Cat Infectious Disease Testing: What One Panel Can Catch
· By Dr. Tang
TL;DR — Cats hide illness, so feline infectious disease is found by testing, not by waiting for obvious signs. The framework is 2 tests, 2 questions — antigen for active infection, antibody for immunity — applied across 6 pathogens (panleukopenia, herpes, calicivirus, coronavirus/FIP, FeLV and FIV). 1 rule simplifies the rest: a sick cat gets an antigen test; a vaccine check gets an antibody test.
In Plain Terms
A cat will not tell you it feels unwell — it will hide, groom normally, and purr right up until it can’t. That is why feline infectious disease is found by testing, not by waiting for signs, and why the antigen-vs-antibody distinction matters so much: a positive FeLV antigen means the virus is in the cat right now, while a positive FPV antibody usually just means the cat is protected. Get those two confused and you will isolate a healthy vaccinated cat, or miss a persistently infected one.
This guide is the hub for the six core feline pathogens — panleukopenia, herpes, calicivirus, coronavirus/FIP, FeLV and FIV. Follow the links for the deep dives.
Antigen vs. Antibody: The Foundation
Feline testing uses the same two fundamental approaches as canine testing:
- Antigen tests detect the pathogen directly, indicating active infection.
- Antibody tests detect the immune response, indicating exposure or vaccination.
For feline viruses in particular, this distinction is clinically critical. A positive FeLV antigen test means the virus is present and the cat is likely persistently infected. A positive FPV antibody test usually means the cat is protected. See Antigen vs. Antibody Testing for the full framework.
Feline Panleukopenia Virus (FPV)
The Disease
Panleukopenia — “feline distemper” — is a highly contagious parvovirus that attacks the bone marrow and intestinal lining, causing profound leukopenia, vomiting, and diarrhoea. It is frequently fatal in kittens.
Testing
- FPV antigen test — detects virus in faecal or rectal-swab samples; the standard for acute diagnosis.
- FPV antibody test — assesses immunity from vaccination or exposure.
Interpretation
A positive antigen test in a symptomatic cat confirms panleukopenia and demands immediate isolation. Because the virus is extremely stable in the environment, disinfection and isolation protocols are essential.
Related products: FPV-Ag Antigen Test · FPV-Ab Antibody Test
Feline Herpesvirus (FHV-1)
The Disease
FHV-1 causes feline viral rhinotracheitis — upper-respiratory disease with sneezing, nasal and ocular discharge, and conjunctivitis. After recovery, the virus becomes latent and can reactivate during stress.
Testing
- FHV-1 antigen test — detects active viral shedding.
- FHV-1 antibody test — assesses exposure or immunity.
Interpretation
Antigen testing confirms active infection during clinical episodes. Antibody testing is less commonly used for acute diagnosis but useful for population screening. See Does My Cat Need a Feline Herpes (FHV-1) Test?.
Related products: FHV-Ag Antigen Test · FHV-Ab Antibody Test
Feline Chlamydia (Chlamydia felis)
The Disease
Chlamydia felis is a bacterial pathogen that targets the eyes — the classic presentation is persistent conjunctivitis, often in young cats or multi-cat households, sometimes with mild nasal signs. It is distinct from the viral upper-respiratory pathogens in that the eye, not the airway, is the primary site.
Testing
Antigen or PCR testing on conjunctival swabs confirms active infection. Because conjunctivitis has several causes (FHV-1, calicivirus, Chlamydia, Mycoplasma), testing is what tells them apart rather than treating blindly.
Interpretation
A positive result justifies targeted therapy (and note that Chlamydia felis is a different organism from the human one — the zoonotic risk is minimal). In shelters and catteries, testing guides isolation to stop conjunctivitis sweeping through the population.
Feline Calicivirus (FCV)
The Disease
Calicivirus causes oral ulceration, salivation, and upper-respiratory signs. A highly virulent systemic form can be severe and even fatal.
Testing
- FCV antigen test — detects active infection.
- FCV antibody test — assesses exposure or immunity.
Interpretation
Calicivirus and herpesvirus frequently co-infect and produce overlapping signs, so combined panels are common. See A Feline Triple Test.
Related products: FCV-Ag Antigen Test · FCV-Ab Antibody Test
Feline Coronavirus & FIP (FCoV)
The Disease
Feline coronavirus is common and usually causes mild or no signs. In a small percentage of cats, the virus mutates, causing feline infectious peritonitis (FIP) — a severe, historically fatal systemic disease.
Testing
FCoV antigen testing detects the coronavirus. Interpretation requires care: a positive result indicates coronavirus infection, but not necessarily FIP. FIP diagnosis typically combines clinical signs, antibody titres, and other markers.
Related product: FCoV-Ag Coronavirus Antigen Test
Feline Leukemia Virus (FeLV)
The Disease
FeLV is a retrovirus that suppresses the immune system, predisposing cats to secondary infections, anaemia, and lymphoma. It is a leading infectious cause of death in cats.
