The blood is typically not where the virus or bacteria are concentrated. Also, "treating" the blood would also destroy red and white blood cells which we need

The blood is typically not where the virus or bacteria are concentrated. Also, "treating" the blood would also destroy red and white blood cells which we need to survive. ...not to mention the 10^6 other proteins, antibodies, and many unknown structures in the blood. ...things we'd be breaking that we don't even know what they do yet.