About Roundworm
Roundworms, also known as ascarids, are large, heavy-bodied worms that grow up to six inches in length. The roundworms in Canada that commonly infect dogs are Toxocara Canis , (probably the most common dog worm in the world) and Toxascaris Leonina .
Puppies are the most common victims of roundworm infection. In fact, researchers currently estimate that 95% of the puppies born in the United States are infected with roundworm and a similar percentage is likely in Canada. By the time the puppy is six months old, most of the adult worms are expelled by the dogs natural defense mechanism. However, a relatively large proportion of adult dogs continue to have light infections without the knowledge of the owner.
The infection often occurs as larvae that have been "dormant" in an adult female, are reactivated by the mothers pregnancy. These larvae, plus any newly ingested eggs, migrate via the placenta to the liver of the fetus. The larvae also migrate to the mammary glands of the mother, where new-born puppies become infected when they nurse. Older dogs can get worms by eating an animal that is already infected (such as a mouse). There is no prenatal infection with T. Leonina . Dogs only become infected with this roundworm by ingesting eggs directly or via consumption of an intermediate host.
T. canis can be a serious health problem for human children. The infection in children, called visceral larva migrans, can cause fever, pneumonitis and sometimes, encephalitis. The larvae can also invade the eye (ocular larva migrans), disturbing vision. Common preventive measures include frequent hand washing, and preventing expectant mothers from "stoop and scooping" and from cleaning litter boxes.
Life Cycle
The life cycle of the roundworm is complex because infection and migration of the worms occurs in a variety of ways. An animal can become infected by ingesting eggs directly or by eating an infected animal.
1. Mature roundworms in small intestine.
2. Adult lays eggs.
3. Eggs in feces.
4. Larvae develop inside eggs.
5a. Dog ingests infective eggs.
5b. In pregnant dog, larvae may pass to fetus. Larvae migrate up trachea, are swallowed, and mature in pup's small intestine.
In puppies less than 3 months old, the roundworm larvae work their way to the liver, then burrow through the diaphragm to reach the lungs. From there, they find their way through the air passages until they are coughed up and swallowed. The time period from infection to adult is approximately 27 days . Most researchers believe adult worms live an average of 4 months. Most are expelled before the dog is 6 months old by the dogs natural defense mechanism.
In older puppies and dogs, larvae tend to migrate though the soft tissues as opposed to following the air passages. The larvae can be found in the dog's organs as early as 8 days after infection from the environment.
Clinical Signs
The effects of roundworm depend on the age of the dog and the number, location and stage of development of the worms. Older dogs usually are not seriously affected because they have very few adult worms. However, puppies may die, especially if they are in highly contaminated environments. Circumstances of death usually include acute pneumonia and severe diarrhea. Puppies from severely infected mothers may be stillborn. In less severe cases, there may be a "pot-bellied" appearance, intermittent diarrhea, occasional vomiting, and possibly anemia. A dog also may be restless and exhibit twitching, or even have convulsions.
Diagnostic Options
In adult dogs, roundworm infection can be diagnosed by fecal flotation, direct smear and sedimentation, as well as finding live worms in the stool or vomit. In puppies, the diagnosis is more difficult because roundworm eggs are not produced before a pup is 4 weeks old. Even after 4 weeks, the number of eggs produced is relatively low and stool samples are not very reliable. Up to 50% of the test results may indicate a false negative result. These tests combined with clinical symptoms indicate the presence of roundworm to the veterinarian.
Treatment
Treatment and control for roundworm currently includes Milbemycin Oxime found in both Sentinel and Interceptor. Both of these products offered by Novartis Animal Health are GUARANTEED to remove the adult worms with each monthly dose. (For more information on these products and their mode of action please follow the links) Depending on the situation and environment your dog is in, your veterinarian will be able to prescribe the appropriate medication to treat your dog for these parasites.
Under ideal conditions, roundworm eggs may survive on the ground for months, and a treatment of the dogs environment may be needed in severe, persistent cases. It is important to note that all canine dewormers currently available are labeled as being effective only against the adult stage of the worm. Within days of deworming, immature larvae that were present in the gut, but unaffected by the medication, may develop into mature adults and begin laying eggs again. Re-infestation from the environment can result in larvae beginning their migration to the lungs in as little as 8 days. Although it is possible to see eggs on a fecal examination, regular monthly doses of INTERCEPTOR or SENTINEL are GUARANTEED to wipe out the new adults at the time of each dosing. The worms will not be able to establish themselves in a significant way within the pet, and the dog will not show clinical symptoms of roundworm disease.
Prevention
As in human medicine, veterinary medicine is shifting its focus from the treatment of diseases and symptoms, to the prevention of them before they have a chance to harm your pet. In the same way that vaccines prevent your pet from developing formerly common diseases, it is now an accepted practice to include deworming medication at regular intervals, to keep your pet healthy and free of parasites. Many dogs in Canada are treated with monthly heartworm medication such as Interceptor and Sentinel. The active ingredient in these products is also effective in removing intestinal parasites from your dog with each dose, keeping your dog happy, healthy and parasite free all season long.
