What is the difference between FCV and FHV-1?

Feline calicivirus (FCV) and feline herpesvirus-1 (FHV-1) are the two main viral causes of feline upper respiratory disease. FCV classically causes oral ulcers and can have limping or virulent systemic forms, while FHV-1 causes sneezing, conjunctivitis, and corneal ulcers with lifelong latency.

Antigen or antibody — which test should I use?

Use antigen testing on swabs when a cat has active respiratory signs, to identify the current pathogen. Use antibody testing in serum/plasma to assess vaccination status or past exposure. Quantitative tests can combine both to give a complete picture.

Why distinguish FCV from FHV-1?

Although the clinical signs overlap, management differs — FHV-1 patients may benefit from antiviral therapy, while FCV is managed supportively with strict hygiene due to its environmental hardiness. Accurate identification guides treatment and infection control.

Feline Calicivirus and Herpesvirus Testing: A Complete Guide

Feline calicivirus (FCV) and feline herpesvirus-1 (FHV-1) are the two most common causes of upper-respiratory disease in cats. Together, they account for the vast majority of “cat flu” cases. Because their signs overlap heavily, accurate testing is essential to identify the culprit and guide treatment. This guide covers testing for both viruses.

The Two Viruses at a Glance

Feline Herpesvirus-1 (FHV-1)

Causes: feline viral rhinotracheitis (FVR).
Signs: sneezing, nasal discharge, conjunctivitis, ocular discharge, fever.
Key trait: becomes latent after infection and reactivates during stress — a lifelong infection.

Feline Calicivirus (FCV)

Causes: oral ulceration, salivation, upper-respiratory signs.
Signs: mouth ulcers, drooling, sneezing, nasal discharge, limping (in some strains).
Key trait: a severe systemic form can be highly fatal.

The two frequently co-infect, producing a combined clinical picture.

Antigen vs. Antibody Testing

Antigen Testing (Active Infection)

Detects the virus directly in ocular, nasal, or oral swabs.

Best for: confirming active infection during a clinical episode.
Answers: “Is the virus present right now?”

Antibody Testing (Exposure/Immunity)

Detects the cat’s immune response.

Best for: population screening and immunity assessment.
Answers: “Has the cat been exposed or vaccinated?”

Related products:

The Feline Triple Test

Because FHV-1, FCV, and panleukopenia virus (FPV) all cause upper-respiratory or systemic signs, a triple test that screens for all three in one step is highly convenient. It allows a clinician to rule in or out the three most common feline viral pathogens from a single sample.

For more, see A Feline Triple Test: One Simple Step to Check for Three Common Viruses.

When Should You Test?

Upper-respiratory signs (sneezing, discharge, conjunctivitis) — test for FHV-1 and FCV.
Oral ulcers or drooling — suspect FCV.
New cats entering a multi-cat household or shelter — screen before introduction.
Recurrent respiratory episodes — FHV-1 reactivation.

Interpreting Results

Positive Antigen Test

Confirms active infection. Note that FHV-1 can reactivate and shed intermittently, so a positive result reflects current shedding.

Positive Antibody Test

Indicates exposure or vaccination. Because FHV-1 is lifelong, most adult cats have antibodies — this does not indicate current disease.

Negative Results

A negative antigen test during a clinical episode may mean the signs are caused by the other virus (or a non-viral cause). Testing both viruses — or using the triple test — improves diagnostic yield.

Treatment and Management Implications

FHV-1 — antivirals (e.g., famciclovir), supportive care, and stress reduction (to prevent reactivation).
FCV — supportive care; the systemic form requires intensive treatment.
Both — isolation of affected cats and good hygiene to prevent spread.

In the Bigger Picture

FCV and FHV-1 are two of the six major feline infectious diseases. For the complete landscape, see Feline Infectious Disease Testing: The Complete Guide.

Conclusion

Feline calicivirus and herpesvirus are the workhorses of “cat flu.” Rapid, targeted testing — whether individual antigen/antibody tests or the convenient triple test — helps clinicians identify the cause, treat appropriately, and protect the feline population.