What are roundworms?
Roundworms (also known as nematodes or ascarids) are parasites that live freely in the intestine, feeding on partially digested intestinal contents. Their name comes from their tubular or “round” shape. Roundworms are the most common gastrointestinal worm found in dogs and can also be transmitted to people.
How do dogs get roundworm?
A dog is infected when it ingests roundworm eggs in the environment. These eggs may come from the feces of infected dogs or from the tissues of an accidental (intermediate) host, such as an earthworm, cockroach, rodent, or bird.
The eggs hatch in the dog’s gastrointestinal tract, and immature worms (larvae) migrate through the muscles, liver, and lungs. After several weeks, the larvae return to the intestine to mature into adults. When the adult worms begin to reproduce, eggs pass into the dog’s stool, completing the parasite’s life cycle.
During their migration, some roundworm larvae may become enclosed in a cyst in the tissue of the host’s body. In a female dog, these encysted larvae can come out of the cyst during pregnancy and cross the placenta into an unborn puppy. Puppies can be born with roundworms and can pass fertile eggs in their stools by the time they are about 11 days old.
Roundworm larvae may also enter the mother’s mammary glands and be passed to the puppies through the milk (trans-mammary infection) during nursing. Dogs are usually affected by roundworms as puppies.
Are roundworms dangerous to my dog?
Roundworms are most dangerous to puppies, and the most common consequence is stunted growth. Roundworms eat partially digested food in the intestinal tract, so if they are present in large numbers, they rob the growing puppy of vital nutrients. Roundworms can complete their life cycle in immature dogs, but as the puppy’s immune system matures (usually by six months of age), the roundworm’s larval stages become enclosed in a cyst in the puppy’s muscles. They can remain encysted in the dog’s tissues for months or years.
Roundworm larvae swallowed by adult dogs usually encyst in the dog’s tissues, with very few maturing into adults in the dog’s bowel. As a result, very few eggs are passed in the stool, leading to difficulty in diagnosis and treatment.
In an intact female dog, encysted larvae can resume development after estrus (heat), and she can shed eggs in her stool at that time. In spayed dogs, a roundworm infection may indicate that an underlying immune system disease has allowed the encysted larvae to complete their life cycle.
What are the clinical signs of roundworm infection?
Adult dogs may have no signs of roundworms or they may have mild signs, such as soft stool and vomiting. However, large numbers of roundworms may cause life-threatening problems in puppies and debilitated or older dogs.
In puppies, common clinical signs include a pot-bellied appearance, abdominal discomfort, depressed appetite, dull coat, vomiting, diarrhea, poor growth, coughing, and seizures (rare). You may notice adult roundworms in your dog’s stool or, rarely, in their vomit.
How is a roundworm infection diagnosed?
To diagnose roundworm infection, a small amount of the dog’s stool is examined under a microscope (fecal flotation). The distinctive eggs are easily recognized under the microscope.
Roundworm eggs are usually plentiful, but in some cases, it may take more than one fecal examination to find them. Your veterinarian may also run a routine PCR screen on your dog’s feces that detects small amounts of parasite DNA to identify roundworm and other parasite infections even before the worms start to shed eggs.
What is the treatment for roundworm infection?
Treatment is simple and effective. There are many safe and effective deworming medications available to kill adult roundworms in the intestine. Some of these medications kill only the adult worms and do not affect migrating or encysting larvae, so at least two or three treatments are needed. Many heartworm preventives are effective against intestinal roundworms and help prevent future infections (e.g., Heartgard® Plus, Interceptor® Plus, Simparica® Trio, Nexgard® Spectra, and Advantage® Multi).
Ideally, puppies are dewormed at each booster vaccine appointment. Nursing dogs should be treated at the same time as their puppies. Your veterinarian will advise you on the best treatment and prevention plan for your pet.
What is the prognosis for a dog diagnosed with roundworm infection?
The prognosis for a roundworm infection is good if appropriate medication is given promptly. However, in some instances, extremely debilitated puppies may die.
How can I prevent a roundworm infection in my dog?
Prevention of roundworm infection should include the following measures:
- Deworm pregnant dogs after six weeks of pregnancy to reduce the risk of environmental contamination or transmission from the mother to her puppies.
- Deworm puppies routinely, starting at about two weeks of age, and repeating every two weeks for four treatments. Your veterinarian will recommend the most appropriate deworming schedule.
- Use a heartworm preventive that is effective against roundworms to stop the shedding of eggs into the environment. Talk to your veterinarian about the best options for your dog.
- Control the population of insects and rodents, as they are sources of roundworm infection for dogs.
- Properly dispose of pet feces, especially from yards and playgrounds. Roundworm eggs may remain viable in the environment for long periods.
Are roundworms dangerous to people?
Roundworms can be a health risk for humans. The most common source of human infection is soil contaminated with cat or dog feces. As many as 10,000 cases of roundworm infection in humans have been reported in one year in the United States. Children are at an increased risk for health problems if they are infected.
Humans are like any other accidental host. If a person swallows infectious eggs, the larvae can invade the tissues and become encysted in various organs. If a young child ingests a large number of eggs, clinical disease may become apparent. Very rarely, liver problems may result from roundworm larval migration. Even less commonly, the larvae can migrate into the eye and cause blindness.
In suitable environments, the eggs may remain infectious to humans and dogs for years. It is important to wash your hands thoroughly after playing with your pet or after being in areas where they may have defecated (such as playgrounds or sandboxes). Strict hygiene is especially important for children. Do not allow children to play in potentially contaminated environments. Be mindful of the risk posed by public parks and uncovered sandboxes. Roundworm eggs may be present even if feces are not visible.
