The Dynamics of EBV Shedding Implicate a Central Role for Epithelial Cells in Amplifying Viral Output

Abstract

To develop more detailed models of EBV persistence we have studied the dynamics of virus shedding in healthy carriers. We demonstrate that EBV shedding into saliva is continuous and rapid such that the virus level is replaced in ≤2 minutes, the average time that a normal individual swallows. Thus, the mouth is not a reservoir of virus but a conduit through which a continuous flow stream of virus passes in saliva. Consequently, virus is being shed at a much higher rate than previously thought, a level too high to be accounted for by replication in B cells in Waldeyer's ring alone. Virus shedding is relatively stable over short periods (hours-days) but varies through 3.5 to 5.5 logs over longer periods, a degree of variation that also cannot be accounted for solely by replication in B cells. This variation means, contrary to what is generally believed, that the definition of high and low shedder is not so much a function of variation between individuals but within individuals over time. The dynamics of shedding describe a process governing virus production that is occurring independently ≤3 times at any moment. This process grows exponentially and is then randomly terminated. We propose that these dynamics are best explained by a model where single B cells sporadically release virus that infects anywhere from 1 to 5 epithelial cells. This infection spreads at a constant exponential rate and is terminated randomly, resulting in infected plaques of epithelial cells ranging in size from 1 to 10 ⁵ cells. At any one time there are a very small number (≤3) of plaques. We suggest that the final size of these plaques is a function of the rate of infectious spread within the lymphoepithelium which may be governed by the structural complexity of the tissue but is ultimately limited by the immune response.

Author Summary

Epstein-Barr virus is a human pathogen associated with several human cancers that nevertheless persists benignly as a latent infection in the majority of adults. EBV persistence is characterized by the presence of latently infected cells in the blood and the shedding of virus into saliva. We present the first systematic quantitative analysis of virus shedding. We show, contrary to what was previously thought, that shedding is continuous and at a high level for all subjects tested. This constant presence of infectious virus may be a crucial risk factor in the development of the EBV-associated tumor nasopharyngeal carcinoma. Unlike infected cells in the blood, which are maintained at very stable levels for years, we show that virus shedding is highly variable such that at any time any individual may be a relatively high or low shedder. We have analyzed these dynamics mathematically and with a simple simulation model. We find that they can be explained by a simple exponential function which we hypothesize is the expansion of 1–3 plaques of epithelial cells.