Within-host infection models
Within-host models describe infection processes inside an individual rather than transmission between individuals in a population.
Target-cell model
A standard viral model uses target cells \(T\), infected cells \(I\) and free virus \(V\):
\[\frac{dT}{dt}=-\beta TV,\]\[\frac{dI}{dt}=\beta TV-\delta I,\]\[\frac{dV}{dt}=pI-cV.\]Here \(\beta\) controls infection of target cells, \(\delta\) infected-cell loss, \(p\) viral production and \(c\) viral clearance.
Extensions
Immune responses, drug treatment, latent infection and multiple target-cell types can be incorporated when required by the biological question.
Scale distinction
Within-host viral load can influence infectiousness, but within-host and population-level epidemic models operate at different biological scales.
Key idea. Within-host models study pathogen replication and host response inside one organism, complementing population-level epidemiological models.