Hi Hip,
Since you are very interested in the study of minerals in human Biochemistry, i have another explanation for the anti-viral effect of Selenium in muscle tissue such as heart tissue, or in Organ tissue such as Liver and Kidneys. All of these organs have a very high tissue concentration of Selenium in the healthy human being as compared to normal tissue concentrations. The microbiologists have linked the anti-viral behavior of this Selenium by theorizing that the Glutathione Peroxidase is responsible for damaging the virus as it attacks the heart muscle tissue. The first evidence for the role of Selenium in human biofiunction was the discovery that Keshan disease, a viral infection of heart tissue, was caused by extra low levels or depleted levels of Selenium in human heart tissues at Keshan province in the 1970's in China. The deeper root cause was that the Keshan Province soil and water was highly depleted in Selenium. The lack of Selenium in diet caused many residents to have viral infections of the heart tissues leading to death.
My view is the following: For all of these highly critical organs the human body must protect its crown jewels, the organs by every possible method from attacks of Bacteria and Viruses of all types throughout the human lifetime. To be able to resist these microorganisms, these specific organ tissues cells purposely seek out and incorporate from the bloodstream higher amounts of Selenium which is normally circulating in the blood.
The higher tissue cell concentration of Selenium then acts as a Shield that is both anti-viral and anti-bacterial as the viruses for example cannot survive living in such cells with SE, since this mineral is a Poison to the viral biofunctions. For the same reason you will find another very critical mineral Copper CU being utilized and incorporated at very high concentration in the Organ tissues as Copper is another mineral poisonous to Bacteria and Viruses. This is a second part of the Mineral Defense Shield that is incorporated into the cellular structure. These two minerals concentration in humans vary depending upon how much was ingested from human nutrition as they are both rare minerals. This means that in the majority of foods, a trace amount is found. To this day their full role has still not been adequately understood for their highly critical functions.
All of these minerals are best utilized in their organic form as this maximizes their absorption into tissue. For example, the organic copper is very healthy to human tissue while the mineral copper when ingested from say copper piping is a pollutant to the body and unhealthy. The human body does not want minerals in the mineral form; it needs minerals incorporated into an Organic structure to be properly absorbed as you know. Taking them in their Organic form means taking them from plants which have already converted them from mineral form in the soil, into an organic structure in the leaves, root, or seeds [Brazil nut is a seed]. Another source is to obtain such minerals from Animal sources such as the Liver which acts as a storage in the Animal body for Copper and some other minerals.
Abdulrahman