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This page is in serious need of updating, which I hope to complete during 2017.


What is Cat Flu?

Feline Herpes

(Feline Viral Rhinotracheitis)

Feline Calici Virus

Virulent New Strain of Calici Virus


How is It Caught? The Stress Factor Prevention Symptoms Diagnosis Support



Antibiotics Steaming Nasal Drops Mouth Ulcers
L-Lysine Interferon Corneal Ulcers Flushing Tear Ducts


Our Experiences with Cat Flu
Harpsie George and Indie



What is Cat Flu?

There are two main upper respiratory viruses common in cats, which are often referred to as "cat flu" in the UK:


  • feline herpes or FHV-1 (also known as feline viral rhinotracheitis or FVR); and

  • feline calici virus (FCV).

Cats who receive the standard FVRCP vaccinations as a kitten are vaccinated against these diseases: the FVR part of the vaccination package stands for feline viral rhinotracheitis, and the C part stands for calici virus (the P stands for panleukopenia virus). However, there are a number of different strains of these viruses, so (similarly to the human flu jab) vaccination cannot confer 100% protection.


Harpsie has feline herpes, but I'm also going to cover feline calici virus on this page.


The Winn Feline Foundation has a good overview of feline herpes.

The Winn Feline Foundation has a good overview of calici virus.

Mar Vista Vet has helpful information about  upper respiratory disease in cats.

The Feline Advisory Bureau has a good overview of upper respiratory disease in cats.

College Station Cat Clinic has a good summary of cat flu.


Virulent New Strain of Calici Virus

A new, extremely severe strain of calici virus has been seen in the USA, which is fatal in up to 50% of the cats who contract it. These cats may exhibit swelling of the head and paws, and bleeding from the nose or back passage. Fortunately, this is still a relatively rare strain.


DVM Vac discusses the new, severe strain of calici virus. 

Best Friends Animal Society reported in April 2007 that a vaccine has now been developed for this virulent strain.

Cat Channel has a report from Dr Gary Norsworthy on the symptoms of the new strain of calici virus and the new vaccine.


Catching Cat Flu

In order to catch cat flu, a cat must come in contact with the virus, either via a sick cat or via a carrier cat. Many cats who catch cat flu become carriers - this means they may shed the virus occasionally (often when they are stressed) in their saliva and nasal secretions. The shedding cat may seem to have a mild attack of cat flu at such times, though some cats do not appear ill at all whilst shedding.


Both feline herpes and calici virus infect a cat via the eyes, nose or mouth. Cat flu may be spread directly or indirectly, i.e. via shared litter boxes, food dishes, or even carried in by human members of the family on their hands or clothing.


The Stress Factor

It is thought that there is a stress component to flare ups of the FVR virus. Although the frequency of attacks has decreased as Harpsie has got older, it is true that he still sometimes gets his FVR snuffles when he is under stress, and during these times he is shedding the virus. When Tanya died, Harpsie went down with cat flu within a week. Within ten days of our move to the USA, which Harpsie seemed to cope with very well at the time, Harpsie had his first FVR flare-up in a number of years, which coincided with a bad fall which affected his arthritic leg.



The description "cat flu" can be misleading, because it makes it sound like a minor illness, whereas cat flu can be serious, particularly in kittens, in elderly cats or in those with weakened immune systems.


Although Harpsie had the usual FVRCP vaccinations as a kitten, he unfortunately developed FVR before he was 4 weeks old, before he had his vaccinations. It was touch and go, and may partly explain why Harpsie has always been rather delicate. Our George, an older rescue who went down with cat flu, was also extremely ill.


The main way to prevent cat flu is via the standard feline vaccinations. These often prevent a cat catching cat flu, or at least ensure that the cat only has a mild bout. Recently there is controversy over the need for regular vaccinations of cats, but, having gone through cat flu in our home, I would always opt to vaccinate my cats against cat flu. In the USA and Canada, the guidelines are now for the standard vaccinations (which cover cat flu) to be given every three years; however, the recommendation for Europe and Australia, where the types of vaccine used tend to be different to those in the USA, is still to give annual vaccinations.


