Firstly, congratulations on rescuing this kitten and giving her a loving home. There are three main reasons for foul smelling feces in young kittens. Firstly, the food a cat is fed can be responsible for foul-smelling feces, and while some foods are more likely to have this result than others, this also depends on your individual cat’s metabolism and history. However, food alone is unlikely to result in such a pungent smell. Parasitic worms are another common cause of bad smells and you were right to have this checked. The third possibility, and the one that most often results in the worst odors of all 3 causes, is the microscopic, spore-forming, single-celled parasite called coccidia. Coccidian parasites are relatively common residents of the intestinal tracts of animals, and actual infection of host animals often only occurs in young animals and after stress. This is why kittens can sometimes arrive at a new home seemingly perfectly healthy, only to develop diarrhea some days later.

While you have not mentioned whether your kitten is also suffering from diarrhea, I will assume that this is either the case, or that her stools are at least loose. Diarrhea is the primary sign of coccidiosis, and blood and mucous can follow in untreated cases. In advanced cases, animals can become lethargic, dehydrated and lose their appetite. For this reason, your kitten needs to receive a course of drugs such as sulfadimethoxine from your vet. Any drug your vet prescribes will not kill the organism but merely prevent it from reproducing – meaning that it might take some time for your kitten to return completely to normal (normally once she has developed a good level of natural immunity herself).