Mar Vista Animal Medical Center

3850 Grand View Blvd.
Los Angeles, CA 90066

(310)391-6741

www.marvistavet.com

ROUNDWORMS IN DOGS & PUPPIES

 
(Photocredit: Morguefile.com)

 

TOXOCARA CANIS AND TOXOCARA LEONINA: ROUNDWORMS OF DOGS AND PUPPIES

There are two species of roundworms affecting dogs and puppies: Toxocara canis and Toxascaris leoninaT. leonina can infect both dogs and cats so identifying this roundworm might be helpful in indicating which pets in the household are at risk for further contagion; however, both worms respond to the same treatment protocol so more specific identification beyond "roundworm infection" frequently is not made.

 

TOXOCARA CANIS

HOW INFECTION OCCURS:

In dogs, there are four ways by which infection with Toxocara canis occurs:

  • Consuming infective worm eggs from soil in the environment (generally through normal grooming).
  • Nursing from an infected mother dog.
  • Consuming a prey animal (usually rodent) that is carrying developing worms.
  • During embryonic development when an infected mother dog is pregnant (most puppies are infected this way).

Adult Toxocara canis worms
(Photocredit: Flukeman via Wikimedia Commons)

 

Note: cats cannot be infected with Toxocara canis

 

WORMS THEMSELVES ARE NOT DIRECTLY CONTAGIOUS TO PEOPLE OR TO ANIMALS.
FRESH FECES DOES NOT CONTAIN THE INFECTIOUS STAGE OF T. canis.
WORM EGGS REQUIRE 30 DAYS TO BECOME INFECTIOUS WHICH MEANS IT IS
CONTAMINATED DIRT THAT IS INFECTIOUS TO PEOPLE AND ANIMALS.

LIFE AS A ROUNDWORM:

Toxocara canis has one of the most amazing life cycle in the animal kingdom. It is crucial to understand this life cycle if effective treatment is to be pursued.

(Photocredit for fresh egg: Joel Mills via Wikimedia Commons; Photocredit for developed egg: Flukeman via Wikimedia Commons; all the rest: original graphics by marvistavet.com)

STEP ONE: Toxocara eggs are passed in the host’s feces. If a fecal sample is tested, the eggs can be detected but the eggs are too young to infect a new host at this stage; the worm embryo within the egg must develop for a month or so before it becomes able to establish infection in a new host. During this time of worm egg development, the feces has melted into the environmental soil and is no longer evident; the worm eggs are loose in the garden (or other environmental) dirt. If environmental conditions are favorable, it takes about a month for the egg to become infective but Toxocara eggs are famous for weathering harsh environmental conditions. Eggs can remain infective for months to years.

Note: Fresh feces is not infectious. Soil contaminated with feces is infectious.

STEP TWO: The egg containing what is called a “second stage larva” is picked up from the dirt by a dog or by some other animal. usually in the course of normal self-grooming. The egg hatches in the new host’s intestinal tract and the young worm burrows its way out of the intestinal tract to encyst in the host’s other body tissues. If the new host is a dog, the life cycle proceeds. If the new host is a member of another species, the larvae wait encysted until the new host is eaten by a dog.

(original graphic by marvistavet.com) (original graphic by marvistavet.com)

STEP THREE: These second stage larvae can remain encysted happily for years. If the host is a dog, the larvae mostly encyst in the host’s liver. When the time comes to move on, the larvae excyst and migrate to the host’s lungs where they develop into “third stage larvae.” They burrow into the small airways and travel upward towards the host’s throat. A heavy infection can produce a serious pneumonia. When they get to the upper airways, their presence generates coughing. The worms are coughed up into the host’s throat where they are swallowed thus entering the intestinal tract for the second time in their development. 

If the host is pregnant, the larvae do not migrate to the lung after they excyst; instead they home to the uterus and infect the unborn puppies. The second stage larvae make their way to the puppies’ lungs to develop into third stage larvae.

If the host is a nursing mother, second stage larvae can migrate to the mammary gland instead of the lung after excysting. Puppies can be infected by drinking their mother’s milk, though, due to the intrauterine cycle described above, the litter would probably already be infected.

(original graphic by marvistavet.com)

 

Note: When dogs are dewormed with traditional dewormers, this affects only worms in the intestinal tract. It does not affect encysted larvae. It is very difficult to prevent mother to puppy transmission and routine deworming is not adequate. It is possible to prevent infection in unborn puppies by using a specific daily protocol of fenbendazole or with an off-label protocol of ivermectin. There is no FDA approved protocol for killing encysted roundworms in dogs/preventing infection in unborn puppies so discuss these protocols with your veterinarian.