One other way to prevent cat flu is always, always to quarantine any new cats entering your home. Often cat flu will not flare up for a few days after a cat arrives, so ideally you want to quarantine a new cat for a good two weeks. This is important because there appears to be a stress element to cat flu, so a sufferer arriving in a new home may appear healthy initially, but then go down with cat flu a few days later (as happened to our George). This also ensures that introductions are slow, which increases the chance of them being successful.


Feline Advisory Bureau mentions how the calici virus vaccination occasionally causes limping kitten syndrome in kittens.



The usual symptoms are very similar to those we experience when we have a cold - sore, runny eyes, sneezing, a runny nose or nasal congestion, loss of appetite (often caused by an inability to smell the food because of nasal congestion) and fever.


In addition, in severe cases of feline herpes, conjunctivitis may develop, or ulcers may be seen on the eyes (corneal ulcers).


Cats with the calici virus often have mouth ulcers, which may cause them to drool, and in some cases they may limp ("limping kitten syndrome" is sometimes seen in kittens after they have received their feline calici virus vaccinations). In severe cases of calici virus, pneumonia may result.


Pet Education has a helpful table showing the different symptoms that are seen, depending upon whether your cat has FVR or calici virus.

Feline Advisory Bureau describes the limping syndrome sometimes seen in cats with the calici virus.



Some vets may send a swab from the cat to be tested for the cat flu viruses. The most accurate test for feline herpes is the PCR (polymerase chain reaction) test, which is now available from a number of laboratories. However, my vet has always diagnosed my cats by symptoms alone.



Feline Herpes List is a support group for people whose cats have herpes and other upper respiratory diseases.



Since cat flu is viral, it cannot be cured; rather, the cat's body must fight off the infection, which takes around 3-14 days. However, there are a number of supportive treatments which may help the cat fight the infection and which can certainly make the cat feel more comfortable.


Cats with cat flu often lose their sense of smell, which can make them not want to eat. It is essential for cats to eat, however, in order to keep their strength up and avoid the risk of developing a potentially lifethreatening condition called hepatic lipidosis. Tanya's Feline Chronic Renal Failure Information Centre has tips on getting cats to eat.



Although herpes and calici are viruses, and as such will not respond to antibiotic treatment, many vets do routinely prescribe antibiotics, particularly for vulnerable cats, because opportunistic secondary bacterial infections are very common in cats with cat flu.



Steaming your cat can help clear the nasal passages and make the cat feel more comfortable. Harpsie has been having steams for years because he suffers from chronic post-viral rhinitis ("the snuffles"), and he loves them. He likes them in the lounge, then he can stay in his basket afterwards but still have some company. This is how we steam Harpsie:

  • put cat in a secure carrying basket and lock it.

  • place a bowl of boiling water in front of the basket (where the cat can't dip his/her paws in, naturally).

  • drape the whole lot with towels and leave for 15-20 mins (check regularly to ensure cat is not distressed).

  • Do this three times a day while symptoms are present.

Nasal Drops

Saline nose drops may help if your cat is very congested. Your vet will tell you which ones are safe to use and how much to give. One American brand is Little Noses (1/8% phenylephrine), which is a decongestant nose drop for children.  A commonly prescribed dosage for cats is one drop in each nostril twice a day. However, this brand now apparently has preservatives added, which would make it unsuitable for cats. You need drops containing only buffered sterile saline solution, and these should only be used for a maximum of three days, or they may cause a rebound effect.


The Feline Advisory Bureau discusses chronic nasal discharge in cats, which may be a result of infection with cat flu.


Mouth Ulcer Treatments

Cats with the calici virus often develop mouth ulcers. If you want to try holistic methods, Slippery Elm Bark can be made into a syrup and used to help heal mouth ulcers - this has been found to be a very effective treatment. See Constipation for more information about Slippery Elm Bark and how to make the syrup.


Another natural remedy for mouth ulcers is to mix white cheddar cheese with water to make a paste and spread it on the gums. The enzymes in the white cheddar cheese are supposed to eat the bacteria and help alleviate the infection, though I have not tried this myself and would not recommend it for dental problems other than mouth ulcers (see  Dental Problems for more information on dealing with dental problems generally).


