The role of nutrition in infectious disease has long been associated with changes in the immune response of the nutritionally deficient host. It has been shown in a number of studies that nutritionally deficient humans or animals are more susceptible to a wide variety of infections. This increase in susceptibility is thought to be the result of an impaired host immune response due to a deficient diet.
However, recent studies have demonstrated that not only is the host immune response affected by the deficient diet, but the viral pathogen itself can also be altered. Dietary deficiencies that lead to oxidative stress in the host [e.g., selenium (Se) deficiency] can alter a viral genome such that a normally benign or mildly pathogenic virus becomes highly virulent in the deficient, oxidatively stressed host. Once the viral mutations occur, even hosts with normal nutriture can be affected by the newly pathogenic strain.