Lungworm in dogs — symptoms, UK prevalence, and why Biheldon doesn't cover it

Quick answer. Lungworm (Angiostrongylus vasorum) is a parasitic nematode transmitted to dogs through ingestion of slugs, snails, or contaminated grass/water. It lives in the heart and pulmonary arteries — not the gut — and can be fatal: case-fatality rates run 2–13% even with veterinary treatment. Biheldon does not cover lungworm. Drontal Dog does not cover lungworm. Panacur does not cover lungworm. Effective UK prevention requires a monthly prescription product containing milbemycin oxime (Milbemax, Nexgard Spectra) or moxidectin (Advocate, Bravecto Plus). If you see persistent cough, breathing difficulty, unexplained bleeding, or unusual lethargy, see a vet immediately — these are red flags, not “wait for the next dose” symptoms.

If you searched for “lung worm dog symptoms”, you’re probably worried about a specific dog. This guide is written from that starting point: what the symptoms actually look like, what to do about them, what UK prevalence looks like in 2026, and what to buy if you want to prevent lungworm rather than treat it. We’re going to be honest about one thing up front: the wormer we sell does not treat lungworm. Biheldon covers tapeworm, roundworm, and hookworm — the intestinal parasites. Lungworm is a different problem and needs a different product.

What lungworm actually is

Angiostrongylus vasorum is a nematode (roundworm) that, despite the common name, doesn’t live in the gut. Adult worms live in the right side of the heart and the pulmonary arteries — the blood vessels that carry blood from the heart to the lungs. They lay eggs that hatch into first-stage larvae (L1), which migrate through the lungs into the airways, get coughed up, swallowed, and passed out in the dog’s faeces.

Slugs, snails, and certain frogs eat the larvae from contaminated grass or faeces. Inside the slug or snail, the larvae develop into infective third-stage larvae (L3). Dogs become infected when they eat a slug or snail — either deliberately (some dogs find them appetising), accidentally (a slug on a chew toy left in the garden overnight; one in the water bowl), or incidentally (chasing and crunching a slug while playing). Drinking from puddles or grass where slug or snail mucus has been deposited can also transmit infective larvae.

This lifecycle matters because it tells you where the risk actually is: not in dog parks, but in any garden or outdoor space where slugs and snails are present. Which is most UK gardens.

UK prevalence in 2026

A. vasorum was first reported in UK dogs in the 1970s, initially in pocket hotspots in the south-east and south-west of England. It has spread substantially since:

• Fox-reservoir prevalence rose from 7.3% in 2005 to 18.3% in 2014 in UK wild red foxes (Taylor et al. 2015)
• Current geographic spread covers south-east England, the midlands, south Wales, and as far north as Glasgow
• Endemic hotspots are south-east England, the west midlands, and south Wales
• Case-fatality rate is 2–13% even with veterinary treatment — this is one of the more serious UK canine parasites

The Elanco “Be Lungworm Aware” map is a useful — though commercially-sponsored — interactive reference for postcode-level case reporting. Your own vet will usually have the most accurate picture of how common lungworm is in your immediate area, because they see the actual case load.

Symptoms — what to watch for

Lungworm symptoms in dogs fall into three clusters depending on which body system is most affected. A single dog may show symptoms from one cluster or several at once.

Respiratory symptoms (most common)

• Persistent dry cough, particularly worse after exercise
• Increased breathing effort or breathing rate at rest
• Reduced exercise tolerance — the dog tires faster than usual
• Wheezing or noisy breathing

Bleeding / clotting symptoms

Lungworm interferes with the dog’s blood-clotting cascade, which can produce unexplained bleeding:

• Bruising on the skin or visible mucous membranes with no obvious injury
• Bleeding from the gums, nose, or eyes
• Prolonged bleeding from a minor wound or after a routine procedure (nail clip, vaccination)
• Blood in the urine or stool

Systemic / neurological symptoms

• Lethargy or unusual quietness lasting more than 24 hours
• Loss of appetite
• Weight loss in a previously healthy dog
• Seizures or behavioural changes (rarer, but possible with neurological involvement)
• Sudden collapse

Any of the bleeding-symptom cluster should be treated as a vet emergency — not a “make an appointment for next week” situation. Lungworm-associated coagulopathy can deteriorate fast.

