I can think of a number of symptoms that a passenger travelling from that part of the world might exhibit that would be cause for concern and likely require input required from Port Health. Some of the illnesses that I've had to deal with onboard on flights from West Africa to the UK include Malaria, Yellow Fever, Lassa Fever, as well as (deaths) from Cocaine smuggling (drug mules)... and of course there's even a possibility of Ebola.