Toxocariasis is a parasitic infection caused by roundworms that affects dogs and cats. Toxocara canis and Toxascaris leonina are the roundworms that can infect dogs. Although they are identical parasites, they operate differently in dogs’ bodies, causing slightly different ailments. Toxocariasis and toxascariasis are caused by them. Toxascaris leonina infections are frequently referred to as toxocariasis in the scientific literature.

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Both of these diseases are frequently referred to as roundworm in dogs, despite the fact that there are other forms of roundworm parasites that can infect dogs. 

Roundworm species in dogs

All roundworms in dogs are nematodes, so named because they belong to the phylum Nematoda. Toxocara canis and Toxascaris leonina are members of the Ascarididae family, also known as ascarids. Our connected post will teach you more about Toxocara canis in dogs.

There are several genera of roundworms that can harm animals. Ascaris, Baylisascaris, Hexametra, and Parascaris are among them. Ascaris lumbricoides is the most often known to infect dogs, particularly puppies. 


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Toxocara canis is a kind of canis.

Toxascaris leonina is a kind of toxascaris.

Toxocara canis is a kind of canis.

It is a big intestinal nematode and one of the most frequent parasites in dogs‘ intestines. Adults range in size from 4-6″ (10-15 cm). They can infect dogs of any age, but puppies are particularly vulnerable.

Adult roundworm infections are found in the small intestine, where they lay eggs that are then removed with feces. The eggs, once in the environment, become a source of infection for other canines. The eggs hatch in the small intestine after being consumed, resulting in the release of larvae. When Toxocara larvae are released, they might migrate in four different ways in the dog’s body:

Toxocara canis larvae travel through the intestinal wall, to the lungs, and then back to the gut via entero-pneumo-enteric migration. It is there that the cycle is completed when they reach adulthood. This migration occurs in dogs who become infected before the age of 5 weeks.

Entero-pneumo-somatic migration: Similar to the previous type, this migration begins in the colon and progresses to the lungs. The larvae, on the other hand, travel throughout the organism from the lungs. They infect a variety of tissues, including the muscles, liver, kidney, uterus, and mammary glands. This migration occurs in dogs who become infected after the age of 5 weeks.

Hepato-pneumo-enteric migration happens in pups when they are infected transplacentally, that is, while still in the mother’s uterus. The larvae in the mother’s tissues are transferred to the pups via the maternal-fetal circulation. They migrate to the liver in the fetus, then to the lungs, and lastly to the gut.

The entero-enteric cycle is not a migration in and of itself because the parasites are only present in the intestine. This type of migration happens when dogs become infected through the intake of paratenic hosts (such as rodents, birds, or invertebrates) or the lactogenic pathway (in puppies who swallow milk from infected moms).

Toxascaris leonina is a kind of toxascaris.

It, too, is an intestinal nematode, however the adult worms are slightly smaller than Toxocara. They often range in size from 1.1-4″ (3-10 cm). The parasite does not migrate organically. The cycle is called as the entero-enteric cycle because it occurs solely in the intestine. The global infection rate of dogs is roughly 2.9%, but in the Eastern Mediterranean, it may be as high as 7.0%. 

Can roundworm in dogs be passed on to humans?

Toxocara canis larvae can infest people. They can infect humans and produce the disease visceral larva migrans. This infectious disease is distinguished by the formation of granulomatous lesions in many organs, most notably the liver, lungs, brain, and, on rare occasions, the eye. It is accompanied by symptoms such as intermittent fever, chronic cough, weight loss, and loss of appetite.


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It primarily affects children under the age of five. They are frequently infected by ingesting dirt contaminated with these parasites’ eggs. However, it is a worldwide public health issue, and infection can occur at any age.

The prevention of this human-transmissible dog disease is dependent on a few basic steps:

Keep dogs away from parks and playgrounds for children.

Maintain a proper deworming routine in dogs from birth.

Avoid having close contact with dogs who have not had effective parasitological control.

Roundworm causes in dogs

Toxocariasis in dogs is caused by an infestation of the Toxocara canis roundworm. However, transmission routes can differ. Toxocara canis most typically infects dogs via the four primary methods listed below:

Eating soil, dung, and other stuff in the dog’s environment that contains embryonated eggs is an example of direct egg ingestion. Read our article on why dogs eat excrement to learn more about coprophagia in dogs.

Ingestion of paratenic hosts: Dogs may consume larvae-infested rodents, birds, or invertebrates.

Parasites are transmitted to fetuses via the transplacental pathway while in the maternal uterus. In this situation, the puppies are contaminated from birth.

Lactogenic pathway: Roundworms are transmitted to pups via milk from their mothers while they suckle on their teats.

Toxascaris leonina infection can occur only through two pathways:

Consumption of embryonic eggs

Intake of paratenic hosts

This means that transmission of Toxascaris cannot occur directly from the mother to her offspring.

Roundworm symptoms in dogs

Now that we understand how Toxocara canis is spread in dogs, we can examine the resulting symptoms in the dog’s body. The severity of the symptoms can vary depending on factors such as the degree of the infection, the dog’s overall health, and the path of migration inside the body.

Dogs with roundworms frequently exhibit the following symptoms:

Growth has been slowed.

appearance deterioration

swollen abdomen



In both Toxocara and Toxascaris infections, the most common symptoms in dogs are vomiting and diarrhea. This is due to the parasite’s presence in the stomach and intestine. 

Adult parasites are shed with feces and vomit on a regular basis, but the latter is less prevalent. As a result, roundworms can be found in dog excrement.

It is usual for pneumonia to develop during the lung migration phase in the case of Toxocara canis. Coughing, nasal discharge, and an increase in respiratory rate accompany this.

Death can occur during both the pulmonary and intestinal phases. This is caused by intestinal rupture and the resulting peritonitis. In general, diseases are more severe when animals are grown in filthy conditions, as well as in people who have weakened immune or nutritional state.

The photo below shows an example of a Toxocara canis round worm.

Roundworm treatment for dogs

Roundworm treatment necessitates the removal of Toxocara canis and Toxascaris leonina roundworms from the animal’s body. The deworming technique for roundworms will be determined by the animals’ age and physiological state:

Puppies must be dewormed every two weeks beginning at two weeks of age. This medication should be continued every two weeks until two weeks following weaning. Following that, it must be dewormed monthly until it is 6 months old.

Pregnant pigs should be treated with macrocyclic lactones between days 40 and 55 of gestation, or with fenbendazole between days 40 and postpartum. Learn more about Panacur for dogs in our guide.

Lactating females should be treated every two weeks, along with their puppies.

Adult dogs: it is best to examine each animal’s risk separately in order to choose the most effective deworming program. The normal suggestion is to perform treatments at least four times a year, while in high-risk scenarios (such as dogs living with children), monthly deworming is recommended. Periodic stool tests can be performed as an alternative to conventional deworming and treated if the result is positive.

If you find roundworms in your dog’s excrement but no other symptoms, you should still deworm the dog. If an infestation is allowed to spread, it can be lethal. This is especially true when roundworms have made their way into the tissues of important organs.