An outbreak of what experts suspect is virulent systemic feline calicivirus, or VS-FCV, has led to the death of at least 65 cats at the Humane Society of Indianapolis, a private facility in the city that takes in an estimated 10,000 homeless animals annually.

News of the outbreak hit local media outlets on Monday, but veterinary experts stress that laboratory tests have not yet confirmed calicivirus infection (laboratory tests can not differentiate VS-FCV from the more common and less pathogenic, respiratory FCV). Results are expected later this week.

In the meantime, the Humane Society of Indianapolis has temporarily suspended all feline adoptions. The affected cats, which were euthanized, reportedly suffered severe oral ulcers, swollen limbs, crusting of the face, hair loss and fevers of up to 106 F. Some exhibited anorexia and early signs of pneumonia, an announcement on the shelter's Web site states.

Christine Jeschke, director of shelter operations for the Humane Society of Indianapolis, did not return phone calls from the VIN News Service seeking more information. Dr. Kate Hurley, program director for the University of California, Davis’ Koret Shelter Medicine Program, and veterinary epidemiologist Dr. Annette Litster, an assistant professor of Small Animal Internal Medicine at Purdue University and director of Maddie’s Shelter Medicine Program, are consulting on the outbreak.

Litster is careful not to speak about what’s going on in the facility due to privacy concerns but notes that almost all previously reported cases of VS-FCV have been associated with shelters. By contrast, outbreaks in veterinary medical facilities are much more rare, and previous outbreaks have burned themselves out within weeks due to the institution of strict infectious disease control and shelter management protocols, she says.

Hurley counters that while quick recognition, immediate and effective isolation and decontamination are important, such measures often are not enough to stave off an outbreak of VS-FCV, a virus known to cause subclinical infection and chronic shedding.

“I don’t know how often (outbreaks) happens,” Litster says. “There was a lot of literature on it for a while, but there haven’t been any cases written on it in the last couple of years. It’s not that it’s not happening, but one outbreak pretty much looks similar to another.”

Hurley doesn’t have a firm handle on how many cases have occurred in the United States, either, although she knows of about a dozen confirmed outbreaks. When it comes to VS-FCV, Hurley is quite possibly the nation’s foremost expert. She ranks as one of the first veterinary scientists to identify and track VS-FCV, which made its debut roughly a decade ago in a Sacramento, Calif. veterinary practice. Hurley, while in her residency in shelter medicine, watched the nation’s second known outbreak unfold in a Los Angeles shelter. There, she put her tools of outbreak investigation to work, tracing both the Sacramento and the Los Angeles incidents to shelter cats.

“We sampled a lot of healthy, exposed cats along with the sick ones, and what we found was that a lot more cats were infected than looked ill,” she recalls. “It’s not enough to control the cats that are symptomatic. You have to treat them all as though they are capable of transmitting the worst of this disease.

"This disease is so hard to manage effectively, it’s merciful that the virus tends to lose virulence over time because otherwise, it would be rampant," Hurley adds.

While that might strike alarm in some, Hurley is quick to warn veterinarians not to overreact. For starters, she considers VS-FCV to be extremely rare. And although calicivirus is highly contagious with the ability to survive for at least a month on just a few strands of hair, it’s not likely to turn up in average veterinary practices.

“If a cat walks in from an indoor-only home with no recent additions to the household, it’s possible, but unlikely,” says Hurley, speaking of VS-FCV. “It’s something that we can never simply relax about, but we need to keep it in perspective. Even if an outbreak is down the road from your facility, it doesn’t spread in your community unless there is intersection between your cat population and those infected.”

So what’s the difference between VS-FCV and traditional calicivirus? For starters, VS-FCV has a high mortality rate, although feline calicivirus strains vary in degree of virulence. Hurley's rule of thumb: “If it’s not bad, it’s not that." VS-FCV is a distinct syndrome characterized by vasculitis and consequent edema and skin ulceration. Pneumonia, hepatitis and sudden death can go along with it. VS-FCV strains attack the cells lining blood vessels, with affected cats exhibiting systemic vascular compromise and hemorrhagic-fever like signs, in part, due to viral invasion of epithelium and endothelium, coupled with host cytokine responses. 

That comes from a 2006 journal article co-authored by Hurley, which also pegs the mortality rate associated with VS-FCV as up to 67 percent in otherwise healthy adult cats. VS-FCV preferentially targets healthy adults, but it’s unclear why. Scientists suspect that the immune reaction itself is a disease component (J Feline Med Surg. 2006 Feb;8(1):55-61. Epub 2005 Oct 6).

According to Hurley, three factors must line up to birth a VS-FCV outbreak: the strain must be virulent, highly transmissible and resistant to commonly used vaccines (CaliciVax, manufactured by Fort Dodge Animal Health, does not target virulent calicivirus per se; it contains only one strain from one outbreak, which has never been documented before or since).

The trifecta doesn’t come easily.

"Not to be cavalier, but don’t assume that just because you have one case everyone will be infected,” Hurley says.

Why? Largely for the same reason that experts say the vaccine is not reliably effective, Hurley contends. VS-FCV is constantly mutating, so a viral strain that maintains all three elements for an outbreak is rare. Purdue’s Litster explains: “Calicivirus just isn’t very good at making copies of itself and makes slightly different versions all the time. Those different strains have different properties. There are hundreds of them.”

And just like influenza, it’s likely to stay one step ahead of the vaccines, Hurley adds. In a fact sheet on the Koret Shelter Medicine Program Web site, she explains that variant strains of FCV do not tend to remain stable within infected individuals or populations.

“Even in outbreaks of severe, vaccine-resistant VS-FCV, some cats can survive and continue to shed the virus. Some cats shed the virus for life, and as many as 50-percent of infected cats will shed the virus up to 75 days after their recovery from acute disease,” she writes. “These cats may transmit infection, but the risk greatly decreases once all clinical signs have resolved. While some recovered cats have been adopted to live in homes with naïve cats, there’s never been a reported case of recurrence of VS-FCV traced to any presumed carrier cat more than a month post recovery.”

That can make quarantining cats suspected of VS-FCV infection problematic. Still, rather than euthanizing suspected cases — a problem that Hurley says occurs when officials in shelters mistake VS-FCV for more common diseases, including run-of-the-mill FCV infection — she advises creating an immediate and complete break between exposed cats and those newly admitted if the resources permit.

Also, clean using soap and water followed by a bleach solution at a half-cup per gallon or potassium peroxymonosulfate. It’s a measure that’s good for guarding against the spread of calicivirus, even for veterinarians who might never see a case of VS-FCV infection.  
 
“One thing that’s important: Every time you handle a cat, use a disinfectant that kills calicivirus,” Hurley says. “The quaternary ammonium compounds that most practices use don’t kill it effectively.”