The majority of upper respiratory infections are caused by viruses. Many times U.R.I.s are caused by multipleorganisms. Chlamydia psittici is also a known cause of U.R.I. It is difficult to pinpoint the exact organism causing U.R.I. in a cat,particularly if there is a multiple infection. A second infection causes a different set ofsymptoms.
Many infections are due to a combination of organisms.
Calici can survive in the environment about 8-10 days. FHV-1 survives only18 hours. The principal source of infection is by exposure to another catshedding the virus. The most baffling fact remains. Calici and herpes can be spread by asymptomatic and healthy cats as wellas apparent diseased cats.