Worm Tales 3: Lungworms

Lungworm

We know of some great animal journeys.

We can watch them on TV. So many weird and wonderful animals pass through so many strange places on Earth. Salmon migrate by leaping upriver; crabs scuttle over the ground; locusts swarm; grazing herds wander; whales go miles and miles using echolocation.

But the journey that I’m going to marvel at today takes place on a much smaller scale. And that’s the journey of a parasite we know as Lungworm.

 

Lungworm is a nematode and it has a posh name: Angiostrongylus vasorum. And just to be confusing, they used to call it French Heartworm, too.

 

So which is its home, the heart or the lungs?

As I said, this one travels a lot. It moves through the dog as it’s growing, like some restless souls travel the Earth, and it spends time on the ground and in other animals too. Perhaps the dogs’ lungworm should be called a no-fixed-abode worm; a wanderer.

 

Where does it start?

That’s a chicken and egg, or a Lungworm and egg sort of question, but the eggs are laid in a dog’s heart.

From the right side of the heart, the eggs move to the pulmonary artery, which is the blood vessel taking oxygen-depleted blood to the lungs. Obviously blood isn’t the only thing it takes there; the egg slips into the airways, which is where the first larval lungworm stage hatches.

Of course having tiny worms in your lungs is enough to make anyone cough. The baby worms wriggle through the lung tissue until some are eventually coughed up into the mouth…

…and then the dog swallows: GULP!

 

What next?

The journey of anything through the gut goes like this: food-pipe, stomach, then long, very wiggly intestine. Finally the baby worms (a bit bigger now) will pop out in the poo and some will eventually be eaten.

 

What by?

Maybe by a dog, and they’ll go round again, but sometimes, crucially, by a mollusc. And in the mollusc they grow a little, sit dormant a little, until such a time as the mollusc gets eaten up by a dog.

 

But molluscs are snails! My dogs don’t eat snails!

Can you be so sure? Dogs eat snails stuck to their play-balls and snails in the soil, or snails that have snuck onto their water or food bowl, or a bone they just happen to fancy chewing. It’s said that silver snail-trails may be infected, too, but that’s not certain. Oh yes, and slugs are molluscs and can carry Lungworm, too. Bizarrely, even frogs can carry the worms (and they aren’t even molluscs).

 

What happens then?

The worm does some growing and changing inside that mollusc and this time when it’s digested by a dog, it doesn’t go straight through.

It burrows through the intestine wall, grows a little bit while it’s there, and then it ends up in the liver.

From the liver it’s not such a great journey along the vena cava (a big vein) to the heart. Our larva is an adult now, and that’s where it lays its eggs.

 

Wow! That’s a fantastic journey!

But not so much for the dog. Developing larvae can cause all manner of problems, and here are just a few:

 

Symptoms of Lungworm

The most common are breathing difficulties and coughing, because of the disruption of tissue of the lungs. They can also cause heart disease, or disruption to blood clotting and therefore random bleeds. Signs of these go from nose-bleeds to superficial bruising, but on a deeper level there can be weakness and collapse. There are also much rarer symptoms caused by migrating larvae getting lost; damage to the brain or the liver or eye.

This means that lungworm related diseases can be difficult to identify. They can also be quite hard to treat. The good news however, is that lungworm is easy to prevent.

 

What can I do?

Talk to your vet. Trying to limit a dog’s ingestion of slugs is quite tricky, but some steps – like taking balls indoors and washing them – can help.

However, a more certain way of prevent lungworm is chemically; there are drugs out there that prevent or kill lungworm and your vet is best placed to advise you about the options.

 

But I’ve kept dogs for years and never had problems with lungworm

When I graduated, I’d never actually seen a case. Lungworm is spreading; more cases are being reported. And it’s possible some cases we now diagnose as lungworm were once just being put down to unexplained ‘sudden death.’

Lungworm goes on an epic journey, which has devastating effects. But veterinary medicine has been on a journey too and now Lungworm’s a disease we can outwit.

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