Almost all humans are chronically infected by one or more persistent viruses. Our understanding of the pathogenic processes of viral infection remains incomplete.
Infectious diseases cause a quarter of all deaths worldwide and one in five cancers. Certain viruses cause acute infections in humans, which can be rapidly fatal within days, for example influenza A and smallpox viruses. In contrast, other viruses are able to persist chronically in infected individuals, despite induction of an immune reaction (e.g. HIV, hepatitis and herpes viruses). Almost all humans are chronically infected by one or more persistent viruses. Our understanding of the pathogenic processes of viral infection remains incomplete.
In addition to facing a multiplicity of infection with exogenous viruses, all mammals, including humans, have a long-standing symbiotic relationship with a considerable number of microbial species, such as the microbiota and endogenous retroviruses (ERVs).
Recent evidence suggests that ERVs and other transposable elements actively shape gene transcriptional networks, responsible for cell identity. These networks can be responsive to environmental factors, exemplified by the response immune cells to infection. Correspondingly, ERV activity is also responsive to external factors, providing a potential link with disease development.