Why a 3-monthly intestinal wormer doesn’t cover it

Praziquantel and pyrantel embonate (the actives in Biheldon and Drontal Cat) work on intestinal worms — they paralyse the worms in the gut and the dog passes them out. Lungworm doesn’t live in the gut. The adult worms live in the heart and pulmonary arteries, and the larvae live in the lung tissue and airways. Praziquantel doesn’t reach those tissues at clinically meaningful concentrations, and pyrantel embonate is barely absorbed from the gut at all (which is its safety advantage, but also its lungworm-coverage disadvantage).

Even febantel — the third active in Drontal Dog Tasty Bone — doesn’t cover lungworm. Febantel extends Drontal’s spectrum to whipworm, not lungworm. The fenbendazole in Panacur has off-label activity against Oslerus osleri (a less common UK lungworm) but not against Angiostrongylus vasorum.

The only drug class with reliable, licensed A. vasorum activity is the macrocyclic lactones: milbemycin oxime, moxidectin, and (less commonly) selamectin. These work systemically — they’re absorbed from the gut (or skin, in spot-on form) and reach the heart and lung tissues at concentrations high enough to kill the parasites at multiple lifecycle stages.

What actually works against lungworm

In UK practice, these are the products with licensed lungworm activity:

All of these are prescription-only in the UK — they require a vet consultation and a written prescription. The treatment protocol for an active lungworm infection (as opposed to monthly prevention) usually involves four weekly doses of Milbemax or a dedicated moxidectin protocol; your vet will set this depending on the dog’s clinical picture.

For ongoing prevention in endemic areas, monthly Milbemax or monthly Advocate are the standard choices. Both also cover intestinal worms, so they typically replace — not supplement — a 3-monthly product like Biheldon or Drontal.

Where Biheldon still fits in a lungworm-endemic household

Even in endemic areas, Biheldon (or any praziquantel + pyrantel embonate product) can fit a worming routine in two specific ways:

1. For other pets in the household — cats, for example, are not at meaningful risk of A. vasorum (feline lungworm is a different parasite, Aelurostrongylus abstrusus, which is rare in UK pet cats). A cat sharing a household with a Milbemax-monthly dog can be wormed quarterly with Biheldon for intestinal cover at a small fraction of the per-tablet cost.
2. In between lungworm courses for breeders and rescues working with very young puppies, where Milbemax dosing has specific weight thresholds. Your vet will guide this.

For most one-dog endemic-area households, though, the right answer is monthly Milbemax (or Advocate) and skip the separate intestinal wormer.

Risk-reduction beyond medication

Prevention is mostly chemical (monthly milbemycin or moxidectin in endemic areas), but you can reduce exposure with simple husbandry:

• Pick up dog faeces promptly — slugs and snails feed on it
• Don’t leave dog toys, water bowls, or chews outside overnight — slugs colonise them
• Check water bowls in the garden before they’re used — slugs sometimes drop in
• Discourage your dog from eating or playing with slugs and snails (easier said than done with some dogs)
• Be especially vigilant after rain, when slug/snail activity peaks

None of these are substitutes for medication in an endemic area — but they reduce the dose of infective larvae your dog encounters.

The bottom line

Lungworm is a serious and increasingly widespread UK parasite that no 3-monthly intestinal wormer covers — not Biheldon, not Drontal, not Panacur. Effective protection requires a monthly prescription macrocyclic-lactone product (Milbemax, Advocate, Nexgard Spectra) in endemic areas. If your dog shows respiratory, bleeding, or unexplained-lethargy symptoms, see a vet — this is one of the parasites where early treatment dramatically improves the outcome.

We sell Biheldon for the intestinal-worm half of UK pet worming — the half it actually covers. For lungworm cover, your vet is the right next step.

See the Biheldon vs Milbemax comparison for a head-to-head on the two products, and the worming frequency pillar guide for how the two products fit together in a year’s worming schedule.

Tags: #dogs#lungworm#angiostrongylus#redirect