Epidemics of plague past, present, and future
Authors: Paul Mead
Journal: The Lancet Infectious Diseases (2019)

Plague has a deservedly bad reputation. The disease killed over 20 million people in India during the early 1900s, and even more people during the so-called Black Death that swept Europe beginning in 1346. The causative agent, Yersinia pestis, circulates on five continents, infecting a range of animal reservoirs living in diverse ecological settings. Human disease is typically acquired through flea bites and takes the form of bubonic plague; however, infection can also spread to the lungs, producing pneumonic infection. Pneumonic plague is rapidly fatal and can spread from person-to-person through respiratory droplets. In 1910, an outbreak of pneumonic plague in Manchuria killed nearly 60 000 people in just 7 months.1Wu LT Chun JWH Pollitzer R Wu CY Plague.A manual for medical and public health workers. Mercury Press, Shanghai1936Google Scholar Understandably, it was with some alarm that health authorities reported an outbreak of pneumonic plague in September, 2017, in Antananarivo, the capital city of Madagascar. Antananarivo is home to more than 2 million people, densely packed and largely impoverished, with little public-health and health-care infrastructure. A large and complex response was mounted with the assistance of the international community and 2 months later, on Nov 27, 2017, local health officials declared the outbreak contained.2WHO Regional Office for AfricaPlague outbreak Madagascar. External situation report 14. Dec 4, 2017.https://apps.who.int/iris/bitstream/handle/10665/259556/Ex-PlagueMadagascar04122017.pdf;jsessionid=A7C3E09AB131ED62DBB2891D2E3BBC0B?sequence=1Date accessed: November 30, 2018Google Scholar The immediate danger had passed; however, the risk of future outbreaks remains, and it is important to learn all that is possible from this event. In The Lancet Infectious Diseases, Rindra Randremanana and colleagues3Randremanana R Andrianaivoarimanana V Nikolay B et al.Epidemiologic characteristics of urban plague epidemic in Madagascar, August–November, 2017: an outbreak report.Lancet Infect Dis. 2019; (published online March 28)http://dx.doi.org/10.1016/S1473-3099(18)30730-8Summary Full Text Full Text PDF PubMed Scopus (65) Google Scholar report a detailed, systematic analysis of this exceptional outbreak of pneumonic plague in an urban setting. The authors should be commended for their diligence—this assessment required refining diagnostic protocols, retesting samples, and reclassifying cases. Along with other important findings, the analysis revealed that the outbreak was considerably smaller than initially feared. Among 1878 clinically suspected cases of pneumonic plague, nearly all of which received laboratory testing, only 32 (2%) were laboratory confirmed as plague, with eight (24%) of these leading to death. Another 386 (21%) cases were classified as probable plague, but only a portion of these are likely to have been true infections. Given the circumstances, it is natural to assume that this outbreak was comprised of one or two extended chains of person-to-person transmission. However, considering the smaller number of cases and their distribution over time, it is possible that the outbreak was in fact a series of small clusters and individual pneumonic cases arising independently from bubonic infections. Aided by molecular tools, investigators have found an alternative framework for zoonotic diseases, in which outbreaks result from simultaneous spillover of multiple strains from the environment rather than extensive transmission of a single clone.4Petersen JM Carlson JK Dietrich G et al.Multiple Francisella tularensis subspecies and clades, tularemia outbreak, Utah.Emerg Infect Dis. 2008; 14: 1928-1930Crossref PubMed Scopus (31) Google Scholar, 5Siddle KJ Eromon P Barnes KG et al.Genomic analysis of Lassa virus during an increase in cases in Nigeria in 2018.N Engl J Med. 2018; 379: 1745-1753Crossref PubMed Scopus (83) Google Scholar This distinction is crucial for pneumonic plague because it speaks to the efficacy of control efforts. Pneumonic plague is not highly contagious, and it should be possible to interrupt person-to-person transmission through education campaigns and simple social distancing.6Kool JL Risk of person-to-person transmission of pneumonic plague.Clin Infect Dis. 2005; 40: 1166-1172Crossref PubMed Scopus (142) Google Scholar In this instance, control of person-to-person transmission could have been more effective than might be surmised from the overall epidemic curve. Molecular analysis of isolates from the outbreak should shed light on this possibility. Although the Madagascar outbreak was smaller than feared, the event was no less significant. In an already impoverished area, the cost and social disruption were considerable, and it is impossible to know what would have happened had the response been less robust. Nevertheless, it should be feasible to contain and control outbreaks of pneumonic plague with relative ease given our understanding of transmission and the availability of effective treatment. This outbreak underscores the need to develop and validate new diagnostics for use in resource-limited settings, to move toward less toxic and easier to administer treatments, and perhaps most importantly of all, to enhance public health messaging and communication. In the modern era, public fear and mistrust might be the greatest obstacles when combating plague outbreaks. Plague has a bad reputation, but the days of panic should be well in the past. I declare no competing interests. Epidemiological characteristics of an urban plague epidemic in Madagascar, August–November, 2017: an outbreak reportThis predominantly urban plague epidemic was characterised by a large number of notifications in two major urban areas and an unusually high proportion of pneumonic forms, with only 23% having one or more positive laboratory tests. Lessons about clinical and biological diagnosis, case definition, surveillance, and the logistical management of the response identified in this epidemic are crucial to improve the response to future plague outbreaks. Full-Text PDF Open Access