# Cat Flu and Viral Infections: Signs and When to Worry Cat flu is the everyday name for the upper respiratory infections caused most often by feline herpesvirus and feline calicivirus. The classic signs of cat flu are sneezing, watery or crusty eyes, nasal discharge, and a cat that suddenly stops eating. Most cats recover with supportive care, but some signs mean you should call a veterinarian the same day. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Sneezing with clear eye or nose discharge is common and often mild, but thick yellow or green discharge, squinting, or a cat that will not eat needs a vet visit. - Feline herpesvirus and feline calicivirus cause most cat respiratory infections, and both can become serious in kittens, seniors, and cats with other illnesses [1]. - A cat that stops eating for more than 24 hours is a concern because cats can develop liver problems when they do not eat. - Fever, trouble breathing, open-mouth breathing, or collapse are emergencies. Go to a vet now. - Keep your cat warm, hydrated, and away from other cats, and do not give human cold or pain medicines, which can be toxic to cats. ## What Cat Flu Looks Like and What Is Normal ### The common signs of cat flu A cat with a respiratory virus usually starts sneezing. The sneezes may come in bursts, and you may see clear droplets on the floor or wall. Within a day or two, the discharge often changes. It can become cloudy, yellow, or green. The eyes may water, and the inner eyelids or the tissue around the eye can look red and swollen. Many cats also get a hoarse meow, a cough, or a runny nose. Some develop small ulcers on the tongue, lips, or gums. Those sores make eating painful, so the cat may walk up to the food bowl, sniff, and walk away. Drooling is another clue, especially if the cat has not drooled before. A mild case can look a lot like a human cold. The cat sneezes, has a slightly runny nose, and still eats and plays. That pattern is common and often improves over several days. ### What is normal and what is not Normal for a healthy cat is no sneezing, clear eyes, a normal appetite, and normal energy. An occasional sneeze from dust or a new litter is normal too. What is not normal is a cat that sneezes constantly, has discharge that changes color, squints or holds an eye closed, breathes with an open mouth, or refuses food for a full day. Those signs point to something that needs a veterinarian. Some cats carry herpesvirus for life. The virus can hide in the body and flare up during stress, such as a move, a new pet, or a boarding stay. A flare often looks like the first illness, with sneezing and eye redness. If your cat has these repeated episodes, tell your vet. ## Main Causes of Cat Respiratory and Viral Signs Several viruses and bacteria can cause the same set of signs. A veterinarian may not be able to tell them apart just by looking, which is why testing matters in some cases. Feline herpesvirus 1 (FHV-1) and feline calicivirus (FCV) are the primary causes of respiratory disease in cats [1]. FHV-1 is a contact-infectious virus that causes acute upper respiratory infections, and it affects cats of all ages, with young cats hit especially hard [2]. A study of cats with fatal respiratory disease found FHV in 12 cats, FCV in seven cats, and both viruses in three cats [1]. Many of those cats also had feline leukemia virus or feline immunodeficiency virus, which can make any infection worse [1]. Other causes include Chlamydia felis, a bacterium linked to conjunctivitis and respiratory disease. In one study of conjunctival swabs, Chlamydiaceae DNA was found in 7.7% of cats, and younger age was a significant risk factor [3]. Ocular signs strongly predicted infection in that group [3]. Feline panleukopenia virus and feline infectious peritonitis virus are different diseases, but they are sometimes tested alongside the respiratory viruses because mixed infections occur [4]. | Cause | Typical clues | How urgent | |---|---|---| | Feline herpesvirus 1 | Sneezing, eye redness, squinting, corneal ulcers, flare-ups with stress [2][5] | See a vet if the eye is held shut, the cat stops eating, or signs last more than a few days | | Feline calicivirus | Sneezing, mouth ulcers, drooling, hoarse meow, sometimes limping | See a vet if the cat drools, has trouble eating, or seems painful | | Chlamydia felis | Often one eye, redness, discharge, younger cats at higher risk [3] | See a vet for eye treatment, since this needs specific medication | | Feline panleukopenia virus | Vomiting, diarrhea, lethargy, not the usual sneezing picture | Emergency. Call your vet right away | | Feline infectious peritonitis virus | Fever, weight loss, belly swelling, breathing changes | Emergency. Call your vet right away | | Feline leukemia or immunodeficiency virus | Long-lasting or repeated illness, poor coat, weight loss [1] | Same-day visit for testing and a care plan | If your cat is coughing instead of sneezing, see [Cat Coughing: When Should You Worry?](/knowledge/veterinary-medicine/parasitic-diseases/cat-coughing-when-to-worry). If sneezing is the main sign, [Cat Sneezing: When to Worry and How to Help](/knowledge/veterinary-medicine/online-vet-and-care-costs/cat-sneezing-when-to-worry) walks through the details. ## Signs of Cat Illness That Mean Emergency Some signs are not