A shadow is a surface light cannot touch or reflect off of. Usually shadows appear when the main object is covering a light source. For example, lunar eclipses. Lunar eclipses cause a shadow over Earth because they block the main light source, The Sun from our point of view, casting a giant shadow over Earth.
The Marburg virus wasn't mutating this early on, therefore the Coronavirus is much more deadlier and almost impossible to get a cure for, due to the rapid change in pathogens!
