Some years ago I interviewed a leading trialler who told me that when he first became involved in the sport he didn?t worry too much about worming his dogs regularly. However, it didn?t take him long to realise that to produce winners he needed to have his dogs in peak condition, so a regular worming programme was started that he has kept to ever since. Dogs are susceptible to a frightening variety of different worms: roundworms, tapeworms, lungworms, whipworms and heartworms. All are unpleasant parasites, but some are more dangerous than others.

Perhaps the most unpleasant is the roundworm, Toxocara canis. Roundworms are white-ish in colour, and get their nutrition from the dog?s food in its intestine. In appearance they look like a piece of cooked spaghetti and can grow up to 9in, though most are smaller. They reproduce rapidly, as they shed eggs continually. The worms have the ability to migrate through the dog?s blood into the lungs, when they are usually coughed up but often re-swallowed. Roundworms are a danger to humans, especially children, and they can migrate to the human victim?s liver, lungs, eyes or even brain. As the scientific name implies, this is a parasite specific to dogs, and the worms don?t reach maturity in the human body.

A particular danger from roundworms is the fact that the eggs can remain dormant for lengthy periods, either inside a host or in the ground. Pregnancy in a bitch can trigger their development, when they migrate to the developing foetus. This is why it?s essential to worm a bitch during pregnancy, and also to worm puppies at regular two-week intervals from three weeks to six months, and then at six-monthly intervals.

An adult dog can usually withstand an infestation of roundworms ? it doesn?t pay a parasite to kill its host ? but puppies are vulnerable, and if untreated the worms can cause the bowel to rupture. Regular worming controls roundworms.

I remember as a child being warned of the dangers of getting tapeworms from undercooked pork, and this may well be one of the reasons why certain religions forbid eating it. Dogs also suffer from tapeworms, but like most parasites, they don?t cause a lot of problems unless there?s a heavy infestation.

Tapeworms are harder to eradicate than roundworms and you can?t treat pregnant or nursing dams, or puppies, for them. They can grow to 2ft.

Tapeworms and fleas

Fleas carry tapeworms, so if your dog eats a flea, it can easily become infected. Ingestion is also the way that tapeworms get into the human system. No-one would knowingly eat a flea, but these creatures are so tiny that accidentally consuming one, perhaps while eating your sandwich on a shoot day, is quite possible. Tapeworms are more dangerous to humans than dogs, as they can cause serious liver damage.

Thirty years ago, Britain was free of lungworm (also known as hookworm), but this nasty parasite is now firmly established here. The blood-sucking lungworm looks like a roundworm, but it has teeth that it uses to attach or hook itself to the dog?s intestine. It changes the attachment site several times a day, leading to blood loss and causing anaemia and iron deficiency. Slugs and snails are the carriers, infecting foxes or dogs that eat them.

The symptoms are breathing problems, nosebleeds and vomiting. This is one worm that isn?t a threat to humans, but it can be deadly to dogs, though most make a full recovery if given the correct medication, which is a monthly spoton special wormer. If your dog doesn?t show any interest in eating slugs or snails this is one that you don?t have to worry about too much.