Well I read a billion of them can fit into a centimeter drop of blood which sounds pretty damn small to me. Plus these nurses in Dallas who got it, they said only their neck was exposed, so what did this guy Thomas Duncan do, sneeze on their necks and then they rubbed their necks with their hands and put it in their mouths? Maybe, but I tell you that sounds pretty unlikely. Aren’t they completely disinfected from head to toe then they take a shower? This is two nurses who got infected from this guy.
A centimeter of blood is about 1 ml, or about 1/5 of a teaspoon. That is a huge volume compared to a droplet. Droplets are tiny, about the size of the period at the end of this sentence.
The Ebola virus can enter through a break in the skin, even if the break is too small to be seen. If their necks were bare (and that is a detail I have not seen elsewhere), they could have splashed tiny droplets onto their skin doing any number of things—cleaning up vomit or diarrhea, changing soiled sheets or patient clothing, etc. They might have even unthinkingly reached up to scratch an itch with contaminated gloves. It only takes one such occurrence, one droplet full of a few dozen viruses landing on a tiny unseen break in the skin, to cause an infection. Or they could have contaminated themselves during the PPE removal, which is an exacting process that is difficult to perform properly (and they were untrained; I have not verified, but another poster said that they had read the CDC guideline—reading does not substitute for hands-on training).