Internal deworming is one of the most important — and at the same time most overlooked — preventive care measures for dogs and cats. Unlike fleas or ticks, internal parasites are not visible to the naked eye, but they can seriously affect your pet's health and, in some cases, be passed on to people.
What internal deworming is
Internal deworming consists of administering antiparasitic products that eliminate the organisms living inside the animal's body, mainly in the digestive tract, although some affect other organs such as the heart or lungs. It is both a preventive and a treatment measure that helps keep your companion healthy and reduces the spread of parasites within the home environment.
Difference from external deworming
It is important not to confuse the two concepts. External deworming targets parasites that live on the skin and coat, such as fleas, ticks or certain mites. Internal deworming, on the other hand, fights those that lodge inside the body. They are complementary treatments: one does not replace the other and, in fact, some external parasites can transmit internal parasites, so both plans must be coordinated. If you want to learn more about the former, you can read our guide on external parasites: symptoms and prevention.
Most common types of internal parasites
There are many internal parasites that can affect dogs and cats. These are the most common groups in our area:
- Roundworms (intestinal worms): very common round worms, especially in puppies, which can be transmitted even before birth or through the mother's milk.
- Tapeworms: flat worms that usually reach the animal when it ingests fleas or infested prey; sometimes segments resembling grains of rice are seen near the anus.
- Heartworm (dirofilariasis): transmitted by mosquito bites and affecting the heart and lungs; it is a serious disease that requires specific prevention.
- Giardia: a microscopic protozoan that causes persistent diarrhoea and can be difficult to eliminate completely.
Symptoms of internal parasites
Many infested animals show no obvious signs at first, which makes prevention even more important. When they do appear, the most common symptoms are:
- Diarrhoea or soft stools, sometimes with blood or mucus
- Vomiting, occasionally with worms present
- Weight loss despite eating normally
- Swollen abdomen, typical in puppies
- Dull coat, weakness or slow growth
- Coughing or breathing difficulties in cases that affect the heart and lungs
If your pet repeatedly experiences vomiting or loss of appetite, it is worth having it assessed by your vet; in the case of cats, our article on what to do when your cat won't eat and is vomiting may help.
Zoonosis risk: parasites that affect people
Some internal parasites of dogs and cats are zoonotic, meaning they can be transmitted to people. Infection usually occurs by unknowingly ingesting microscopic eggs present on surfaces, soil or contaminated sand. Young children are especially vulnerable, as they tend to put their hands in their mouths and play on the ground or in sandy areas.
That is why internal deworming not only protects your pet: it is also a public and family health measure. Simple habits help too, such as washing your hands after playing with the animal, picking up its faeces and keeping play areas clean.
“Deworming isn't only for your pet: many parasites also affect people. A proper schedule protects us all.”
General deworming schedule
The ideal frequency depends on the animal's age, its lifestyle, access to the outdoors, contact with other animals and the geographical area. The following table is a general reference; the specific plan, products and doses should always be indicated by your vet.
| Life stage | General frequency |
|---|---|
| Puppies and kittens | From the first weeks and frequently during the first months |
| Healthy adults | Several times a year, depending on lifestyle and risk |
| Pregnant and nursing females | Before mating, during pregnancy and after birth, always under veterinary supervision |
| Animals with outdoor access or that hunt | Higher frequency due to their greater exposure |
Why it is so important in puppies
Puppies and kittens deserve a special mention. Many are born already infested or become infested through their mother's milk, so they can carry a significant parasite load from very early on. In such young animals, worms can cause stunted growth, anaemia and serious digestive problems. That is why internal deworming in puppies begins very early and is repeated frequently during their first months, alongside their vaccination plan.
In fact, prevention and vaccination go hand in hand at this stage. You can consult our guides on which vaccines your dog needs and on cat vaccines for a complete overview of the preventive schedule. And if questions arise about their general health, our internal veterinary medicine team can help you with personalised follow-up.
Assess each case with your vet; the right treatment depends on each animal's age, weight, health status and history.
Frequently asked questions
How often do I have to deworm my pet internally?
There is no single answer, because it depends on each animal's age, lifestyle and risk. That is why it is best to discuss the plan with your vet, who will design a schedule tailored to your dog or cat.
If my cat doesn't go outside, does it still need internal deworming?
Yes. Although the risk is lower, parasites can enter the home through footwear, other animals or the food itself. An indoor cat also needs prevention, although the frequency may differ from that of an animal with outdoor access.
Does internal deworming replace external deworming?
No. They are different and complementary treatments. Internal deworming fights parasites inside the body, and external deworming those on the skin and coat. For complete protection it is necessary to keep both plans coordinated.
Ask about your preventive plan at Clínica Veterinaria Somo
Internal deworming is one of the best investments you can make in your pet's health and in your whole family's peace of mind. At Clínica Veterinaria Somo, in Somo (Cantabria), we help you set the most suitable schedule based on your companion's age and lifestyle. Book an appointment through our contact page or call us on 942 51 00 66 and we will design their preventive plan together.
