When asked to help shelters control feline upper respiratory infections, veterinarians face a confusing and discouraging tangle. Feline upper respiratory disease can be caused by any of several agents, including feline herpesvirus type 1 (also known as feline viral rhinotracheitis), feline calicivirus, and Chlamydia psittaci, among others. The three listed all can produce long-term carrier states, in which cats can shed pathogens without showing any clinical signs. Vaccines for all three pathogens protect against severe disease but not against infection or development of the carrier state. In a shelter, new animals of unknown health status are constantly entering the population, and the shelter may lack the funding, facilities, and staff to follow ideal disease control procedures.