A person infected with Ebola is very contagious during the period they are showing symptoms. The CDC recommends casual contact and droplet precautions.

Note the following description of (casual) contact:

Casual contact is defined as a) being within approximately 3 feet (1 meter) or within the room or care area for a prolonged period of time (e.g., healthcare personnel, household members) while not wearing recommended personal protective equipment (i.e., droplet and contact precautions–see Infection Prevention and Control Recommendations); or b) having direct brief contact (e.g., shaking hands) with an EVD case while not wearing recommended personal protective equipment (i.e., droplet and contact precautions–see Infection Prevention and Control Recommendations). At this time, brief interactions, such as walking by a person or moving through a hospital, do not constitute casual contact.

(Much more contagious than an STD.)

But Lumifer is also correct. People without symptoms are not contagious, and people with symptoms are conspicuous (e.g. Patrick Sawyer was very conspicuous when he infected staff and healthcare workers in Nigeria) and unlikely to be ambulatory. The probability of a given person in West Africa being infected is very small (2000 cases divided by approximately 20 million people in Guinea, Sierra Leone and Liberia) and the probability of a given person outside this area being infected is truly negligible. If we cannot contain the virus in the area, there will be a lot of time between the observation of a burning 'ember' (or 10 or 20) and any change in these probabilities -- plenty of time to handle and douse out any further hotspots that form.

The worst case scenario in my mind is that it continues unchecked in West Africa or takes hold in more underdeveloped countries. This scenario would mean more unacceptable suffering and would also mean the outbreak gets harder and harder to squash and contain, increasing the risk to all countries.

We need to douse it while it is relatively small -- I feel so frustrated when I hear there are hospitals in these regions without supplies such as protective gear. What is the problem? Rich countries should be dropping supplies already.

Ebola is very hard to transmit person to person.

Um. Given that an epidemic is actually happening and given that more than one doctor attending Ebola patients got infected, I'm not sure that "very hard" is the right term here.

Having said that, if you don't live in West Africa your chances of getting Ebola are pretty close to zero. You should be much more afraid of lightning strikes, for example.