It would depend when and how the body fluid is applied. I have no idea how to make a bomb, and how it would/could work. But lets say, for the sake of the argument, that this explosive device contains small packets of infected blood, instead of, as you may stipulate, blood being smeared over the outside of the device. Now, the shrapnel will inflict open wounds. The packets will burst open, infected blood will come in contact with the wound.... I question if the little heathens came up with the idea themselves, or if someone suggested it.