UC-Davis mounts investigation of rare calicivirus

UC-Davis mounts investigation of rare calicivirus

Oct 01, 2002

Los Angeles-A virulent, hemorrhagic strain of calicivirus ran through several practices in the L.A.-area like a brushfire and disappeared almost as quickly.

Close to 50 cats fell victim to the outbreak from early July to early August, and about one-half of those died as a result. The outbreak was traced to three veterinary practices in the area, and has opened up a new inquiry about this rare strain of calicivirus (FCV-Ari) at the University of California-Davis. Researchers want answers.

Dr. Kate F. Hurley, resident DVM at the Maddie's Shelter Medicine Program at UC-Davis' Center for Companion Animal Health, reports that by the time one practice identified this hemorrhagic strain, it had already swept through the entire hospital. In one hospital alone about 20 cats died from the viral strain. Drs. Janet Foley, Mike Bannasch and Hurley were running the scientific investigation.

The majority of the cats confirmed with the virus were also vaccinated, Hurley adds. The virus is believed to have originated in a rescue cat.

Presentation of FCV-Ari is different from field strain calicivirus, Hurley explains. Unique characteristics include facial, limb and generalized edema. Some cases have shown elevated bilirubin and some cats have become jaundiced. The mutant strains also cause a hemorrhagic-like fever in cats. Like the regular field strain of calicivirus, oral ulcerations were common with this strain as well as oral and nasal discharge. (See Table 1.)

Cats with mild signs recover within a few days, while cats with a severe case often die in spite of extensive symptomatic treatment.

Hurley says, "It is very different from what we usually expect from infectious diseases, targeting sick or weakened animals. If you have a big, robust and healthy cat that comes in contact with a little virus, it is usually not that big of a deal. Not with this."

Hurley adds that the virus can be transmitted very easily. In one case, the virus was believed to have been carried home on a veterinary technician's clothing and infected her cats.

FCV-Ari was first identified by Dr. Niels Pedersen, an infectious disease expert and director of the Center for Companion Animal Health at UC-Davis. Different outbreaks have spurred research ongoing at the University of Tennessee and Cornell University. This is believed to be the largest single outbreak ever reported.

UC-Davis researchers are conducting several different follow-up investigations on the outbreak, including genetic sequencing from samples of affected cats and follow-up viral cultures on some of the recovered cats to understand how long the virus is infectious. Detailed pathology, immunohistochemistry, detailed necropsies and electron microscopy work is also under way to understand the virus in infected tissue.

Hurley explains that from their work with necropsies, they have found lesions in the GI tract, liver, spleen, pancreas and lungs. But these lesions are not found consistently in these organs.

"In some cases, the liver was trashed, in other cases the livers were relatively unaffected but there were horrible ulcers in the GI tract," Hurley says.

Researchers want to know why.

Good news

The good news is the virus strain is self-limiting; in other words, it dies off fast. But when this virus is hot, it is tough to inactivate.

The virus can be shed in feces and in nasal, ocular and oral secretions.

"The virus can be very readily spread by fomites as well as direct transmission. It can be carried for at least several hours on contaminated hands, clothing, instrument, shoes, etc.," the university reports.

Droplet transmission is possible over 1-2 meters, while calicivirus can be carried through ventilation systems on dust and hair, airborne transmission over distances greater than a few feet has not been documented, the university adds.

How to kill it

Detergents alone won't kill it either.

"Standard hygienic practices that clinics employ may not be adequate to control this virus," Hurley explains.

When faced with an outbreak like this, bleach (5 percent diluted 1:32) is the most reliable disinfectant. One clinic shut down its cat admissions for an entire week to disinfect the premises.

UC-Davis recommends that contaminated exam rooms should be scrubbed down with the appropriate detergent and then disinfected with the bleach solution. If contamination is suspected, all surfaces should be thoroughly cleaned and disinfected, including offices and dog runs. The recommendation is to be very thorough too, including disinfecting telephones, keyboards, doorknobs and other frequently handled items.

If it can't be cleaned, officials recommend a quarantine of one to two weeks.

The university also makes these recommendations:

* Outpatient suspect cases (cats presenting with one or more of the signs described in Table 1) should be limited to one exam room, and protective garments should be worn when examining suspect cases.

* Cats presenting with only signs of upper respiratory infection, fever and/or oral ulceration are unlikely to be infected with virulent calicivirus, particularly if there is no history of likely exposure.

* Cats presenting with additional findings of icterus or oozing/crusting sores on the face or feet should be considered at moderate risk.

* Cats presenting with fever and facial or limb edema and/or a history of exposure to a diagnosed case of virulent calicivirus should be considered at very high risk.

* Hospitalized suspect cases should be housed in strict isolation, with separate equipment, gowns, gloves, caps and protective footwear used.

* Contact with affected cats should be kept to the minimum necessary to provide appropriate care, and should be limited to one or a few designated staff.

* Owner visits should be discouraged, and owners should wear protective garments when handling sick cats.