Feline calicivirus (FCV) is one of the most common causes of upper respiratory tract disease in cats. This virus, along with feline herpesvirus-1 causes more than 80-90% of all upper respiratory tract infections in cats. FCV is highly contagious, and recovered animals may shed virus for months to years. FCV may be associated with other diseases as well, including arthritis and gingivitis. These investigators have identified a new highly hemorrhagic and fatal form of feline calicivirus from an outbreak in Tennessee. These affected animals suffered vasculitis with involvement of the liver, skin, and lungs. The virus was easily transmitted and rapidly spread to other cats in the facility, with significant mortality even in vaccinated cats. This study proposes to characterize this virus at the genetic level and compare it to other well-known respiratory forms to identify its unique features. This will increase the understanding of disease production by FCV and the reason for the apparent vaccine failures that are becoming more common. The latter information will have an impact on the design of FCV vaccines.