[SS15] Next-Generation Mathematical Biology: Where It Meets AI

[SS15-04] The timing and frequency of cellular co-infection with HSV

David A. Swan¹, Shadisadat Esmaeili¹, *Josh Schiffer¹, Marius Walter¹ (1. Vaccine and Infectious Diseases Division, Fred Hutchinson Cancer Center (United States of America))

Keywords:

Virology,Herpes,Recombination,Mathematical model

The epidemiologic importance of HSV recombinant viruses is highlighted by their high global frequency. Cellular co-infection with two separate viral strains is a pre-requisite for recombination and infection conditions which support co-infection are important to define. We applied spatial agent-based mathematical models which capture viral replication, spread, and protein expression at the single cell level to experimental data tracking CFP (cyan fluorescent protein) and YFP (yellow fluorescent protein) labelled HSV-1 in A549 lung epithelial cells following infection at low multiplicity of infection (MOI), and longitudinal measures of HSV DNA in and outside of cells. In this system, co-infected cells express both fluorescent proteins at significant levels. Experiments and modeling were also performed using viscous and liquid media to compare rates of HSV cell-to-cell versus cell-free spread. We tested various models assuming competing hypotheses. The optimal model precisely recapitulated cell-associated and cell-free HSV DNA levels; numbers of cells with cyan, yellow and dual fluorescence; overall levels of fluorescence in those cells; and morphology of observed viral plaques. The frequency of initially co-infected plaques exceeded the product of the CFP and YFP MOI, implying that certain cells were especially susceptible to co-infection. Optimal fit to the data was also predicated on HSV superinfection occurring early during the eclipse phase before an infected cell is producing virus. This co-infection window lasted for 2 hours, after which cells efficiently restricted super-infection. In viscous media, cells expressing the two fluorophores were mostly restricted to the boundary of colliding CFP and YFP plaques. In liquid relative media, cell-associated and cell-free HSV DNA levels, as well as numbers of cells with cyan, yellow and dual fluorescence, were higher after 12 hours due to rapid cell-free HSV spread from supernatant to susceptible cells, leading to higher levels of co-infection overall. Our results demonstrate that co-infection is restricted to the early eclipse phase after which superinfection exclusion predominates and when plaques with different viruses collide. Both processes likely represent significant bottlenecks to HSV recombinant formation in humans.