The Classic Comprehensive Handbook of Cat Care: THREADWORMS
The threadworms, Strongyloides stercoralis, is a roundworm parasite of cats, dogs, and humans. Infection with this species and other kinds of threadworms is acquired most commonly when infective larvae penetrate the skin. This can cause red lumps, crusts, and scratching.
And during their migration through the body the larvae can produce signs of respiratory disease, such as a cough. Cats can also become infected by ingestion of infective larvae. Threadworms are very small worms and will not be seen in the stool. When diagnosis is established by a veterinarian, thiabendazole is often used for treatment. Prevent Strongyloides infection by providing your cat with a clean, dry environment since the infective larvae cannot survive without a moist environment.