Calicivirus is one of the most common cat diseases responsible for oral and upper respiratory infections. After being exposed to the virus, cats may go through an incubation period of 2 – 6 days before displaying symptoms. The infection can last anywhere from 2 – 3 weeks, during which the infected cat will shed the virus. It can most easily spread to other cats via sneezes. Calicivirus might also be present in the infected cat’s urine or feces, but this usually isn’t how it spreads. Still, it’s very easy for calicivirus to spread among cats in shelters, vet clinics, and other gathering places. It can even be spread by humans who pet a sick cat.