feline infectious enteritis (panleucopenia)

This disease is caused by a virus and is fatal, particularly in kittens and young cats if not treated immediately by a vet. The symptoms are listlessness, loss of appetite, vomiting, extraordinary thirst, rise of temperature and rapid deterioration in condition. If a kitten is vomiting and looks poorly, call the vet immediately. Speed is essential. All cats and kittens should be vaccinated.

SOURCE: cats.consultinghealth.com