And are there any research papers of models of this? Thoughts: How many pathogens are needed to cause a full-blown infection? A single disease pathogen, for example, is virtually harmless. But is there a critical value of the number of disease pathogens that are needed to cause an illness? And once that critical value is reached, is the severity of the illness related to the concentration of pathogens in key regions? Does the concentration of pathogens usually vary from illness to illness? (depending on onset of immune system response and on "resources" that the virus can exploit?) Are there any resources I could consult regarding the pathogenic concentration of an illness plotted as a function of time?