<unk>  is the study of the process and mechanisms by which viruses cause diseases in their target hosts, often at the cellular or molecular level. It is a specialized field of study in<unk> ogy.<unk>  is a qualitative description of the process by which an initial infection causes disease.<unk>  disease is the sum of the effects of<unk>  replication on the host and the host's subsequent immune response against the virus. Viruses are able to initiate infection, disperse throughout the body, and replicate due to specific<unk> ence factors. There are several factors that affect<unk> . Some of these factors include<unk> ence characteristics of the virus that is infecting. In order to cause disease, the virus must also overcome several inhibitory effects present in the host. Some of the inhibitory effects include distance, physical barriers and host defenses. These inhibitory effects may differ among individuals due to the inhibitory effects being genetically controlled.<unk>  is affected by various factors: (1) transmission, entry and spread within the host, (2) tropism, (3) virus<unk> ence and disease mechanisms, (4) host factors and host defense.
Viral pathogenesis
Opportunistic infection
Introduction to viruses
Human pathogen
Pathogenic bacteria
Virus latency
Blood-borne disease
Parasitism