Dogs pick up lungworm by swallowing slugs and snails, or the slime they leave on grass, toys and water bowls. The result is a parasite that lives in the airways and blood vessels of the lungs. A persistent cough, reduced stamina or unusual bruising in a dog who mouths things in the garden is worth investigating rather than treating as a cold.
Why the autumn rain matters
Slugs and snails need moisture and cool temperatures to be active. Through a dry Vancouver August they stay hidden under pots, logs and decking. As soon as the rain returns in late August and September, they come out in numbers, at dusk and overnight, exactly across the lawns and paths where dogs sniff in the morning.
South Vancouver gardens are good habitat. Shaded side yards, raised beds, compost bins, the damp strip behind a fence and the mulch around ornamental beds all hold moisture well into the day. A dog who patrols the garden first thing in the morning meets the previous night’s traffic.
Most owners have never been told this is a route of infection at all, which is why it goes unconsidered for so long. Dogs are rarely seen eating a slug. The more usual story is a dog who picks up a ball that has been lying on wet grass, drinks from an outdoor bowl left out overnight, or chews a stick from a damp flower bed.
What lungworm actually does
Lungworm is a group of parasites rather than a single organism, and the species differ in where they settle and how much harm they cause. In general terms, larvae swallowed by a dog migrate from the gut to the chest, mature in the airways or in the blood vessels serving the lungs, and shed larvae that are coughed up, swallowed and passed in the faeces. Slugs and snails then pick those up, and the cycle repeats.
The consequences fall into two groups. Airway forms cause persistent inflammation and a chronic cough that does not settle. Vascular forms live in the vessels of the lungs and can additionally interfere with normal blood clotting, which is where the more serious complications come from.
Prevalence differs a great deal between regions of Canada, and the species that matters most in one province may be uncommon in another. That is genuinely a question for your veterinary team rather than for an article, because it shapes both the testing and the prevention advice you should be given.
The cough that is not kennel cough
The signs develop slowly, which is why lungworm is so often missed or mistaken for something else:
- A cough that persists for weeks and does not follow a boarding or daycare stay
- Reduced stamina, or a dog who stops earlier on walks than they used to
- Faster breathing at rest, or breathing that looks like more work than usual
- Weight loss or a gradual decline in condition
- Poor appetite and general dullness
- Bleeding that seems out of proportion: bruising, prolonged bleeding from a small cut, nosebleeds, or blood in the stool
- In some cases, unexplained wobbliness or seizures
The bleeding signs are the ones to take most seriously, because they indicate a clotting problem rather than simply an irritated airway. A dog who bruises easily or bleeds unexpectedly needs assessment promptly, and our emergency veterinary services are available around the clock for exactly that kind of concern.
A chronic cough gets attributed to kennel cough, allergies or age far more often than it gets investigated. If a cough has lasted more than a couple of weeks, has not responded to what has already been tried, or has appeared in a dog with no exposure to other dogs, lungworm belongs on the list of things to rule out.
Cats have their own version
Cats can carry a lungworm of their own, usually picked up by hunting rather than by mouthing garden objects, often through eating birds, rodents or amphibians that have themselves eaten an infected snail. Outdoor and hunting cats are the ones at risk.
Affected cats tend to show intermittent coughing, wheezing or increased breathing effort. Because those signs overlap closely with feline airway disease, a coughing cat needs proper investigation rather than an assumption in either direction, and a faecal test is part of that work-up.
How it is diagnosed
Diagnosis is not always straightforward, because larvae are shed intermittently and a single faecal sample can easily come back negative in an infected animal. Samples collected over several consecutive days are often requested for that reason, and a specific technique is used rather than a standard faecal float.
Chest imaging shows the changes in the lungs and helps distinguish this from other causes of a chronic cough. Bloodwork is used to look at inflammation and, where a vascular form is suspected, at clotting. Some species can be identified with a specific blood test. All of this runs through our diagnostic services, and the results are interpreted together during a medical consultation.
Prevention is where the useful part is
The single most important thing to understand is that not every routine parasite product covers lungworm. Many popular treatments target intestinal worms, fleas and ticks without addressing this group at all, so a dog can be entirely up to date and still be unprotected. Ask specifically. It is a reasonable and useful question, and the answer depends on your dog’s lifestyle and where you live.
Alongside the right product, a few practical habits reduce exposure:
- Bring toys, chews and water bowls indoors overnight rather than leaving them on the grass
- Refresh outdoor water rather than topping it up
- Pick up faeces promptly, which breaks the cycle for every dog using that space
- Discourage stick chewing and drinking from puddles on damp mornings
- Reduce slug habitat near where your dog spends time by clearing damp piles of leaves and debris
- Avoid slug pellets entirely where pets have access, since some are dangerously toxic in their own right
A parasite plan is worth reviewing every autumn rather than setting once, and that review fits naturally into our wellness program. Our article on parasite problems unique to Vancouver covers the wider local picture, and parasite prevention in South Vancouver explains how the seasons shift the risks. For a different lung parasite that is spread by mosquitoes rather than slugs, our guide to heartworm in dogs is a useful comparison.
When to get in touch
Book an appointment for a cough lasting more than a week or two, for a drop in exercise tolerance, for unexplained weight loss, or if your dog is a known slug and snail eater and you would like their prevention reviewed. Treat it as urgent if there is bleeding that will not stop, unusual bruising, laboured breathing, collapse or a seizure.
Frequently asked questions
How do dogs get lungworm?
By swallowing slugs or snails, or the slime trails they leave behind. Most dogs are never seen eating one. The common routes are picking up a ball or chew left on wet grass, drinking from an outdoor bowl left out overnight, or mouthing sticks and plants in a damp garden. Puppies and dogs who chew everything are at higher risk.
Does regular deworming protect against lungworm?
Not necessarily. Many routine parasite products cover intestinal worms, fleas and ticks without covering lungworm, so a dog can be fully up to date and still unprotected. Ask your veterinary team specifically whether your dog’s current product covers it, and let them know how much time your dog spends nosing around a damp garden.
Is lungworm contagious to other dogs or to people?
It does not pass directly from dog to dog. The parasite needs slugs or snails to complete its life cycle, so an infected dog spreads it only by passing larvae in faeces that those molluscs then eat. That is why prompt faeces pick-up genuinely helps. The species involved are not considered a human health risk in the way some other parasites are.
My dog has been coughing for weeks. Could this be it?
It is worth ruling out, particularly if the cough has not followed contact with other dogs, has lasted more than a couple of weeks, or has not improved with what has already been tried. Several conditions cause a chronic cough and they are managed differently, so the useful step is investigation rather than another round of guessing.
Why would a lung parasite cause bleeding?
Some species live in the blood vessels serving the lungs rather than in the airways, and they can interfere with normal clotting. That is why bruising, nosebleeds, prolonged bleeding from small wounds or blood in the stool are treated as serious signs in this context, and why they warrant same-day attention rather than a routine appointment.
Can I just use slug pellets to remove the slugs?
Please do not, where pets have any access. Some slug baits are severely toxic to dogs and cats and cause tremors and seizures, so you would be trading one hazard for a faster acting one. Reduce damp hiding places instead, bring toys and bowls in overnight, and speak to your veterinary team about appropriate preventive treatment.