One of the most recent mysteries of Ebola is the recent re-establishment of the disease in Liberia, which had rid itself of the disease months earlier. This cluster of 3 infections was puzzling as the index case was a 15 year old boy who had no known contact with Ebola patients.
Further investigation revealed that the boy's mother had antibodies to the virus yet was never noted to be an Ebola case -- she likely represented the rare occurrence of a minimally symptomatic Ebola patient. Her uncle had succumbed to Ebola in July 2014 and likely passed it silently to his sister.
So what happened in the ensuing 4 months? One hypothesis is the mother became pregnant. Pregnancy is a well-known to be associated with diminished immune system function (e.g. pregnancy and severe influenza) and possibly lurking remnants of Ebola, freed from total immune surveillance, begin to stir again and reached levels sufficient to infect the boy. This asymptomatic shedding of Ebola has been reported in other pregnant women who, in most circumstances, are considered at higher risk for severe Ebola. The mother, with her antibodies and her genetics (which protected her the first time), had no outward symptoms.
When the origin of this transmission is hopefully definitively established through genetic sequencing of the viruses, it will provide much insight into the residual risk of transmission that there may be from Ebola survivors. While it is known that sexual transmission from males is possible up to 6 months from recovery, the other Ebola sanctuaries (Dr. Ian Crozier's eye, Nurse Pauline Cafferkey's central nervous system) have not yet been linked to transmission. Another important question will revolve on understanding just who has subclinical infection and who has persistent virus.
Elucidating these risks in more detail will influence how Ebola vaccination is used to protect those not just in contact with active cases, but those in contact with recovered cases.