Lessons learned? Ebola, dietary salt reduction and epigenetics

TIME Persons of the Year 2014 were the Ebola fighters who worked with few resources at considerable personal risk and saved lives. Jeremy Farrar, director of the Wellcome Trust, wrote of Ebola in 2014, ‘It is still a matter of quarantine and safe funerary practices: shut you away and bury you nicely. These remain the most effective public health tools we have, but also the bluntest and most brutal. Can it be right to rely on them still?’ A year later, he announced in triumph the news of an effective Ebola vaccine. Developing and mounting a vaccine trial during the worst-ever Ebola outbreak is a staggering achievement itself—and an efficacy of 100% is truly remarkable. More reliable estimates using complete data and per-protocol analyses will be published in due course. A systematic review of risk factors for transmission of Ebola published in this issue found that caring for a case in the community, especially until death, and participation in traditional funeral rites were strongly associated with acquiring disease. These findings provide support for the current Ebola vaccination strategy used in Guinea. There is no shortage of lessons learned from the recent Ebola epidemic—including the need for reforms in rapid response capability, research, leadership and better governance. But the importance of disease mapping appears to have been overlooked in the dialogue on Ebola. In this issue, Tom Koch, medical cartographer, poses this question: ‘How did many of the best minds in infectious disease, epidemiology and disaster medicine miss the early spread of the filovirus from a remote village in Guinea until its presence became regionally epidemic?’ The answer is that people living in remote villages where Ebola was first diagnosed are highly mobile. Quarantine measures— the only effective prevention strategy—were not used in villages and towns linked by patterns of travel to Ebola villages. Early proposals for containing the Ebola epidemic made no mention of mapping, and mathematic models assessing outbreak potential ignored the spatial dimension, assuming ‘that hosts mixed randomly both in the community and hospital’. Mapping of Ebola focused largely on producing incidence maps which were site specific and could not give predictive information on likelihood of spread to other places. Koch makes several proposals, including use of origin-destination maps of travel patterns of exposed and sick people, augmented with vector environmental factors where feasible, to assess the risk of spread and possible quarantine of villages and towns: essential reading for planning responses to the next viral epidemic. Lessons can be learned from a review of the evidence for and against population-wide reductions in dietary salt— sometimes dramatically termed ‘salt wars’. Trinquart and colleagues conducted a ‘meta-knowledge’ analysis—a twostep process: first, examining the patterns of citation in relevant reports; and second, assessing the agreement in primary study selection in systematic reviews. The authors’ aim was to understand how the salt controversy has been sustained (over two decades) and explore how the beliefs or prejudices shape knowledge production. The idea of exploring citation bias is not new. Studies reporting small effects of salt reduction on blood pressure were cited much less often than one that demonstrated effects about 10 times greater (see Figure 1). This review included non-randomized studies, which exaggerated the apparent blood pressure reduction. Over the longer term, this citation bias has weakened (see Figure 2) but it is notable that this review is still being cited, probably because it was published in the British Medical Journal, perhaps taken to suggest higher quality research and being easy to find.