 

STEP FOUR: Once back in the intestine, the larvae complete their maturation and begin to mate. The first eggs are laid about one week after the fourth stage larvae have arrived in the intestine and about 4-5 weeks after infection has first occurred. From here the cycle repeats.

 

WHY IS INFECTION BAD?

Roundworm infection can have numerous negative effects. It is a common cause of diarrhea in young animals and can cause vomiting as well. Sometimes the worms themselves are vomited up which can be alarming as they can be quite large with females reaching lengths of up to seven inches. The worms consume the host’s food and can lead to unthriftiness and a classical “pot-bellied” appearance. Very heavy infections can lead to pneumonia as the worms migrate and, if there are enough worms, the intestine can actually become obstructed.

It should also be noted that human infection by this parasite is especially serious (see below). It is important to minimize the contamination of environmental soil with the feces of infected animals so as to reduce the exposure hazard to both humans and other animals.

 

HOW DO WE KNOW IF OUR DOG IS INFECTED?

You may not know and this is one of the arguments in favor of regular deworming. Regular deworming is especially recommended for dogs that hunt and might consume the flesh of hosts carrying worm larvae. Puppies are frequently simply assumed to be infected and automatically dewormed.

Of course, there are ways to find out if your dog is infected. If a dog or puppy vomits up a worm, there is a good chance this is a roundworm (especially in a puppy). Roundworms are long, white and described as looking like spaghetti. Tapeworms can also be vomited up but these are flat and obviously segmented. If you are not sure what type of worm you are seeing, bring it to your vet’s office for identification.

Toxocara egg

Fecal testing for worm eggs is a must for puppies and a good idea for adult dogs having their annual check up. The Companion Animal Parasite Council recommends fecal testing 2-4 times during a puppy's first year of life and once or twice a year after that. Obviously, if there are worms present, they must be laying eggs in order to be detected but, by and large, fecal testing is a reliable method of detection.

 

HOW DO WE GET RID OF ROUNDWORMS?

Numerous deworming products are effective. Some are over the counter and some are prescription. Many flea control and/or heartworm prevention products provide a monthly deworming which is especially helpful in minimizing environmental contamination. Common active ingredients include:

  • Febantel (active ingredient in Drontal plus)
  • Pyrantel pamoate (active ingredient in Drontal, Strongid, Nemex, HeartgardPlus and others)
  • Piperazine (active ingredient in many over the counter products)
  • Fenbendazole (active ingredient in Panacur)
  • Milbemycin Oxime (active ingredient of Sentinel and Trifexis.)
  • Moxidectin (active ingredient in AdvantageMulti)

There are two important concepts to keep in mind about deworming. Medications essentially anesthetize the worm so that it lets go of its grip on the host intestine and passes with the stool. Once it has been passed, it cannot survive in the environment and dies.

This means that you will likely see the worms when they pass so be prepared as they can be quite long and may still be alive and moving when you see them.

The other concept stems from the fact that all the larvae in migration cannot be killed by any of these products. After the worms are cleared from the intestine, they will be replaced by new worms completing their migration. This means that a second, and sometimes even a third deworming is needed to keep the intestine clear. The follow-up deworming is generally given several weeks following the first deworming to allow for migrating worms to arrive in the intestine where they are vulnerable.

Do not forget your follow-up deworming.

 

TOXASCARIS LEONINA

WHAT ABOUT TOXASCARIS LEONINA?

The life cycle of Toxascaris leonina is not nearly as complicated. T. leonine does not migrate through the body in the way that Toxocara does. Instead, the fresh egg is passed by the host in feces, develops into an infectious embryo in the environment, and is swallowed by the new host. The Toxascaris egg develops much faster and can be ready for its new host as soon as one week from the time it was passed. Once inside the host, however, Toxascaris development becomes slower. The young worm lives in the host intestine without migrating through the body and becomes a mature worm in 2-3 months. Like Toxocara, Toxascaris can be picked up by wildlife and the canine or feline host can be infected through hunting and consuming prey.

Fresh egg from Toxascaris leonine
(Photocredit: Joel Mills via Wikimedia Commons)

 

(Photocredit for fresh egg: Joel Mills via Wikimedia Commons; Photocredit for developed egg: Flukeman via Wikimedia Commons; all the rest: original graphics by marvistavet.com)

Note: Toxascaris leonina can infect both dogs and cats alike.

FOR MORE INFORMATION:

The Companion Animal Parasite Council has put up educational sites for dog owners on roundworms at:

www.petsandparasites.org/dog-owners/roundworms

www.capcvet.org/capc-recommendations/ascarid-roundworm/


(Photocredit: Morguefile.com)

Roundworms in Cats & Kittens


(Photocredit: U.S. Fish and Wildlife Service)

Roundworms in Humans

 Page last updated: 5/31/2016