The lead doctor in Sierra Leone in charge of fighting ebola himself got Ebola. If it's not that easy to contract ebola, you would have thought the foremost expert would have easily been able to avoid this.
Actually, you might expect him to be a lot more likely to catch Ebola. He's coming into deliberate vicinity of the virus on what one assumes is a weekly or even daily basis. Frequency effect is in play.
For similar reasons, you'd expect the world's foremost expert on avoiding shark attacks to be attacked by a shark more often than the general population. He's out there practicing his theories and doing his research every day. The rest of us aren't going in the water as often.
The best way to avoid being attacked by a shark in the ocean is not to go in the ocean. The best way to avoid contracting Ebola is to stay as far away from Ebola as possible. An expert might be better able to handle himself around Ebola, or around sharks, than the rest of us. But he's also more likely to be around Ebola (or sharks) in the first place.
Doctors are always at risk of exposure. If you deal with patients with virulent diseases all day long then that's equivalent to playing the lottery every day all your life.
All it takes is a single mistake, or one vector of transmission that was not yet known, or one patient sneezing at exactly the wrong moment or simply not having the tools and supplies to do the work safely.
Being a doctor in this field is a very high risk occupation, doing it in Africa is simply very brave.
