Worms die when their host dies

How long does a wormer actually work?

Duration of the worming treatment

If you give your dog or cat a wormer, it will last for around 24–72 hours. During this time, the worms and their stages of development, which are located in the animal's intestines, are killed. This means that after around 24–72 hours, the dog or cat no longer has any worms in them and no longer excretes any contagious worm eggs.

How long does a wormer cure protect against re-infection?

Your dog or cat can then be re-infected immediately after the treatment by picking up new worm eggs from the environment. If they do this, it takes a few weeks to months, depending on the type of worm, until new worms have developed from these eggs or the worm larvae contained in them in the animal's intestine and lay eggs, which can be excreted again. The duration of the development process is different for different types of worms:

  • In the case of roundworms, this takes around four to five weeks,
  • usually longer with tapeworms.
  • For hookworms, which are rarely found, it can also be less than four weeks.

Whipworms even need at least two and a half months to develop in the host.

This means that worming lasts around 24–72 hours and the animal can become infected again the day after the worming. However, adult worms and infectious eggs are only found again in the intestines or feces of the animal after a few weeks.

The time at which an infectious worm is picked up and the development time of the worms determine when worms are again present in the cat's intestine after worming and when infectious eggs are excreted.

Why is worming important in dogs and cats?

It's not necessarily about your dog or cat always being completely worm-free. The main aim is to stop a worm infestation before it becomes too strong and harms the animal, and to keep the excretion of infectious eggs low. If the risk of infection is normal, four deworming operations per year are recommended every three months. You can find out an individual deworming recommendation for your animal here: