I have this hypothesis that one day we will discover that a major vector of disease has been at play due to having blood exposed to the external environment where it could be read by all kinds of pathogens encountering a weaker/dormant part of the human immune system
I further believe that this is how viruses learn to infect a new host or jump species..

I can't disprove to myself because I know jackshit about immunology/biochemistry and I should be ashamed for making this post. Thank you for your time