Feline calicivirus is a common cause of upper respiratory disease in cats, with virulent systemic strains causing severe illness and high mortality even in vaccinated adult cats.
Standard FCV infections cause painful oral ulcers that make eating and grooming difficult for affected cats. The ulcers can be severe enough to prevent adequate food intake, leading to secondary hepatic lipidosis in some cases. Respiratory symptoms cause breathlessness and distress. Virulent systemic strains cause a dramatically worse syndrome - cats develop swelling of the face and legs, pneumonia, jaundice, and often die despite intensive treatment. Outbreaks in shelters and clinics can cause multiple deaths in rapid succession. Cats in shelter environments, where stress and disease exposure are high, bear a disproportionate burden of FCV disease.