wait-and-see. They mean your cat needs care now. - Open-mouth breathing, panting, or breathing that looks like hard work - Blue, gray, or pale gums and tongue - Collapse, weakness, or a cat that cannot stand - A seizure or sudden blindness - A fever with shaking or hiding - Repeated vomiting or diarrhea, especially with blood - A cat that has not eaten or drunk anything for 24 hours - A kitten that is limp, cold, or crying and not nursing Breathing trouble is the most urgent sign. Cats hide illness well, so a cat that is visibly struggling to breathe is already in serious trouble. Do not wait to see if it passes. Eye signs can also be urgent. If your cat holds one eye closed, rubs at it, or the eye looks cloudy, that can mean a corneal ulcer. Herpesvirus is a known cause of eye disease in cats, and a study of domestic cats found a significant link between herpesvirus exposure and oculonasal discharge [5]. An untreated ulcer can damage the eye permanently. ## Safe Things You Can Do at Home While Waiting Home care supports your cat. It does not replace a diagnosis. ### Keep the nose and eyes clean Use a warm, damp cotton ball or soft cloth to gently wipe away crusts from the nose and eyes. Wipe from the inside corner outward. Use a fresh cloth for each eye so you do not spread infection from one eye to the other. ### Help with breathing and eating Run a cool-mist humidifier in the room where your cat rests, or let your cat sit in a steamy bathroom for a few minutes. This can loosen thick mucus. Warm wet food slightly to make it smell stronger, since a stuffed nose dulls the sense of smell. Offer soft food, broth, or plain cooked chicken if your cat will take it. ### Keep your cat comfortable and separate Give your cat a quiet, warm place away from other pets and children. Wash your hands after contact. If you have more than one cat, keep the sick cat in a separate room and use separate food bowls and litter boxes. Some of these viruses spread easily between cats. ### What not to do Never give a cat human cold medicine, acetaminophen, ibuprofen, or aspirin. These can be deadly to cats. Do not use essential oils around cats, and do not force food or water into a cat's mouth, which can cause choking. Do not use leftover antibiotics from another pet. If your cat needs medication, your veterinarian will calculate the dose from your cat's weight and health. Do not guess at a dose on your own. ## What Your Veterinarian Will Check and Test Your vet will start with a full physical exam. They will check the eyes, nose, mouth, throat, and lungs. They will take your cat's temperature and listen to the heart and lungs. They will also ask about appetite, energy, and how long the signs have lasted. Depending on what they find, your vet may recommend: - An eye stain to check for corneal ulcers - Blood work to look at organ function and white blood cell counts - A PCR test to look for viral or bacterial DNA - A chest X-ray if breathing is a concern - Tests for feline leukemia virus and feline immunodeficiency virus, since these can change the treatment plan [1] Newer testing can check for several viruses at once. A quadruplex PCR method was designed to detect feline panleukopenia virus, feline herpesvirus 1, feline calicivirus, and feline infectious peritonitis virus in a single test [4]. Rapid tests for FHV-1 antigen are also being developed, with results in about 10 minutes in one study [2]. Your vet will choose the test that fits your cat's signs. Treatment depends on the cause. Viral infections do not respond to antibiotics, but antibiotics may be used if a bacterial infection is also present. Eye ulcers need specific eye medicine. A cat that will not eat may need fluids, appetite support, or a feeding tube. Your vet will explain the plan for your cat. ## Prevention and Monitoring Vaccination is the main way to lower the risk of severe respiratory disease. Talk with your vet about the vaccine schedule for your cat, especially for kittens and cats that go outdoors or live in groups. Keep stress low. Since herpesvirus can flare during stressful times, a steady routine, plenty of resources, and separate feeding stations in a multi-cat home can help. Keep new cats separated for a period your vet recommends before mixing them. Monitor your cat at home. Watch for these changes: - Sneezing that gets worse instead of better - Discharge that turns thick or colored - A cat that stops grooming - Weight loss or a change in appetite - Any new eye squinting or redness If your cat has a chronic virus, ask your vet what a flare looks like and when to call. Early care often means a shorter, easier recovery. If your cat has other symptoms, such as bad breath, see [Cat Bad Breath: When Is It a Sign of Illness?](/knowledge/veterinary-medicine/vet-visit-decisions/cat-bad-breath-when-to-worry). If a scratch or bite is part of the picture, [Cat Scratch: When to Worry About Infection or Rabies](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-scratch-infection-risk) covers that risk. ## Limitations and When to Contact a Veterinarian This article cannot diagnose your cat. Every cat is different, and the same sign can have more than one cause. Only a veterinarian who examines your cat can give you a diagnosis and treatment plan. Call your veterinarian the same day if your cat: - Has thick yellow