Can we make human plague history? A call to action

Plague is a communicable rodent-borne disease caused by Yersinia pestis, a Gram-negative bacillus member of the Enterobacteriaceae\ud family. As a zoonosis, plague is primarily a wildlife disease that occasionally spills over to the human population, resulting in seasonal surges in human cases and localised outbreaks. The predominant clinical form among humans is bubonic plague, which,\ud if untreated, has a lethality of 60%–90% but is readily treatable with antibiotics, reducing the death rate to around 5% if administered shortly after the infection. One to two per cent of all bubonic cases develop into secondary pneumonic plague, which in turn may be transmitted from person to person through respiratory droplets, producing primary pneumonic plague in close contacts.\ud Without antibiotic treatment, pneumonic plague is nearly 100% fatal, but early antibiotic treatment substantially improves survival. Today, Y. pestis is present in at least 26 countries, with more than 30 different flea vectors and over 200 mammal host species. Although human plague cases continue to be reported from Asia and the Americas, most cases currently occur in remote, rural areas\ud of sub-Saharan Africa, mostly in Democratic Republic of Congo and Madagascar (around300–500 per year). However, large-scale\ud transmission may also occur. During the 14th century, the Black Death, caused by Y. pestis, is estimated to have killed 30%–40% of the European population. It is important to emphasise that human\ud plague is mostly a poverty-related disease. Therefore, given that population density and the absolute number of people living in extreme poverty are both increasing in sub-Saharan Africa, there is no likelihood of plague being eliminated as a public health threat in the foreseeable future. However, the WHO does not consider plague to be either a neglected tropical disease or a ‘priority pathogen’ that poses a public health risk because of its epidemic potential. In September 2017, an unprecedented urban outbreak of pneumonic plague was declared in Madagascar, striking primarily its capital Antananarivo and the major seaport of Toamasina. This episode once again brought international attention to plague, reminding\ud us of the capacity for human plague to spread in urban settings and cause substantial societal and economic disruption. This should\ud raise alarm bells that a research agenda is needed.