Description
Feline herpesvirus-1 (FHV-1), Chlamydia felis, and Mycoplasma felis are key pathogens in feline upper respiratory and ocular disease, often co-infecting. FHV-1 typically causes acute sneezing, serous rapidly becoming mucopurulent nasal and ocular discharge, conjunctivitis, blepharospasm, keratitis (dendritic or geographic corneal ulcers), fever, and inappetence; it establishes lifelong latency with stress-related recrudescence.
Chlamydia felis mainly induces chronic or recurrent conjunctivitis with marked chemosis, hyperaemia, and serous to mucopurulent ocular discharge, often with only mild or absent nasal signs. Mycoplasma felis is associated with conjunctivitis and upper respiratory signs (sneezing, nasal discharge) that can resemble the other two, and all three can coexist, worsening clinical severity.
Diagnosis for all three relies on a combination of clinical pattern and targeted sampling from the conjunctiva and upper airway. Conjunctival and oropharyngeal swabs placed into appropriate transport medium are the primary samples, and corneal/ocular surface cytology may show characteristic inclusions for Chlamydia or mixed bacterial/mononuclear inflammation but is not definitive. qPCR on conjunctival and/or oropharyngeal swabs is the most sensitive method to detect and differentiate FHV1, C. felis, and M. felis: it identifies low organism loads, distinguishes coinfections, and provides cyclethreshold–based estimates of pathogen burden that help interpret whether a detected agent is likely clinically relevant versus incidental carriage.
Repeated or highload qPCR positives in a symptomatic cat strongly support causation, whereas lowload single positives may be incidental and must be interpreted alongside vaccination history, clinical signs, and response to therapy.
