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Roundworm in Dogs: UK Guide to Prevention and Treatment

Roundworm (Toxocara canis) is one of the most prevalent internal parasites in dogs in the UK, with studies suggesting that a significant proportion of dogs carry some level of worm burden at any given time. Beyond affecting your dog's health, Toxocara eggs in soil can potentially cause serious illness in humans — making regular worming a genuine public health responsibility as well as a welfare one.

About Toxocara canis

Toxocara canis is a large nematode (roundworm) that lives in the small intestine of dogs. Adult worms can reach 18cm in length and produce thousands of eggs per day that pass out in the dog's faeces. These eggs are not immediately infectious — they require two to four weeks in the environment to develop into the infectious larval stage (L2), making the environment (particularly soil and sandpits) the main source of transmission to both dogs and humans.

Transmission routes in dogs include ingestion of larval eggs from the environment, consumption of infected earthworms, birds or rodents (paratenic hosts), and transplacental and transmammary transmission from infected mothers to puppies. This last route is the most important: virtually all puppies born to infected mothers are born with roundworms or acquire them through the milk, making early worming of puppies essential. Adult dogs with mature immune systems typically develop resistance to patent (egg-producing) infections, though larval migration continues in tissue.

Signs of Roundworm Infection

Adult dogs with roundworm infections often show no clinical signs, particularly with light burdens. Heavy infections — most commonly seen in puppies — cause a pot-bellied appearance, poor coat condition, diarrhoea (sometimes with worms visible as spaghetti-like strands in the faeces or vomit), reduced growth and general unthriftiness. In severe cases in young puppies, roundworm masses can cause intestinal obstruction, which is a medical emergency.

Migrating larvae can cause respiratory signs ('milk larva') in puppies — coughing and nasal discharge — as the larvae pass through the lungs during their migration. Most adult dogs in good health carry very low burdens and show no symptoms, but regular preventive treatment remains important to reduce environmental egg contamination and protect human health, particularly in households with children who may play in soil or sandpits.

Human Health Risk

Toxocara eggs in the environment can infect humans if accidentally ingested — most commonly children who play in contaminated soil or sandpits. In humans, the larvae migrate through body tissues (visceral larva migrans), potentially causing fever, cough, liver enlargement and, in the most serious cases, vision loss (ocular larva migrans) if larvae reach the eye. Public Health England estimates there are around 50 new cases of ocular toxocariasis in the UK each year, predominantly in children.

The practical preventive steps are simple: regular worming of dogs, prompt and responsible disposal of dog faeces (bagging and binning) and handwashing after contact with soil or dogs. The RSPCA, PDSA and BVA all emphasise regular worming as a core component of responsible dog ownership. Keeping worming up to date is not just about your dog's health — it protects children and the wider community.

Treatment and Prevention

Puppies should be wormed every two weeks from two weeks of age until three months old, then monthly until six months old. Nursing mothers should be wormed at the same time as their puppies. After six months, adult dogs should be wormed every one to three months depending on lifestyle and risk — dogs that hunt, scavenge or have regular contact with children should be wormed more frequently.

Effective roundworm treatments available from your vet include fenbendazole (Panacur — a safe and gentle product suitable for puppies, pregnant and nursing females), pyrantel, milbemycin oxime, and combination products that also cover tapeworm, lungworm and other parasites. Panacur granules or liquid from a vet or online pharmacy cost approximately £5–£10 per treatment for an average-sized dog. Prescription combination products covering roundworm, tapeworm and lungworm together (such as Milpro, Drontal or Endogard) cost £8–£20 per treatment. Using your vet's written prescription to source these online can significantly reduce the cost.

Find a Vet Near You

Discuss your dog's individual worming programme with your vet — it depends on lifestyle, risk and which parasites are relevant in your area. Use CompareMyVet at app.comparemyvet.uk to compare local vet prices and find a practice near you.