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Should You Vaccinate Your Cat Against Feline Calicivirus?

By Darcy Lockman

Should You Vaccinate Your Cat Against Feline Calicivirus?

One day, Jeanne Prins' six-month old kitten Paris was playing actively; the next she was like a limp rag. "I took her to the veterinarian," recounts Prins. "We assumed it was an abscess. He gave her a shot and said to bring her back on Monday if she wasn't better. I took her home and she couldn't stand up. On Sunday morning, my 20-year-old cat Sanibel couldn't walk. I assumed it was coincidental. But then on Monday, my one-year-old cat, Higgins, also couldn't walk. My 10-year-old cat, Kitten, stopped eating and I took him in, too. Then A.J. couldn't climb the stairs. The virus hit us like a tornado."

Prins, a veterinary supplies salesperson from Reisterstown, Md., discovered last November that she ultimately lost three cats to what was confirmed, upon autopsy, to have been a virulent systemic strain of the feline calicivirus. Two of her cats, Paris and Higgins, survived the illness, while the five others never showed a single symptom. Prins is now an active advocate in her community for vaccinating against the illness.

Tough to Target
The sickness is called virulent systemic feline calicivirus (VS-FCV). Thanks to the efforts of Prins and other concerned pet owners and researchers, a new vaccine is available against VS-FCV, a potentially fatal mutation of the feline equivalent of the common cold. Similar to preventing human flues and viruses, however, targeting this illness can prove difficult.  

It is not unusual for your feline to feel under the weather every so often. Upper respiratory infections, oral ulceration, limping and lethargy occur fairly frequently in cats, and may be symptoms of the very common feline calicivirus (FCV). According to the Center for Companion Animal Health at the University of California's Davis School of Veterinary Medicine, up to eight percent of house cats and 25 percent of cats from multiple cat environments like shelters are calicivirus carriers at any given time. The virus is most often fairly harmless. A few days of rest and your cat should be back to its old self.

More Dangerous Forms of Calicivirus
Some strains of the constantly mutating calicivirus cause the symptoms mentioned above. As in the case of Jeanne Prins and her kitten, certain types of the virus cause no symptoms at all, while other more infrequently occurring strains become highly virulent and dangerous. The virulent and non-virulent forms of calicivirus can both begin with the same symptoms -- including the aforementioned oral ulceration, limping and fever. However, unlike the more common strains of FCV, VS-FCV can progress in some cats to more severe problems, including limb swelling, hair loss, ulceration and oozing of the skin, and even death. Outbreaks of VS-FCV in any cat community are very rare. More commonly, cats experience this severity of symptoms due to common FCV combined with panleukopenia or another respiratory issue.

Documenting numbers of cases has proven difficult, since over 65 feline caliciviruses exist worldwide. Recently outbreaks of the deadly version of the virus, however, have been reported in Northern California and New England. One strain appears to be particularly fatal to cats housed in animal shelters.

An insidious feature of FCV, including the virulent forms, is that it spreads easily. Cats may shed the virus through their saliva, so a single sneeze could blast other felines with it. Even asymptomatic cats could harbor the virus and then pass it on to others. If your cat is ever diagnosed with any type of calicivirus, be sure to quarantine it from other animals. Other species, like raccoons, can get it too.

To Vaccinate or Not to Vaccinate?
As with any vaccine, however, there are pros and cons when it comes to administering it to your cat. The major con arises largely from the fact that this vaccine is a "killed vaccine," which means that additional chemicals are needed to stimulate the vaccine's immune response. There is some theoretical but to date unproven concern that these chemicals might predispose cats to injection site tumors. The major pro, of course, is that the vaccine may protect your cat against a potentially life-threatening disease.

