Canine roundworms, or ascarids, are internal parasites. They live in the small intestines, swimming about freely, feasting on partially digested food and reproducing at rapid rates. Roundworms are subject to specific life cycles that require adult worms live within a host. Adult roundworms can't thrive or reproduce in feces, soil, water or any other outside medium.
Two species of roundworms -- Toxascaris leonina and Toxocara canis -- infect dogs and puppies. Although adult worms can't live outside the host, once their eggs are expelled into the environment via host feces, the eggs can remain viable for months to years. Fresh feces isn't infective, as it takes approximately four weeks for the larvae within the eggs to become infectious. Dogs become infected with Toxocara canis in four ways: By consuming infected soil, by consuming an infected rodent, bird or insect, by nursing from an infected mother or during embryonic development in an infected mother. Dogs are infected by Toxascaris leonina in two ways: By consuming infected soil or water or by consuming an infected animal or insect.
The Roundworm's Life Cycle
Roundworm eggs are shed into the environment when an infected animal defecates. Once the feces decomposes, the surrounding soil and water is infected with eggs. Inside the dog, the eggs hatch, and the larvae emerge and mature into adult worms. Adult roundworms settle in the dog's small intestines. Female roundworms lay eggs, which are shed into the environment via feces, and the life cycle begins all over again. Occasionally, an adult worm may be passed via feces or vomit, but this worm will not reproduce or even survive for long outside of its host.
The Effects of Infection
Roundworm infections typically present with vomiting, diarrhea, abdominal swelling, colic, lethargy, coughing, gagging, weakness, mucous feces, abdominal pain and a dull coat. If the infestation is allowed to proceed unchecked, it can give rise to serious conditions, such as enteritis (intestinal inflammation), weight loss, pneumonia, and intestinal obstruction or rupture. Roundworm infections are most dangerous to puppies due to their fragile systems. Heavy infestations can be fatal.
Treatment and Prevention
There are many highly effective medications available to treat roundworm infections. Common active ingredients include fenbendazole, milbemycin oxime, moxidectin, febantel, selamectin, pyrantel and piperazine. Of course, prevention is always better than having to resort to treatment. Puppies under three months old should be routinely dewormed with a safe, age-appropriate preventative every two to three weeks, beginning at two to three weeks of age. Prevention in older puppies and adult dogs is easy. You can either periodically administer a dewormer, or use a monthly heartworm preventative that also contains a deworming ingredient.