ROUNDWORMS IN DOGS & PUPPIES
TOXOCARA CANIS AND TOXOCARA LEONINA: ROUNDWORMS OF DOGS AND PUPPIES
There are two species of roundworms affecting dogs and puppies: Toxocara canis and Toxascaris leonina. T. 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.
HOW INFECTION OCCURS:
Note: cats cannot be infected with Toxocara canis.
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.
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 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.
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?
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:
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.
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:
Page last updated: 5/31/2016