Like vomiting, diarrhea is a symptom of an underlying condition and is not an illness in itself.

Symptoms
Pungent, liquid-like faeces; these may be passed frequently, necessitating many trips to the litter tray, or appear as ‘accidents’ around the home. If your cat is suffering from colitis an inflammation of the colon, his faeces will contain quite a lot of mucus and bright red blood. Another symptom of colitis is tenesmus, where the cat strains to defecate; this latter symptom is often mistaken for a symptom of constipation. Diarrhea often leads to dehydration, so your cat may appear slightly disorientated.

Causes
Diarrhea may simply be a symptom of overeating or stress. Intestinal worms are a common cause of diarrhoea, as are foreign bodies in the digestive system and fungal infections.

What to do
Prevent the cat from eating anything, but ensure that he is given adequate amounts of drinking water. If the diarrhoea is acute, provide the cat with a rehydrating fluid and contact the vet. Keep your cat where you can see him, covering the floor with newspapers, or something similar, to keep your home clean. Note the times of his motions, and also the consistency, colour and quantity of the diarrhea. By doing this, you will help the vet to find the cause of the sudden diarrhea, and to treat the problem effectively.

Treatment
The treatment for diarrhea depends upon the underlying cause. If it is due to internal parasites, then anthelmintics wormers will be used to rid the cat of the infestation, while antibiotics will be used for infections. Diarrhoea can cause the cat to dehydrate, and can lead to irreparable body damage particularly of the kidneys and even death. In all cases of severe diarrhea where overeating is not the cause, if it persists, or if there is blood in the motions, consult your vet immediately so the cat can be treated at once.