This is where the virus usually causes a lesion by cell necrosis, e.g. canine parvovirus in the gut epithelium.

The main target organ is often given in the name of the virus.

5) Excretion during incubation, disease and at a low level in the recovered animal for weeks or months e.g. canine adenovirus. The virus can then be spread by contact, aerosol or on objects.

6) Latency.