Flow diagram of the infection models for HPV (A) and chlamydia (B).

<p>HPV virions, <i>V</i>, only infect uninfected basal cells, <i>U</i><sub><i>b</i></sub>, to become basal infected cells, <i>I</i><sub><i>b</i></sub>. Since HPV is non-lytic, infected cells follow the typical epithelial life-cycle up to the surface passing through different life stages (parbasal <i>I</i><sub><i>p</i></sub>, differentiated <i>I</i><sub><i>d</i></sub>, differentiated at the surface <i>I</i><sub><i>s</i></sub>). Model <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1006646#pcbi.1006646.e007" target="_blank">3</a>. In the case of <i>C. trachomatis</i>, the elementary bodies, EBs, start the infection by infecting uninfected cells in the upper layers (<i>β</i><sub><i>u</i></sub> <i>U</i><sub><i>d</i></sub> <i>E</i><sub><i>u</i></sub> creates <i>I</i><sub><i>d</i></sub>). The EB populations start in the upper layers, <i>E</i><sub><i>u</i></sub>, and then migrate down, <i>η</i><sub><i>u</i></sub>, into the lower layers, <i>E</i><sub><i>l</i></sub>. As EBs migrate down layers they enter uninfected cells (<i>U</i><sub><i>b</i></sub> and <i>U</i><sub><i>p</i></sub>) and create infected cells (<i>I</i><sub><i>b</i></sub> and <i>I</i><sub><i>p</i></sub>) which die at rate <i>α</i> (boxes with square represent dead cells). The host immune response, <i>A</i>, is activated by infected basal cells in the case of HPV and all EBs in the case of <i>C. trachomatis</i>. Model <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1006646#pcbi.1006646.e008" target="_blank">4</a>. Note that for wart-associated HPV infections <i>ρ</i><sub><i>a</i></sub> = 0 and <i>α</i><sub><i>b</i></sub> = <i>α</i><sub><i>p</i></sub> = 1. See <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1006646#pcbi.1006646.t003" target="_blank">Table 3</a> for parameter descriptions and estimates.</p>