselves with increase risk to contaminate humans, especially children and immunosuppressed individuals. Therefore, it is important for pet owners to keep pets up to date with antiparasite treatments.
Worms in dogs: Tapeworms
Tapeworms represent a category of flat parasitic worms. They can infect many different species of animals. The section below informs on one of the disease some of them can cause in dogs.
Species 10: Mesocestoides lineatus / Mesocestoides corti (potential zoonose)
Dogs contaminate themselves with the stage 3 of the larval form, called a tetrathyridia. This larval stage is present in the small preys dogs may hunt and ingest, such as snakes, birds and some categories of small mammals.
Once ingested, the tetrathyridia will develop into the adult worm within the intestines. However, in some occasions, the larvae may migrate in other organs (liver, lungs, subcutaneous tissues) and trigger some symptoms such as anorexia, breathing difficulties and abdominal distension accompanied by an inflammatory response leading to ascites and pleural effusion (fluids in chest and abdomen).
The treatment is based on administration of antiparasite medication and attempts to remove the parasites by lavage. However, in some occasions, the parasites may never disappear and signs will come back.
Further source of information and readings
- Extensive information on Dirofilariosis can be found here (2018)
- Lempereur, L., Martinelle, L., Marechal, F. et al. Prevalence of Angiostrongylus vasorum in southern Belgium, a coprological and serological survey. Parasites Vectors 9, 533 (2016)
- Colella, V., Mutafchiev, Y., Cavalera, M.A. et al. Development of Crenosoma vulpis in the common garden snail Cornu aspersum: implications for epidemiological studies. Parasites Vectors 9, 208 (2016)
- Traversa, D., Di Cesare, A. & Conboy, G. Canine and feline cardiopulmonary parasitic nematodes in Europe: emerging and underestimated. Parasites Vectors 3, 62 (2010)
- Nina Gillis-Germitsch, Stefan Müller, Francesca Gori, Manuela Schnyder, Capillaria boehmi (syn. Eucoleus boehmi): Challenging treatment of a rarely diagnosed nasal nematode in dogs and high prevalence in Swiss foxes, Veterinary Parasitology, Volume 281, 2020
- Segev, G., Rojas, A., Lavy, E. et al. Evaluation of a spot-on imidacloprid-moxidectin formulation (Advocate®) for the treatment of naturally occurring esophageal spirocercosis in dogs: a double-blinded, placebo-controlled study. Parasites Vectors 11, 127 (2018)
- Otranto, D., Dantas-Torres, F. Transmission of the eyeworm Thelazia callipaeda: between fantasy and reality. Parasites Vectors 8, 273 (2015)
- Vieira, L., Rodrigues, F.T., Costa, Á. et al. First report of canine ocular thelaziosis by Thelazia callipaeda in Portugal. Parasites Vectors 5, 124 (2012)
- Jimenez Castro, P.D., Howell, S.B., Schaefer, J.J. et al. Multiple drug resistance in the canine hookworm Ancylostoma caninum: an emerging threat?. Parasites Vectors 12, 576 (2019)
- Traversa, D. Are we paying too much attention to cardio-pulmonary nematodes and neglecting old-fashioned worms like Trichuris vulpis?. Parasites Vectors 4, 32 (2011)
- Heneberg, P., Georgiev, B.B., Sitko, J. et al. Massive infection of a song thrush by Mesocestoides sp. (Cestoda) tetrathyridia that genetically match acephalic metacestodes causing lethal peritoneal larval cestodiasis in domesticated mammals. Parasites Vectors 12, 230 (2019)