The tininess of Platt’s wound, in light of subsequent events, testifies that even a minuscule dose of an ebolavirus is enough to cause infection, at least if that dose gets directly into a person’s bloodstream. Not every pathogen is so potent. Some require a more sizable foothold. Ebolaviruses have force but not reach. You can’t catch one by breathing shared air, but if a smidgen of the virus gets through a break in your skin (and there are always tiny breaks), God help you. In the terms used by the scientists: It’s not very contagious but it’s highly infectious.