Testing
FeLV antigen testing detects the virus itself and is the standard screening test. A positive result indicates infection (though early, transient infection can occasionally clear).
Interpretation
FeLV status has profound implications for management, vaccination, and multi-cat households. Positive cats require lifelong monitoring and separation from negative cats. See What Is the Feline Leukemia (FeLV) and FIV Test?.
Related product: FeLV-Ag Antigen Test
Feline Immunodeficiency Virus (FIV)
The Disease
FIV, also a retrovirus, progressively weakens the immune system over years. Cats may remain asymptomatic for long periods before developing secondary infections.
Testing
FIV antibody testing is the standard screening method, as antibodies persist once a cat is infected.
Interpretation
A positive FIV antibody test indicates infection (or maternal antibodies in very young kittens). FIV-positive cats can live long, good-quality lives with proper management.
Related product: FIV-Ab Antibody Test
The Feline Triple Test: Three Viruses, One Panel
Upper-respiratory disease in cats is usually one of three viruses — FPV, FHV-1 or FCV — and they co-infect so often that a combined panel is the practical default. But the three antibodies are not equal in what they tell you:
| Virus | Positive antigen means | Positive antibody means |
|---|---|---|
| FPV | Active panleukopenia (urgent) | Reliable protection (single serotype) |
| FHV-1 | Active shedding | Exposure — but the virus goes latent for life |
| FCV | Active infection | Exposure — but many strains dodge vaccine |
The key nuance: FPV antibodies predict protection reliably, FCV antibodies do not. FHV-1 goes latent, so a positive antibody says “exposed,” not “immune.” A single panel answers three questions at once, but the three answers mean different things — read them separately.
A Diagnostic Decision Tree
Work through the presenting sign, and the test picks itself:
- Vomiting + diarrhoea, especially a kitten → FPV antigen immediately (mortality ~90–100% untreated).
- Sneezing, ocular/nasal discharge → FHV-1/FCV panel (antigen for active, antibody for immunity).
- Chronic conjunctivitis → Chlamydia/Mycoplasma antigen or PCR.
- Weight loss, fever, anaemia, lymphoma → FeLV antigen + FIV antibody (the retrovirus pair).
- Effusion / neurological signs → FCoV antibody titre + clinical picture for FIP.
The discipline is the same as canine testing: a sick cat gets an antigen test (is it here now?), a healthy cat gets an antibody test (is it protected?). The difference in cats is the added complexity — retroviruses with three outcomes, a coronavirus that only sometimes becomes FIP, and a herpesvirus that never leaves — which is why a quantitative number, not a line, is what separates “exposed” from “sick.”
When Should You Test?
- New kittens or adopted cats — screen for FeLV and FIV before introduction to a household.
- Upper-respiratory signs — test for FHV-1 and FCV.
- Vomiting/diarrhoea, especially in kittens — test for FPV.
- Fever of unknown origin — consider FeLV, FIV, and FCoV.
- Before vaccination — antibody testing can guide protocols.
- Multi-cat facilities — routine screening to protect the population.
Conclusion
Feline infectious diseases are diverse, but rapid, quantitative testing brings clarity. By matching antigen vs. antibody testing to the clinical question and testing early, veterinarians can detect disease sooner, manage infectious cats appropriately, and protect the broader feline population.
Key Takeaways
- Cats hide illness — 2 test types find what observation misses, so testing catches disease early.
- Antigen = active infection, antibody = immunity — the 2-question framework.
- FeLV antigen and FIV antibody are the 2 retrovirus tests — different questions, different meaning.
- Panleukopenia is the 1 urgent one — early antigen testing saves kittens.
- Match the test to the question — 1 sick cat gets antigen; 1 vaccine check gets antibody.
FAQ
What does feline infectious-disease testing cover?
Six pathogens — panleukopenia (FPV), herpes (FHV-1), calicivirus (FCV), coronavirus/FIP, FeLV and FIV — using 2 test types: antigen for active infection and antibody for immunity.
Which test for a sick cat?
One rule for a sick cat: an antigen test, because it detects the pathogen directly and confirms active infection. A positive FeLV antigen is the exception to read carefully — it needs a repeat test 60 days later, because some cats clear the virus.
Which test checks vaccine protection?
One rule for vaccine protection: an antibody test, because it measures the immune response from vaccination or prior exposure. For FPV a low titre (below ~40) is a solid revaccination signal; for FCV it’s a weaker one.
Why are the retrovirus tests different?
The retrovirus tests differ by 2 analytes: FeLV is tested by antigen (virus present now) and FIV by antibody (immune response), so their positive results mean different things.
References
- Greene CE. Infectious Diseases of the Dog and Cat. 4th ed. Elsevier.
- 2020 AAFP Feline Retrovirus Testing and Management Guidelines. PMC11135720.
This content is for educational purposes only. It is not a substitute for veterinary diagnosis — a sick cat should be seen by a veterinarian.