Internal parasites live in your pet’s digestive tract — and, in the case of heartworm, in the heart itself. They cause vomiting, diarrhoea and serious internal damage, and some of them can pass to people. Deworming is compulsory in Spain for dogs, cats and ferrets, at least once a year, and monthly in puppies and kittens. Your vet sets the schedule.
Key facts:
- Where they live: mainly the digestive tract; heartworm lives in the heart and lungs.
- Main types: heartworm (filaria), roundworms and tapeworms.
- Signs: vomiting, diarrhoea, weight loss, a dull coat, a swollen belly in puppies.
- Zoonosis: some worms can pass to people, especially children.
- Compulsory: deworming for dogs, cats and ferrets — at least once a year.
- Puppies and kittens: monthly, on your vet’s schedule.
Internal parasites are invisible, which is precisely the problem: by the time you can see something is wrong, the worm burden is usually well established.
What are internal parasites?
They are worms that live inside the animal, most of them in the digestive tract, where they steal nutrients and damage the gut wall. The most important groups are roundworms and tapeworms in the intestine, and heartworm (filaria), which is transmitted by mosquitoes and lodges in the heart and pulmonary arteries — a far more dangerous proposition.
What signs should I look for?
The commonest are vomiting and diarrhoea, sometimes with visible worms or segments in the faeces. Beyond that: weight loss despite a normal appetite, a dull, poor coat, low energy and, classically in puppies, a pot-bellied appearance despite being thin. Heartworm is different: it shows up as coughing, exercise intolerance and, in advanced cases, heart failure.
Can worms pass to people?
Yes. Several internal parasites are zoonoses: they can infect humans, and children are the most vulnerable, because they play on the ground and are less scrupulous about washing their hands. This is one of the main reasons deworming is a legal duty and not merely good practice.
Is deworming compulsory in Spain?
Yes. Deworming is compulsory for dogs, cats and ferrets, with a minimum of one treatment per year. That is a legal floor, not a clinical recommendation: most pets need it considerably more often.
How often should I deworm my pet?
It depends on age and lifestyle, and your vet will set the schedule. As a general guide, puppies and kittens need deworming monthly in their early months, because they are frequently infected from birth or through the mother’s milk. Adult animals are usually treated several times a year, and more often if they hunt, roam, eat raw food or live with young children. Heartworm prevention is seasonal and depends on where you live, since it follows mosquito activity.
Frequently asked questions
How often must I deworm my dog?
At least once a year by law, but most dogs need it several times a year. Puppies are dewormed monthly. Ask your vet.
Can my dog’s worms infect me?
Some can. They are zoonoses, and children are the most at risk. Good hygiene and regular deworming prevent it.
What are the signs of worms?
Vomiting, diarrhoea, weight loss, a dull coat and, in puppies, a swollen belly.
What is heartworm?
A parasite spread by mosquitoes that lodges in the heart and lungs. It causes coughing and exercise intolerance, and it is far more serious than intestinal worms.
A parasite left unchecked means tests, treatment and, in the case of heartworm, a long and costly course. Petplan España (Petplan Ibérica, S.L.) reimburses 100% of the vet bill up to €3,100 a year, with a €45 excess, at any vet you choose. See the policy terms.
