Is your cat showing signs of illness? Sneezing, a runny nose, or a sudden loss of appetite could be symptoms of cat flu, a common and contagious respiratory infection formally known as Feline Upper Respiratory Infection (URI). This condition, primarily caused by Feline Calicivirus (FCV) or Feline Herpesvirus (FHV), can cause significant discomfort and lead to serious complications if left untreated, especially in kittens and senior cats.