Roundworm (Round Worms, Round Worm)

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One of the most common parasites found in pets is the roundworm. Often called “ascarids,” there are three types of roundworms (toxascaris leonina, toxocara cati, and toxocaris canis) that are widely distributed in North America and affect cats and dogs. Roundworms are a very important worry to pet owners – rightfully so, as the parasites can also cause disease in humans.

Adult roundworms live in the small intestine of the host, and no matter what type of roundworm your pet has, it can pass millions of eggs into the environment each day. The difference in the various types of roundworms that your pet can have lies in the roundworm life cycle.


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The T. leonina has the simplest life cycle of them all. After a pet ingests roundworm eggs, the eggs hatch and the larvae begin to mature in the small intestine. An adult worm lays eggs which get passed through a pet’s feces. After three to six days, these eggs become infective and animals can become infected after eating something contaminated by the infected feces. Most commonly, mice are the transport hosts of T. leonina. Cats that are out of doors or have been known to catch mice are particularly prone to this form of tapeworm infection.

The T. cati version of roundworm only infects cats. It has a more complicated life cycle than does T. leonina, and is able to very effectively pass from generation to generation. A T. cati infection can be acquired in one of many ways. Often, the first is through an ingestion of eggs. Once the larvae go in the small intestine, they migrate through the circulatory system and can go into the respiratory system or other tissues and organs in the body. Once a roundworm enters body tissues, they become inactive, and can remain that way for months – even years. In kittens, however, the larvae move to the respiratory system, where they are coughed up and swallowed. Once in the stomach, the larvae mature. Much like the simpler T. leonina, the eggs are passed through feces, though they need to remain in the environment for fourteen days before becoming infective. Ingestion of a transport host can also infect a cat with roundworms, as the larvae are released from the transfer host when eaten.

NOTE: This site is dedicated to garden worms and worms found around the environment. We are not a site for information about parasites, we are not doctors, we are bug enthusiasts. This is why we have put together this page of parasite resources for people who are infected with parasites. Please do not ask us to identify a parasite or diagnose a parasite-related issue

The difference in the T. cati roundworm is how it becomes passed through future generations. During the perinatal period, larvae can begin to migrate into the mother’s milk. Kittens can become infected while nursing.

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Four weeks after a cat is infected, the adult roundworm (no matter what type) matures in the animal’s intestine and begins to release the next generation of roundworm eggs.

Just as T. cati in cats, the life cycle of the T. canis roundworm can infect generations of dogs. However, in addition to migrating through a mother’s milk, an infected dog can infect her unborn puppies through what’s known as in-utero transmission. The larvae enter the lungs of a fetal pup, and when the pup is born, the roundworm larvae will be coughed up and swallowed. This method of passing from mother to pup is very common in dogs – that’s why so many puppies have roundworms. They’re born with them!

All roundworm eggs must remain in the environment for days, even weeks, before they become infective. Encysted larvae (inactive larvae in body tissues) can remain dormant for a host’s lifetime.

Roundworms absorb nutrients from the pet in the intestine, where they can interfere with digest and even damage the lining of the intestine. Symptoms of roundworm infestation can often hard to see immediately, as animals with mild infestations can show no signs of disease. Severe infestations come with symptoms such as a pot-bellied appearance, dull coats, even anemia. In young animals, roundworm larvae can even cause pneumonia.

Roundworms can cause a significant health hazard for people. If a human becomes infected (usually by ingesting infective eggs in some way), the larvae migrate through the person’s tissues, usually the liver, lungs, and brain. Roundworm larva can cause inflammation and mechanical damage to organs. A unique form of damage caused by roundworms, most often found in children, can lead to vision loss or even total blindness, as roundworm larvae migrate through the eye.

Good hygiene is extremely important in preventing human infection. Only a trip to a trusted veterinarian can help to decide what form of roundworm an infected pet has, and the proper way to treat the infestation.

Recommended reading (click on the picture for details):
Prevention's Symptom Solver for Dogs & Cats: From Arfs and Arthritis to Whimpers and Worms : An Owner's Cure Finder

Author: The Top Worm

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