Humans with low blood selenium concentrations are more likely to have impaired immune function and rapid mutation of benign variants of RNA viruses to virulent forms, e.g., in HIV infections. Low blood selenium concentrations are concentrations less than 1 micromol of selenium per liter of blood = less than 78 micrograms of selenium per liter of blood [Harthill].
If a virus-infected, selenium-deficient human host is supplemented with selenium, the mutation rate of the virus tends to decrease, and the immune function tends to improve [Harthill].
Thus, the selenium status of the human host can have a profound effect on the development of a virus infection. In cases of selenium deficiency, a normally non-virulent virus can become virulent. A virus can become pathogenic by replicating in a nutritionally deficient human host [Beck].