Early in the clinical course of feline pneumonitis, the causative organism may be identified in Giernsa-stained conjunctival smears or scrapings. The elementary bodies are intracytoplasmic. Mycoplasmas occur as extracellular coccoid bodies often seen on the surface of conjunctival epithelial cells. The presumptive diagnosis is based on such typical signs as sneezing, conjunctivitis, rhinitis, lacrimation, salivation, oral ulcers, and dyspnea. FVR tends to affect the conjunctivae and nasal passages, caliciviruses the oral mucosa and lower respiratory tract.
Chlamydial infections result in chronic, low-grade conjunctivitis.
These characteristics may be obscured in mixed infections. Cytologic examination of Giemsa-stained conjunctival scrapings is of value for the identification of chlamydiae and mycoplasmas. A definitive diagnosis is based on isolation and identification of the agent. The oropharyngeal mucosa, external nares, and conjunctival sacs are the preferred sampling sites. Tetracyclines are the most effective against C psittaci.