I did try Eel Serum homeopathic remedy for Tanya, and I would say it did help, though perhaps not as much as the SEB might have done.


For severe mouth ulcers, antibiotics may be necessary; while for really obstinate ulcers, particularly in End Stage Renal Disease, you may need to consider using a treatment called sucralfate, which forms a protective coating over the ulcers and allows them to heal. Trade names for this drug include Antepsin in the UK, Carafate in the USA and Ulcogant in Germany.


Mar Vista Vet has information about sucralfate.



Lysine and arginine are both amino acids. The herpes virus requires arginine to replicate. Lysine is an arginine antagonist, which means it blocks the virus accessing arginine and thus reduces the ability of the virus to replicate.


The usual recommended dose for a cat suffering from feline herpes is 250mg twice a day, and a maintenance dose for chronic sufferers is usually 250mg once a day, but be guided by your vet. L-lysine is widely available at health food stores (usually in the amino acid section), in pill, capsule or paste (called Ensyl) form. Be sure you buy a brand which does not contain propylene glycol, because this can cause anaemia in cats. You can either give the l-lysine separately or mix it with your cat's food.


California Veterinary Supply sells L-lysine in powder form for US$10.39 for 100g (just under 4 ounces) or 600g for US$41.99. They also sell the gel form.

Medi-vet in the USA sells L-lysine in a variety of forms.

Vitamin Shoppe sells a number of brands of L-lysine.

Duralactin Feline L-lysine is a combination of L-lysine, microlactin and essential fatty acids. It is supposed to have a taste that is appealing to cats.  I think other products would be cheaper and would contain more L-lysine.

Effect of oral administration of L-lysine on conjunctivitis caused by feline herpesvirus in cats (2002) Stiles J, Townsend WM, Rogers QR & Krohne SG American Journal of Veterinary Research 63(1) pp99-103 concluded that "oral administration of lysine may be helpful in early treatment for FHV-1 infection by lessening the severity of disease".

Efficacy of oral supplementaton with L-lysine in cats latently infected with feline herpesvirus (2003) Maggs DJ, Nasisse MP & Kass PH American Journal of Veterinary Research 64(1) pp37-42 found that a dose of 400mg a day of L-lysine reduces shedding of the virus after a stressful incident (rehousing).

Effects of dietary lysine supplementation in cats with enzootic upper respiratory disease (2007) Maggs DJ, Sykes JE, Clarke HE, Yoo SH, Kass PH, Lappin MR, Rogers QR, Waldron MK, Fascetti AJ Journal of Feline Medicine and Surgery 9(2) pp 97-208 investigated feeding a diet with additional lysine to cats. This would be helpful as a way of controlling herpes in feral colonies. Unfortunately a definitive conclusion regarding giving L-lysine in this way was not reached, but studies are continuing. 



Interferon is produced naturally in the body in response to a viral attack. An artifical form of interferon has been developed. This is a type of anti-viral drug which stops infected cells from reproducing. In Europe it is available in feline form, but this is not yet available in the USA, where the human form of interferon is used off-label in cats.


Interferon is often used to treat FIV, but I am not aware of any scientific studies to date on its effects on feline herpes, in fact I am surprised how little information there seems to be available about using it for this purpose. However, it is sometimes given to cats with herpes, particularly to those with corneal ulcers, and appears to be a safe treatment with very few side effects.


The University of Glasgow explains more about how natural interferon works on viruses (pages 9-11).

Diseases and immunity of the ocular surface (2001) Munger R, Presentation to the World Small Animal Veterinary Association World Congress mentions that interferon may be effective when used for acute herpes infections.

Tally's Page has information about the use of interferon in cats.


Treatments for Chronic Eye Problems, including Corneal Ulcers

Cats who catch FVR may have chronic eye problems, including conjunctivitis, discharge and corneal ulcers. Indie and Harpsie both have ongoing eye discharge problems, for which Indie has been treated with both steroid eye drops and antibiotics. Whenever she's on treatments, her eyes clear up, but within a week of stopping any treatment, her eyes are back to their normal runny selves. Fortunately we have not had to deal with corneal ulcers.


Zigler Veterinary Professional Corporation has information on treating chronic eye problem, including corneal ulcers, from a veterinary opthalmologist.