Veterinarian Kate Hurley, an assistant clinical professor at California's UC Davis School of Veterinary Medicine, studies all forms of the calicivirus. She offers the following thoughts:

  • VS-FCV is a rare mutation of feline calicivirus that is a serious threat when it emerges. However, it is uncommon. VS-FCV emerges and resolves spontaneously. This is because the calicivirus is an unstable virus, which means it mutates every time it is passed from one cat to the next. So every calicivirus that mutates into a virulent calicivirus will, as it is passed on to the next cat, ultimately once again become a non-virulent calicivirus.
  • Because the virus is always mutating, there is no single virulent strain to vaccinate against. While the new vaccine may provide broader protection against calicivirus in general, it is not certain that it will protect against another virulent strain.

The Bottom Line
"If I were already getting my cat vaccinated with a killed vaccine, I would add the new strain. There might be benefits, so why not?" says Dr. Hurley. "But I wouldn't switch from a vaccine I was already happy with, [such as] a nasal spray or modified live vaccine, to get the benefit of the protection which there may or may not be. I would not panic in the face of a reported outbreak and rush to get my cat vaccinated. The place your cat is most likely to pick up the virus is at the vet. Wait for the crisis to pass, and have your cat vaccinated in its usual series, adding the new vaccine strain if you choose."

Protecting your cat's health always involves a series of choices. The same is true when dealing with concern about virulent systemic feline calicivirus. Consult with your own veterinarian about the issue to decide what could be best for your cat.

Darcy Lockman is a Brooklyn, N.Y.-based freelance writer and frequent contributor to The Daily Cat. Her work has appeared in publications such as the New York Times and Rolling Stone.


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Posted on July 17, 2008

jeanette says: Hi, I have a 3yr old feline cat and a 4yr feline cat. Both have been neutered but not vaccinated. Are they too old to be vaccinated now?

Posted on November 11, 2008

Chris Carlson says: I had my cat vaccinated for this a few days ago at the reccomendation of my vet during my cat's annual exam. My cat is now sneezing alot during the past 2 days. Is this something to be concerence about? He has to go in again in 2 weeks for the booster.

Posted on April 23, 2009

Marian says: My three year old cat just recently passed away. I believe she had this virus. Her brother seems healthy enough. They used the same bowls for eating and drinking. Thank you for the information.

Posted on April 13, 2008

Shirley U says: my cat , out of the blue, is running a temp, laying around and not feeling well. Nose is dry and hot. ate a few bites of food this am, but laying around and feeling bad. nose is hot and dry.

Posted on June 21, 2008

Ronda says: I'm shocked by the number of people posting to this site with sick cats. You need to take a cat who is feverish, not eating, not drinking or has bloody stool or signs of any kind of illness or infection to a vet. Don't just post on a website!

Posted on January 9, 2008

Bea's Mom says: If a woman had a histeroctomy (I don't know the correct spelling)... she would take hormones or have her body thrown into shock. What happens to a young cat's body when she's spayed?

Posted on February 2, 2008

Melissa says: I recently had the same issue with this virus. I took my strictly indoor cat in to the vet and came home with this virus which killed 2 out of my 3 cats. This virus is horrible and both cats suffered until I had to have them put down. Within 2-3 days my younger more healthy cat had bleeding ulcers on his face. I turly think that my cat Bella brought it home from the emergency vet and spread it to Nikko. My eldest was the only survivor, he is 11 years old. PLEASE vaccinate against this disease especially if your cat visits the emergency room for other things. It really is a very bad virus.

Posted on October 5, 2007

caitlyn says: i liked the article. it should tell more about the cats. it really informed me

Posted on November 4, 2007

Ashley Pinto says: My cat simba is a nine years old. Hes very hyper like a kitten.But sometimes hes not feeling well.Onetime, I mistakenly left the cabinet door to his litterbox closed . So he pooped on the floor. When I came home his poop was bloody...? help...?

Posted on November 30, 2007

Nadine Burge says: This was informative. However, in case of a local outbreak, it doesn't hurt to be careful and have your pets vaccinated. THe alternative is much worse.

Posted on December 14, 2007

sandy says: my kitten of 6 months is tired, sores on tongue, inactive. its been going on for three days now. could this calicivirus be it? but he is eating and drinking some.

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