Direct contact is from a sick or carrier cat directly to another cat. In catteries, multiple cat households and shelters, the chance of this happening are high. As the disease progresses from cat to cat, multiple, repeated infections may occur so that each successive infection produces more virus in each individual. A cat coming in contact with these objects becomes infected indirectly rather than directly from the cat who put it there. People also spread this virus from cat to cat from their hands and clothing.
Indirect contact can be a source of infection in shelters, catteries or even veterinary clinics.
It is possible for a cat to get infected both directly and indirectly at the same time, especially when living or boarding in the same place for a period of time with the infective cat. Calici virus can survive in the environment for 8 to 10 days, making indirect contact equally important with direct contact as a source of infection. Infected kittens become sicker and shed more virus than adult cats. Accordingly, sick kittens are the worst source of infection to other kittens, who in turn will get even sicker and shed even more virus than the ones who gave it to them. Most veterinarians will diagnose FCV based on the clinical symptoms they see.