Tilly, a 12 week old Jack Russell Terrier puppy had a swollen belly

The new puppy seemed very healthy, but Isabelle’s mother had noticed that she had a pot belly. She asked me about it when Tilly was brought in for her first vaccination. The most common cause of a swollen abdomen in young puppies is simple: roundworms. The dog roundworm, known officially as ‘Toxocara canis’,.can affect dogs of all ages, but is most common in puppies. The worm can, very rarely, be passed on to children, where, in exceptional cases, it can cause blindness. The good news is that the roundworm is very simple to control.

It is important to understand the life cycle of the roundworm. When a female puppy is infected with roundworms, some of the young worms (so-called ‘larvae’) move through the wall of the intestine into the blood. They settle into muscles and other parts of the body where they form indestructible cysts. If the female puppy becomes pregnant later in life, those hidden young worm larvae become activated, and move back into the bloodstream. They can then cross over into any unborn pups in her womb. In addition, some young worms cross over in the mother’s milk to the suckling newborn animals.

In young puppies, adult worms gather in the intestines, where they look alarmingly like pieces of spaghetti, measuring 3 – 5 inches long. They produce microscopic eggs that are passed in the faeces. These eggs are harmless at first, but once they have incubated in the open air for a few weeks, they can become infectious to other dogs, and also sometimes to humans.  The risk to humans is not from handling puppies, but from touching soil that has been contaminated by puppies several weeks previously.

So how can humans interrupt this devious worm life cycle? All puppies should be given repeated worming treatments from an early age, and adult dogs should also be wormed regularly. In addition, “poop scooping” should be part of the routine of keeping puppies and dogs, so that any worm eggs are removed from the environment before they have time to develop. As an extra precaution, children should always wash their hands before meals, to minimise any risk of worm eggs passing from dirty hands into mouths. Puppies should be wormed from two weeks of age, every two weeks until they are twelve weeks old, and then once a month until they are six months of age. Adult dogs should be wormed every three months throughout their entire lives.

In the past, breeders used traditional remedies to de-worm puppies. I heard a elderly farmer recently describe how he used to force a wad of chewing tobacco down the throat of young puppies. The nicotine in tobacco would certainly kill the worms, but the farmer admitted that the nicotine also killed some of the puppies! Other old fashioned remedies included laxatives and purgatives, which literally caused the intestines to be washed out.

Modern de-worming drugs are much more effective, and much more gentle, with no side effects. A range of products is available, including tablets and liquid medicines. You can even buy a “spot-on” dog wormer that is dripped from a vial onto the skin between the shoulder blades. The product is absorbed through the skin into the animal’s bloodstream. In addition to providing a de-worming dose that lasts for a month, the product also protects the animal against fleas and other parasites.

Science is continually developing new and better ways to deal with common problems like parasites. Ask your vet if you want to learn more about the most modern products, since the newest and best products are generally released through vets before reaching the mass market. I gave Tilly a worm dose at the same time as her vaccination, and I also gave her owners enough worming medication to last until she is six months old. A week later, Tilly’s pot belly had disappeared, and she had become a slim, trim, terrier puppy.


  • Dog worms can rarely cause illness in children, and dog owners need to take action to prevent this
  • All puppies should be given regular worm doses from an early age
  • All adult dogs should be given an effective wormer every three months.

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Please note that I am unable to answer veterinary questions in comments. If you have questions or concerns about your pet's health it is always better to contact your vet.

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