Nematodes are the most abundant animals on Earth (according the Encyclopaedia Britannica)   Trees have them; soil has them; the insides of animals have them….. And so, of course, do people and their pets.


But what exactly is a nematode?

Nematodes are Roundworms. These are round worms, as their name suggests: earthworms are the obvious example. The Encyclopaedia Britannica describes roundworms as being ‘the most abundant animals on Earth’; they have an opening at each end, and soil, tissue and dirt travel through them, getting smaller as the worm breaks this matter down and removes some useful nutrients. It is an important part of the decay process.


And how do nematodes affect me?

They help to shape our landscapes and support the food chain. Without nematodes, our world would look completely different……



And what?


Is any of this directly relevant to my pet?

Well actually, yes. There is a point to all this….


Toxocara Canis, by Jana Bulantová

Meet Toxocara canis, one of the more unsavoury nematodes. The adult can measure up to 18cm, and hangs out in cats and dogs’ intestines.



Yikes indeed, especially if you are a puppy. Tangles of worms stuck in tiny intestines can lead to blocked intestines, which can – in bad cases – lead to death.


Ugh! So what are they doing there?

Wriggling. Surviving. Here’s the life-cycle.

Firstly, a dog eats poo. Some dogs do this quite happily, uninvited; others do so by a more subtle method, such as licking an infected dog’s bottom or eating something off the floor that just happens to be infected, or accidentally getting some poo on their pads and licking it off later. This sort of thing probably happens more often than you think it does.

Secondly, the teeny eggs that have been hiding in the poo hatch out in the dog’s intestine.

What hatches out is a larva (parasitologists like to call these L1 forms) which will burrow through the wall of the intestine, until they find a particular blood vessel. Blood vessels are handy transport systems – not just for oxygen and nutrients, but also for larvae, which hitch a lift in the blood to the lungs.

The larvae burrow around in the lungs for a little while, making the dog cough. When the dog coughs, the larvae are brought back up into the mouth….. And swallowed. Bigger and older now, the larvae form cysts in the intestine wall.

Some of the dogs that now have cysts in their intestines will be female, and will get pregnant. The larvae then ‘wake up’ and infect the milk or the womb directly, until they end up inside a pup.

In the puppy’s intestine, the adult worm hatches out and lays eggs, which pass through the intestines and into the poo….and the cycle begins again.


That sounds complicated

More so than I’m making it sound, because sometimes another animal – a rabbit, say – eats the fragments of poo with the eggs in. The eggs hatch and the larvae wriggle and close themselves off in cysts within this other animal (the intermediate host). A dog (or fox, maybe) then comes along and eats the rabbit…. and the cysts wake up and infect the milk or the womb of the dog… and so on.


How Clever!

Yes. For little things without much of a brain, nematodes’ journeys are absolutely epic.


Do they cause much damage?

Toxocara can kill its host – particularly when there are very heavy infestations inside puppies and the intestines become blocked.

The movement of larvae around the body can lead to fatigue, abdominal pain and swelling, weight loss, vomiting, poor coat and an utter failure to thrive.

What’s more, people catch the disease too. If an L1 hatches in the human gut, it tends to travel to the eye and cause a cyst…..


So it’s true about dog-worms causing blindness in people?

Exactly! Toxocariasis from dogs, cats or foxes can actually migrate to various organs, and therefore cause a range of symptoms, including coughs, fevers, stomach pains, fitting, liver disease, and eye damage leading to blindness. It is luckily quite rare, but it happens.


So what do I, as a parent, need to do?

If you are a parent, it is desperately important that your children don’t eat dog-poo or cat-poo. Bear in mind that contaminated material isn’t always as obvious as it sounds. If a cat defecated in a golf bunker or child’s sandpit and buried the evidence, worm larvae might not be noticed. The sand may still be infected months to years later, too. This is why looking for poo does not rule out any roundworms; why it is advisable that kid’s sandpits have a lid; why careful hand washing should be supervised after sandy play; and why such play-areas no longer allow dogs. Cats, meanwhile, are harder to ban and they do love a sandy toilet…

It really is important for their kids to wash their hands.


And as a pet-owner?

Properly worm your pet!


Do I have to given them a tablet?

Not these days! Tablet wormers can often be given by a nurse at your practice; or substituted for liquids, or a paste, or for drops. Speak to the staff at your practice about the array of products available: in the past where there were one or two main products, now most practices stock lots.


Are there other roundworms in dogs and cats?

Yes; and in cattle, sheep, goats and chickens and frogs. Nematodes are everywhere, each with their own particular private lives. In general, however, the rules are simple regarding all parasites; Worm your animals; wash your hands.