Adding to the danger , doctors may mistake the initial stages of an Ebola infection for another , milder illness . Aid worker Nancy Smith becomes second American infected . Doctor John Brantly is ill after treating Ebola patients in Liberia last week . The current outbreak of the virus is the deadliest ever , health officials say . A doctor working on the Ebola outbreak in Sierra Leone is also infected .
Aid worker Nancy Smith becomes second American infected . Doctor John Brantly is ill after treating Ebola patients in Liberia last week . The current outbreak of the virus is the deadliest ever , health officials say . A doctor working on the Ebola outbreak in Sierra Leone is also infected .