***Viruses and bacteria are involved in the complex. The most frequent aetiologic agent is FHV-1, and less frequently feline calicivirus and/or [[Chlamydia and Chlamydophila species|''Chlamydophia psittaci'']] (NB: previously called Chlamydia psittaci var felis) | ***Viruses and bacteria are involved in the complex. The most frequent aetiologic agent is FHV-1, and less frequently feline calicivirus and/or [[Chlamydia and Chlamydophila species|''Chlamydophia psittaci'']] (NB: previously called Chlamydia psittaci var felis) |