François-Xavier Weill and colleagues used expansive genomic data to chart the course of the seventh - and current - cholera pandemic throughout its most affected continent, Africa. Interestingly, Weill and colleagues say, their genetic timeline supports studies that link human-related factors to cholera transmission, rather than climate and environmental factors. Presenting their findings in a Report, the researchers have provided a detailed resource to inform future control of the disease. Though sometimes considered a disease of the past, cholera, an acute Vibrio cholerae infection that can cause a fatal loss of bodily fluids, continues to affect many regions of the world. The seventh pandemic of cholera began in 1961 and spread across South Asia, Africa, Latin America and the Caribbean, resulting in an estimated 21,000 to 143,000 deaths per year. Previous investigations into cholera propagation have fallen short of providing a complete picture of how the disease spreads across whole continents. Now, analyzing genomic data from 1,070 isolated Vibrio cholerae populations across 45 African countries over a 49-year period, Weill et al. show that the expansion of the seventh pandemic all sourced back to a single lineage - the El Tor strain - which was introduced (primarily from Asia) at least 11 times since 1970 into two main regions: West and Southeastern Africa, causing epidemics that lasted up to 28 years. What's more, the last five introductions into Africa involved multidrug-resistant bacterial sublineages, with the first resistant population found in the early 1980s. These resilient populations eventually replaced drug-susceptible cholera after 2000, which the authors hypothesize is connected to the mass use of various antibiotics during that time.
In a second and separate Report, Daryl Domman and colleagues studied the origin and spread of cholera in Latin America, where two of the largest cholera epidemics in the world have occurred, despite the fact that pandemic, or global, cholera was absent in the region for nearly 100 years. As such, tracing the disease's expansion in Latin America presents a unique opportunity to sort through both pandemic and local cholera lineages, and identify which are responsible for the two major cholera epidemics. Using whole-genome sequencing to characterize 252 isolated cholera populations across the Americas over a 40-year time span, Domman et al. found 164 strains were of the pandemic El Tor variety and 88 were distinct. The pandemic V. cholerae was solely responsible for both major epidemics, their analysis showed. By contrast, the local lineages identified - of which there were at least seven - were associated with disease characteristics distinct from those of pandemic cholera, for example, causing sporadic infections and short outbreaks rather than explosive epidemics, and only causing long-term, widespread illnesses when occupying environmental reservoirs (such as the Gulf Coast). By developing a better understanding of which lineages are responsible for specific patterns of cholera outbreaks, public health responses could be shaped to target epidemics more effectively, the authors say.