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Roundworms, or ascarids, are the most common intestinal parasites that affect cats and dogs. The three species of ascarids that afflict these house pets include: Toxocara canis in dogs, Toxocara cati in cats, and Toxoscaris leonina in both cats and dogs. These parasites can also be found in wild carnivores. The roundworm is a cylindrical white worm that can reach one to eight inches in length. The worm lives freely in the intestinal tract. Roundworms will on occasion be vomited up by the pet, or passed in a bowel movement. A diagnosis is usually made by having the pet’s stool specimen checked by your veterinarian.

Signs and Symptoms

Pets that have an infestation of roundworms can exhibit a wide range of clinical signs. Some of the more common symptoms include: vomiting, diarrhea, poor weight gain or a loss of weight, dull hair coat, a “pot bellied” appearance, blood in the stool, restlessness, coughing and passing gas from the rectum. This parasite can cause stunted growth, anemia, central nervous system disorders, pneumonia, and disturbances in digestion. Many animals harbor roundworms and show no clinical signs of having this intestinal parasite.

Parasite Life Cycle 

Roundworm infection can occur in the fetal stage of development, by nursing from the mother, from contact with contaminated soil, and by eating rodents or small vermin that serve as transport hosts. A pet may harbor the larval stages of the roundworm in the body tissues for several months or years. The dormant larval stages can develop at any time in the pet’s life. The hormonal changes that occur in the mother dog or cat can cause an activation of these encysted ascarids and they can pass to the developing puppy or kitten. The adult roundworm can be found in the intestinal tract as early as the second week of life. The developing worm begins to shed eggs 23 to 40 days after the birth of the affected animal. The roundworm egg in the soil undergoes developmental changes depending on the environmental conditions of temperature and humidity. An intermediate host such as a rodent may pick up the roundworm larvae at this stage. A pet can become infected by ingesting this intermediate host. Dogs and cats can also obtain roundworm through contact with contaminated ground, or through grooming fur that has been soiled with fecal material containing the eggs. Once the infective roundworm larva enters the pet, it migrates through the body, and its path can include the liver, lungs, bloodstream, kidneys, muscles, and nervous system. The roundworm can encyst in these organs and halt its development or it can continue on to become an adult worm. Some pets may develop an immunity to roundworm infection. The ascarid egg is infective for several months in the soil. Ground that has been polluted with ascarid eggs may serve as a reservoir for repeat infections for a pet. The ascarid egg can withstand extreme temperatures of heat and freezing. Eggs can be killed by drying the soil, or through exposure to heat greater than 98 degrees Fahrenheit. Drying the soil is the best method for inactivating the ascarid egg.  

Public Health

Roundworms can also infect humans. The parasite causes a disease known as visceral larvae migrans. In humans, a developing larval stage of the roundworm migrates through various body organs after the egg has been ingested. The disease is usually seen in young children who have been handling animal wastes, or playing in soils contaminated with ascarid eggs. All pets should be handled using proper hygiene to prevent transmission of this disease. Animal wastes should be disposed of properly and pets should be prohibited from soiling public grounds.

Treatment and Prevention

Several medications are available that can effectively remove roundworm infection from your pet. All worm medications should be prescribed by your veterinarian, because many drugs can be poisonous if not properly administered. When a pet needs to be treated for roundworms, a second dose of medication is usually administered. This second treatment is given to remove any parasites that were in the larval stages at the time of the first worming. Dogs and cats used for breeding should be checked for parasites prior to breeding. Stool samples should be checked on all adult dogs and cats every six months as part of their regular health program. Puppies and kittens should have their stool specimens checked each time they visit the veterinarian for their initial series of vaccinations. It is also recommended to have samples checked when a pet suffers from an intestinal upset.
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