Epstein-Barr Virus (EBV) DNA as a Potential Marker of in vivo Immunity in Professional Footballers.

Introduction: Team sport athletes have increased susceptibility to upper respiratory symptoms (URS) during periods of intensified training and competition. Reactivation of Epstein-Barr Virus (EBV) may be a novel marker for risk of upper respiratory illness (URI) in professional athletes. Aims: To investigate changes in salivary EBV DNA (in addition to the well-established marker, salivary secretory immunoglobulin A), and incidence of URS in professional footballers. Methods: Over a 16-week period (August to November 2016), 15 male players from a professional English football League 1 club provided weekly unstimulated saliva samples (after a rest day) and recorded URS. Saliva samples were analyzed for secretory IgA (ELISA) and EBV DNA (qPCR). Results: Whole squad median (interquartile range) saliva IgA concentration and secretion rate significantly decreased (p < .05) between weeks 8 and 12 (concentration, 107 (76-150) mg/L healthy baseline to 51 (31-80) mg/L at week 12; secretion rate 51 (30-78) µg/min healthy baseline to 22 (18-43) µg/min at week 12). Two players reported URS episodes during week 10, both after IgA secretion rate decreased below 40% of the individual's healthy baseline. EBV DNA was detected in the weeks before URS but also at other times and in healthy players (overall frequency 40%, range 11-78%) and frequency was similar between the URS and healthy group. Conclusion: These findings confirm salivary IgA as a useful marker of URS risk but EBV DNA was not. Further research capturing a greater number of URS episodes is required, however, to fully determine the utility of this marker.