Could your barky dog have worms? Surprising links between parasites, health and behaviour

You’ve probably heard people talk about the link between pain and behaviour.  But what if I told you that parasites can play a role in those behaviours too?

Worms, fleas, ticks, skin mites and even microscopic organisms like Giardia are not the first thing most guardians think of when their dog’s behaviour changes. But sometimes they can be an important piece of the puzzle.

What behaviour changes might you see?

Every dog is different. There is no one single behaviour or set of behaviours, it is often individual to each dog, but these are some of the signs we see that might suggest it’s sensible to do an up-to-date parasite test:

• Increased agitation or inability to settle
• “Zoomies” or increased scraping after toileting
• Changes in sleep patterns
• Changes in appetite or eating patterns
• Barking more… or becoming quieter and more subdued

But surely you’d see physical symptoms?

Sometimes, but often not — especially in the early stages.

You often can’t tell if a dog has internal parasites just by looking. There are some signs which might be an indicator, such as coat condition, scratching, changes in frequency or consistency of poo, coughing, scooting their bottom on the floor, or changes in weight — but equally, there may be no obvious signs at all in the beginning. And remember those signs can be caused by other things too.

Ticks and fleas are different – there are of course external signs, but you may not see the internal effects straight away (and simply removing the tick doesn’t necessarily remove the risk of disease either). Tick-borne disease is particularly tricky but can have a very significant impact on behaviour as well as physical and emotional wellbeing.

Why parasites can affect behaviour?

If you’ve ever been unlucky enough to have worms (yes, people can pick them up!) you’ll know they can be quite painful — especially when toileting. Dogs are no different.

Parasite burdens don’t just cause local irritation. They can:

• Lead to pain or malaise (for example, hookworms can cause anaemia and gut discomfort (Traversa, 2012)).
• Trigger inflammation in the gut, which changes how well food is digested and absorbed.

And this is backed up by the ever-evolving science

Science spotlight: Parasites and the gut–brain axis

• Dogs naturally infected with Giardia show measurable changes in their gut microbiota compared to uninfected dogs (Kostopoulos et al., 2022).
• Helminths (worms) can reshape both gut bacteria and immune responses across different species (Jenkins et al., 2017) – and there is evolving research in dogs.
• Early studies link certain microbiome patterns with anxiety and aggression in dogs (Mondo et al., 2020)

This means parasites don’t just irritate the gut — they may alter the gut environment in ways that ripple through the immune system and affect mood and behaviour.

Because the gut and brain are closely connected, these changes can spill over into how your dog feels and behaves.

The research is evolving rapidly – in clinical practice, case insights already tell us that this is the case.

Why testing is essential?

Worm/flea/tick prevention measures can help reduce the risk (to varying degrees) but don’t eliminate it completely — and this applies whether you use the chemical sort via your vet or you take a more holistic wellness approach to help make the gut more inhospitable to parasites should they turn up (we discuss the pros and cons of these here – link)

So regular testing is really important (and really, really easy for intestinal and lungworms). Ticks need a slightly different approach – rather than regular testing, you typically only test for tick-borne disease if you know your dog has been exposed and clinical signs emerge, or your dog may have been unknowingly exposed and you have a pattern of symptoms which may fit – and it’s not as easy to spot as you might hope!

That’s why veterinary bodies like the BSAVA recommend a responsible, risk-based approach to parasite control: test first, then treat only when needed (BSAVA, 2021). The WSAVA echoes this globally, advising that parasite care should reflect a dog’s lifestyle and local risks (WSAVA, 2025).

At Canine Thinking, we believe this approach not only protects your dog’s health, but also avoids unnecessary chemicals which can have adverse effects on other aspects of health, can build resistance in some parasite populations (which makes treatment difficult) and is an important part of looking after the environment too.

Ultimately when it comes to choosing your approach to parasites there are lots of pros and cons to consider which we discuss here (link to relevant blog).

The only truly wrong approach is to ignore them completely — it’s a huge risk to your dog, and potentially a risk to you too.

Takeaways

👉 Don’t guess, test!

👉 Sometimes the answer to tricky behaviour lies in the most unexpected places.

👉 If you want to chat about your dog or any concerns, email us at hello@caninethinking.com

References

• BSAVA, BVA & BVZS (2021). Policy position on responsible parasiticide use. British Small Animal Veterinary Association.
• WSAVA (2025). Global Principles of Wellness. World Small Animal Veterinary Association.
• Kostopoulos, I., et al. (2022). ‘Giardia alters the canine gut microbiome’. Frontiers in Veterinary Science, 9:849914.
• Jenkins, T. P., et al. (2017). ‘Helminths and the microbiome: Altered interactions across species’. Frontiers in Microbiology, 8:843.
• Mondo, E., et al. (2020). ‘Gut microbiome composition linked to behaviour traits in dogs’. Scientific Reports, 10:1243.
• Traversa, D. (2012). ‘Hookworm infection in dogs’. Parasites & Vectors, 5:91.