Understanding Toxocariasis & Toxoplasmosis

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  • 0:01 Parasites
  • 0:50 The Roundworm
  • 3:05 Toxoplasmosis
  • 4:58 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will go over two famous parasites that can cause zoonotic disease and serious, albeit rare, problems in humans, which are toxocariasis and toxoplasmosis.


Animals, including household pets, can sometimes be chock full of parasites, organisms who derive a benefit from a host but give nothing beneficial back in return. The host is the animal who harbors these parasites. And the benefits the parasite derives can be everything from food to shelter.

Maybe you have a parasitic friend or family member who seems to fit that description. But the parasites in this lesson are probably a bit more dangerous than that. These parasites are the monsters inside and outside your pets. Some of them do not affect humans at all, and others can cause horrific damage to us.

This lesson will cover two types of zoonotic parasitic diseases called toxocariasis and toxoplasmosis. A zoonotic disease is a disease that can be transmitted from an animal to a human.

The Roundworm

We'll start off with one of the most horrifying ones at first. It looks like a strand of spaghetti, but it shouldn't end up on your plate as a result. You wouldn't want to eat this thing, or more precisely, the eggs it produces.

What is this monster inside your pet? It is the roundworm, a parasitic worm that causes toxocariasis, an infectious disease caused by roundworms of the genus Toxocara.

Now, I need to be clear about something. 'Roundworm' is a term that's commonly used in science to refer to any kind of nematode, an organism from the phylum Nematoda. Ascarids, hookworms, whipworms, and strongyles are all nematodes and thus they are all, in a way, roundworms as a consequence.

But more often than not, in veterinary medicine specifically, when we say the word 'roundworm,' we are talking about a specific kind of nematode, one from the order of Ascaridida, the ascarids.

And why wouldn't you want to eat this parasite's eggs? Well, it's because there's a chance it can cause permanent eye damage, including blindness, especially in children.

Roundworms live in the intestines of many animals, dogs and cats included. They produce eggs that are then expelled when an infected animal defecates. The feces then contaminate places like a yard, sandbox, and so forth, and the eggs become infective over time.

When children go outside to play, and as children inevitably do, put dirty things in their mouth, the eggs are swallowed, hatch inside the child, and move from the intestines, into the liver, then the lungs, and then spread to other places, like the brain, heart, and eyes, after which it can cause vision loss and even death in rare cases.

Roundworm eggs are extremely hardy. There is no known chemical that can kill them in the environment. This means it's critical that people with pets ensure they pick up after their pets right after they do their business, consult with their veterinarian as to any necessary treatments for the animal, and watch their kids closely to make sure they don't put dirty hands and objects into their mouth.

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