This can vary from a few mild symptoms, all of the above, or anywhere in between. The healthier a cat is, the better the natural immune system will be able to work to fight infection. The virus can make an unhealthy or stressed cat very ill, while it may just depress and cause mild symptoms in a healthy one. The better the state of nutrition, the better a cat will be able to fight the disease. An example of physical stress might be a pregnancy, while emotional stress could be a cat show or a visit to the vet.
All cats have an inherent immune system.
It is difficult to explain how this relates to disease, but it has been proven that certain pedigreed cats are more prone to some diseases than others. The larger the population in a given environment, the more susceptible these cats will be to respiratory disease. Latent is the term used for the presence of a disease organism that is not causing the disease at that particular time in that particular individual. Cats in the latent phase only have the virus internally, but feel normal and do not shed the virus to other cats and the environment. One week is the usual time frame from the triggering event to the production of active, shedding virus and possible illness.