I am most familiar with hook worms and tapeworms. Hook worms are small and usually not visible to the human eye. Kittens can get hook worms from their mom while nursing or the environment- soil that contains lavara. They can be detected in fecal samples and are treated with an oral medication from your vet. Missy and Bashful were treated for hook worms their first two visits to the vet.
Tapeworms are small white worms that look like little inch worms.
They can be detected visual in the litter box or can appear as dried up rice grains on the kitties backside. Fleas carry tapeworm larva. While grooming cats ingest the infected fleas, and the larva ends up in the cats intestine to grow and reproduce. The nature of tapeworms make them hard to detect in fecal samples. Missy and Bashful had two fecal samples three weeks a part and both can back negative for tapeworms.