Worm Tales, part 1 – Canine Tapeworms

Electron micrograph of tapeworm

Our planet has a wealth of habitats. There are the icy poles; there are equatorial rainforests. There are peat bogs and tundra, mountain and desert, city and moor. Life, however, has developed ways of surviving in almost every nook and cranny, whatever the temperature, light intensity, moisture levels or hazards in that environment.

The animal’s body is another collection of environments with differing levels of harshness, that support small forms of life.

 

One such habitat is the intestine. It’s a long, moist tunnel – or rather a series of smaller moist tunnels joined end to end. The tunnels are slimy and constantly moving; they glisten with juices. The food eaten by their owner is no longer recognisable, having already passed through the stomach, and as it moves along it becomes more mixed up still. Slimy. At a microscopic level, different nutrients pass through the walls into the bloodstream until, at the end of the large intestine, only faeces is left.

Actually, not ONLY faeces. In an animal with a tapeworm, there is something else as well.

 

Dipylidium caninum

But first let’s go back to that intestine  – the small intestine, the first bit. This one belongs to Eric the Schnauzer, who isn’t the sort of dog who would usually eat disgusting things, but he was licking an itchy paw today and accidentally swallowed a flea.

Fleas sometimes contain larvae from a particular tapeworm known as Dipylidium caninum. It’s pronounced ‘dippy-lidd-eee-um K9-um’  – and, sure enough, as the flea is digested in Eric’s small intestine, a larval tapeworm emerges. This is the chance that the lava has been waiting for: it’s a nice warm, moist place with lots of lovely part-digested food and it starts to grow. It grows into an adult tapeworm, with little tapeworm mouthparts, and it then bites into Eric’s intestine and settles there, contented, growing longer and longer. It grows to nearly 20cm and looks like this:

Dipylidium tapeworm
J Walker CC-BY-SA-3.0

Notice those segments. The ones at the end act exactly like miniature seed packets. Eventually they will fall from the end of the tapeworm and be carried along Eric’s gut into the poo. I told you it wasn’t just faeces that came out at this end. The egg packets, by the way, can wriggle. They wriggle out through the anus and go to sit on the dog’s bottom, where they tickle. And dogs, as you know, lick their bums… but they don’t get infected that way! In fact, the lifecycle is not complete until an egg is eaten by a flea larva in the environment.

Once inside a flea, the egg will hatch out and become a larva, and the worm-infested flea will be ready for the cycle to happen again.

But what effect does all this have on Eric? The answer is ‘not much’. It turns out that most dogs do fine with the odd Tapeworm in their guts. In a bad infestation, Eric’s bottom might get very itchy from tapeworm egg sacks and if you look closely, you might sometimes spot little white specks moving around the skin outside his anus.

But there are exceptions: puppies have baby immune systems and are quite small. They have been known to suffer serious intestinal blockages caused by tapeworms. In any dog, a tapeworm that has been attached to the intestine for some time might let go, and the dog might vomit an entire worm back up.

And what about people? Can a person pick up Eric’s Dipylidium babies? Yes. They do have to consume a flea, but it has been known…..

 

Taenia

The word taenia come from the Greek for ribbon, bandage or stripe and there over 100 taenia tapeworm breeds. A few of them involve dogs. For example: Taenia ovis infects sheep and goats but uses dogs as an intermediate host. Taenia hydatigena infect dogs, but pigs and sheep are their intermediate host.

An intermediate host is one that the tapeworm uses in its development. Here’s an example.

Animal One does a poo containing tapeworm eggs. Some of these crawl away from the poo and eventually are eaten by Animal Two, the intermediate host. If Animal Two is the correct intermediate host for the species, the eggs will hatch and the baby worms will wriggle their way to a certain part of their new host’s anatomy  – for instance, a muscle – and remain there, as a cyst. Taenia play the long game. Their intermediate host will eventually die. And then they get eaten by another Animal One (which is why it is important for Animal One to be very careful when eating raw meat).

The raw meat of the intermediate host must be consumed by the main host in order for the cycle to perpetuate. Luckily, Eric the Schnauzer doesn’t get raw meat very much. But he might pick up Taenia pisiformis, if he manages to find a dead rabbit.

 

Echinococcus

Adult worms live in a dog; the eggs pass out in poo. A sheep eats the grass with dog poo on it. Larvae may live in the sheep’s body for years. They form cysts, for instance in the eye or liver or lung of the intermediate hosts. They grow extremely slowly and may never cause the sheep a problem, particularly as sheep are slaughtered young for lamb.

However, if Eric were to eat the sheep raw – in particular the liver or lungs, where the cysts often form – he would become infected. If a human actually ingests the eggs in dog-poo, the human might end up with tapeworm cysts forming inside them……

Hydatid Cyst
Ekmirajkar CC-BY-SA-3.0

There were 10 cases of Echinococcus in humans in England and Wales last year.

 

So. Do I need to treat my dog for tapeworm?

The risks of serious disease to dogs from UK Tapeworms are quite low, but blockage in the intestine can be life threatening, especially in pups. Other problems include itchy bottoms, lethargy and unexpected weight-loss. As well as worming your dog, treating for fleas is a good idea, as fleas are needed for the worm to be passed on.

 

However, the main reason for routinely worming against tapeworm is to protect humans  – and in particular, children. And other people’s children, because one should never underestimate how easy it is for a child to accidentally eat your dog’s poo.

 

Is this the only reason I worm my dog every month?

No, that’s only the beginning. Make sure you continue to follow this blog carefully, because some other glorious wormy beasties will feature soon.

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