Worms
The most occurring internal parasite with cats is without a doubt worms. The round-worm and tapeworm which both belong to the “roundworms” occur the most (Human beings and especially children can get infected with these parasites which is usually caused by touching the droppings (sandbox), but also by swallowing through the mouth via the animal itself (eggs which are stuck to the fur).
Round-worms
There are a number of causes due to which your cat can get infected with round-worms. The infection of round-worms often already takes place in the uterus or straight after birth through the mother’s milk. “Interim hosts” can also infect your cat. Interim hosts can be: fleas, preys (birds, mice) but also droppings of another animals (eggs of a worm can for example survive in the ground very long) can infect the cat. As you might have noticed there is a huge chance that your cat gets infected with such a parasite and the only remedy is to worm your cat regularly(adult animals, about 4 times a year). Pay attention to it that you use a means which both fights round-worms and tapeworms.
Tapeworms
The infection of a tapeworm only takes place by means of an interim host like birds, mice, fleas and droppings. The tapeworm has a long flat shape and consists of a head, neck and a body which consists of links. By loosing some links now and then the tapeworm keeps infecting his host and eggs accompany the faeces which results in an infection source. The infection risk is large and the only solution is to worm regularly. In case of infection with worms in an early stage you barely observe symptoms and it is therefore wise to immediately worm a (new) cat if it isn’t clear when this happened for the last time.