West Africa has been affected by an epidemic of Ebola of unprecedented magnitude. Since summer 2014, we have been working very closely with Amadou Sall and his team from Institut Pasteur Dakar and a number of local partners to better understand the complex epidemic dynamics of Ebola, evaluate the impact of control measures and assess insights we can gain from data routinely collected during the epidemic. Amadou Sall and his team have been running the diagnostics laboratory in Conakry, the capital city of Guinea, for the whole duration of the epidemic.
An important focus of our research on Ebola is to better characterize the transmission of the virus. Such insight is critical to inform decisions about optimal use of resources. For example, in a context where resources are limited, is it better to increase infection control at funerals or to shorten the delay from symptom onset to isolation of cases? To answer these questions, we reconstructed chains of transmission of Ebola in Conakry, the capital city of Guinea (Figure 1). The study, published in Lancet ID , made it possible to characterize the contribution of the different routes of transmission (funerals, hospital, community) to the overall epidemic and to ascertain the impact control measures had on transmission. We concluded that in Conakry, early interventions had the potential to stop the epidemic but reintroductions of the disease and lack of cooperation of a small number of families led to prolonged low-level spread, highlighting challenges of Ebola control in large urban centres. We are currently extending these analyses to try to better understand the puzzling epidemic trajectory of Ebola in Guinea and explain how Ebola managed to be maintained for so long in the country.
Figure: Transmission tree of Ebola virus. Dates of symptom onset are indicated in the circles for cases that infected more than 3 persons. The size of the circles is proportional to the number of persons infected by the case. © Institut Pasteur
 Faye O, Boëlle PY, Heleze E, Faye O, Loucoubar C, Magassouba NF, Soropogui B, Keita S, Gakou T, Bah EHI, Koivogui, Sall AA, Cauchemez S. Chains of transmission and control of Ebola virus disease in Conakry, Guinea, in 2014: an observational study. Lancet Infectious Diseases 2014; online publication.