Corneal diseases of dogs and cats (2002) Sapienze JS is a presentation to the 27th World Small Animal Veterinary Association Congress.

Veterinary Partner discusses conjunctivitis caused by herpes virus, and includes photographs.

Animal Eye Specialists discuss the effects of herpes on the eye, and includes photos of affected eyes.

Animal Eye Specialists have information about corneal ulcers.

Vet Info has information on eye drops and other medications used for herpes-affected eyes.

Pet Place discusses epiphora, runny eyes which often cause rust-coloured stains on the cat's face.


Flushing Tear Ducts

Indie has constant runny eyes as a result of her herpes infection. It is possible to flush through the tear ducts to see if this helps, but this requires general anaesthesia, so I have not opted to have it done separately. We did agree to it being done when Indie needed emergency surgery for an abscess once, but unfortunately none of the instruments available were small enough for her tiny tear ducts.







Our Experiences with Cat Flu



Harpsie has always had a kind of rusty eye discharge, as you can see in the photo of him as a kitten on the right. This is sometimes seen anyway in Persian cats with the orange (red) gene, which Harpsie (being a cream shaded cameo) has; but in his case it is also because he is a cat flu sufferer - he caught cat flu when he was not yet four weeks old, and nearly died from it. Harpsie also tends to be a bit snuffly and to snore, which is partly because of his cat flu, but also because he is a Persian with asthma.


The first time that this discharge really flared up was rather embarrassing. I came in from work to find drops of dried blood on the wallpaper and skirting board close to where Harpsie used to lie. Petrified, I rushed him to the vet immediately, only to discover it was from a flare up of this eye discharge! 


Harpsie snuffled his way through his early years. He needed regular steaming sessions and courses of antibiotics when his cat flu flared up, which it did two or three times a year. His eyes dripped so much that I crocheted a blanket for him to lie on that would protect our furnishings. However, he would go through periods when his face was clean and clear, and during these periods he did not snuffle much, if at all.


As Harpsie grew older, these interludes increased, and in fact he had his last flare up of cat flu in April 2004, more than two years before he died. I am glad he did not have to deal with the snuffles once he was a teenager.


Other Family Sufferers: George and Indie

Harpsie is not the only cat in our family with cat flu. George and Indie are both sufferers; but they did not catch it from Harpsie. 


George was an elderly stray who came to live with us in the summer of 1999. George had been taken to my vet as a stray. My vet found that George had a hyperactive thyroid, so she operated for free and then placed him with me. Since George's vaccination history was unknown, my vet had started him on a course of FVRCP vaccinations but because of his surgery, George had not yet completed the course.


About ten days after we got George, he developed cat flu. We still had George in isolation from the other cats so we thought they would be safe. However, Indie had sneaked into George's room once when I was feeding him (Indie will do anything for food) a couple of days before George went down with it, and of course she caught it too. It was a really awful time, we had the builders in putting a new roof on our house, two sick cats and we had to separate all four cats from each other.


Poor George was extremely ill, I really thought he might die (after all, he'd not long had surgery). We steamed him, and he was on antibiotics and eye drops, but even so it took two weeks before he was on the mend. But all Indie had was one runny eye (which admittedly was really yucky), so presumably her vaccinations had not protected her entirely but had certainly made it less unpleasant for her. Incidentally, Indie was better after three days.


So Indie and Harpsie are both infected. Although Harpsie does have flare ups occasionally, this does not seem to happen to Indie. However, she was left with runny eyes, which she had not had previously. Eyedrops and antibiotics clear these up beautifully, but as soon as we stop whatever treatment we are using, the runny eyes return.






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This page last updated: 10 February 2008


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I have tried very hard to ensure that the information provided in this website is accurate, but I am NOT a vet, just an ordinary person who cared for Harpsie with the help of qualified vets. This website is for educational purposes only, and is not intended to be used to diagnose or treat any cat. Before trying any of the treatments described herein, you MUST consult a qualified veterinarian and obtain professional advice on the correct regimen for your cat and his or her particular requirements; and you should only use any treatments described here with the full knowledge and approval of your vet. No responsibility can be accepted.


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