or green discharge from the nose or eyes - Squints, holds an eye closed, or has a cloudy eye - Has mouth ulcers, drools, or cries when eating - Has not eaten for 24 hours - Has a fever, is hiding, or seems painful - Has signs that are getting worse after three to four days Go to an emergency clinic now if your cat: - Breathes with an open mouth or struggles to breathe - Has blue or pale gums - Collapses or cannot stand - Has a seizure - Has severe vomiting or diarrhea with blood For a mild case with clear discharge and a normal appetite, a routine visit within a day or two is reasonable. For a kitten, a senior cat, or a cat with another illness, call sooner. Young cats are at higher risk for some of these infections [2][3]. ## Frequently Asked Questions ### Is cat flu the same as a human cold? No, cat flu is caused by viruses that infect cats, mainly feline herpesvirus and feline calicivirus. People cannot catch these cat viruses, and cats cannot catch your cold. The signs can look similar, but the germs are different. ### Can my cat get COVID-19? Yes, cats can be infected with the virus that causes COVID-19, usually after close contact with an infected person. Most infected cats have mild signs or none at all, but some may sneeze, cough, or seem tired. If your cat has breathing trouble or stops eating, call your vet. ### How long does cat flu last? Mild cases often improve over several days to a week or two with supportive care. Some cats take longer, and herpesvirus can flare up again later during stress. If signs last more than a few days or get worse, see your vet. ### Can I catch cat flu from my cat? No, the viruses that cause cat flu do not infect people. You can still spread germs between cats on your hands, clothes, and bowls, so wash your hands and use separate supplies for a sick cat. ### Should I isolate my sick cat from other cats? Yes, keep the sick cat in a separate room with its own food, water, and litter box. These infections spread easily between cats through sneezing, saliva, and shared items. Wash your hands after caring for the sick cat and before handling other cats. ## Related Articles - [Cat Scratch: When to Worry About Infection or Rabies](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-scratch-infection-risk) - [Cat Bad Breath: When Is It a Sign of Illness?](/knowledge/veterinary-medicine/vet-visit-decisions/cat-bad-breath-when-to-worry) - [Cat Coughing: When Should You Worry?](/knowledge/veterinary-medicine/parasitic-diseases/cat-coughing-when-to-worry) - [Cat Sneezing: When to Worry and How to Help](/knowledge/veterinary-medicine/online-vet-and-care-costs/cat-sneezing-when-to-worry) - [Cat Sneezing: Common Causes and When to Worry](/knowledge/veterinary-medicine/online-vet-and-care-costs/cat-sneezing-causes) - [Cat Ear Infection with Redness: Causes and When to Worry](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-ear-infection-with-redness-causes-and-when-to-worry) - [Do Cats Get Colds? Symptoms, Causes, and When to Worry](/knowledge/veterinary-medicine/symptom-guides/do-cats-get-colds) - [How Long Does a Cat Virus or Cat Flu Last? Recovery Timeline](/knowledge/veterinary-medicine/symptom-guides/how-long-cat-virus-last) - [Feline Viral Rhinotracheitis: Signs and Causes in Cats](/knowledge/veterinary-medicine/symptom-guides/feline-viral-rhinotracheitis-signs) - [Cat Respiratory Infections: Etiology, Clinical Signs, Zoonotic Potential, and Management](/knowledge/bacteria/pet-bacteria/cat-respiratory-infections-etiology-clinical-signs-zoonotic-potential-management) - [Feline Upper Respiratory Infections (Feline Herpesvirus, Calicivirus, and Bordetella): Etiology, Clinical Signs, Zoonotic Potential, and Therapeutics](/knowledge/bacteria/pet-bacteria/feline-upper-respiratory-infections-herpesvirus-calicivirus-bordetella) ## References 1. [Feline herpesvirus and calicivirus: Occurrence and pathology in cats with respiratory disease](https://pubmed.ncbi.nlm.nih.gov/41015115/). Topics in companion animal medicine, 2025. 2. [Rapid and sensitive detection of feline herpesvirus-1 using fluorescent microspheres as labels for immunochromatographic test strips](https://pubmed.ncbi.nlm.nih.gov/41779066/). Veterinary research communications, 2026. 3. [Prevalence, risk factors and genetic diversity of Chlamydia felis in cats](https://pubmed.ncbi.nlm.nih.gov/41497455/). Journal of veterinary research, 2025. 4. [The quadruplex TaqMan MGB fluorescent quantitative PCR method for simultaneous detection of feline panleukopenia virus, feline herpesvirus 1, feline calicivirus and feline infectious peritonitis virus](https://pubmed.ncbi.nlm.nih.gov/40521026/). Frontiers in cellular and infection microbiology, 2025. 5. [Tracing feline herpesvirus-1 exposure in domestic cats from Namibia: associations with neutralising antibodies, vaccination, clinical signs, and retroviral status](https://pubmed.ncbi.nlm.nih.gov/42554915/). Veterinary research communications, 2026. ## Further Reading - [Feline Infectious Diseases (Cornell University College of Veterinary Medicine)](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-infectious-diseases) - [Merck Veterinary Manual: Cat Owners](https://www.merckvetmanual.com/cat-owners) - [Cornell Feline Health Center: Health Information](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information)