Model-based analysis of an outbreak of bubonic plague in Cairo in 1801

Abstract

Bubonic plague has caused three deadly pandemics in human history: from the mid-sixth to mid-eighth century, from the mid-fourteenth to the mid-eighteenth century and from the end of the nineteenth until the mid-twentieth century. Between the second and the third pandemics, plague was causing sporadic outbreaks in only a few countries in the Middle East, including Egypt. Little is known about this historical phase of plague, even though it represents the temporal, geographical and phylogenetic transition between the second and third pandemics. Here we analysed in detail an outbreak of plague that took place in Cairo in 1801, and for which epidemiological data are uniquely available thanks to the presence of medical officers accompanying the Napoleonic expedition into Egypt at that time. We propose a new stochastic model describing how bubonic plague outbreaks unfold in both rat and human populations, and perform Bayesian inference under this model using a particle Markov chain Monte Carlo. Rat carcasses were estimated to be infectious for approximately 4 days after death, which is in good agreement with local observations on the survival of infectious rat fleas. The estimated transmission rate between rats implies a basic reproduction number R0 of approximately 3, causing the collapse of the rat population in approximately 100 days. Simultaneously, the force of infection exerted by each infected rat carcass onto the human population increases progressively by more than an order of magnitude. We also considered human-to-human transmission via pneumonic plague or human specific vectors, but found this route to account for only a small fraction of cases and to be significantly below the threshold required to sustain an outbreak.

Human ectoparasites and the spread of plague in Europe during the Second Pandemic

“…The strength of our study is that we compared three plague transmission models, each representing a known or hypothetical mode of plague transmission, for nine plague outbreaks across the spatial and temporal extent of the Second Pandemic in Europe. Our study thus provides a more general understanding of plague epidemics in Europe than previous modeling studies that focus on single outbreaks, or single transmission routes ( 11 , 20 , 35 , 36 , 51 ). However, since we considered nine outbreaks over several centuries, we were limited to using simple models that could be applied systematically.…”

Plague Transmission from Corpses and Carcasses

“…Kool (42) summarized data from historical records and contemporary experiences and used qualitative analysis to conclude that "pneumonic plague is not easily transmitted from one person to another." Some analysts have estimated transmission potential of plague using mathematical models based on historical data (43,44). The studies in this review, which examine mostly modern plague outbreaks (many earlier reports did not provide sufficient detail to meet our inclusion criteria), provide evidence that pneumonic plague is transmissible from human to human, but only after close and prolonged exposure.…”

“…; Appendix Tables 27,29,31,33,35,37,39,41,43,45, 47, 49, 51, 53, 55, 57). Twelve studies did not describe efforts to trace all contacts of the index patient.…”

Risk of plague transmission from human cadavers: a systematic review

“…Indeed, a systematic review summarized data from historical records and contemporary experience, and based on qualitative analysis concluded that “pneumonic plague is not easily transmitted from one person to another” [41]. Quantitative assessment of transmissibility of plague has also been performed, using mathematical models based on historical data [42,43]. Our data, which include most recent outbreaks (older reports usually do not provide enough information to allow inclusion in the review) support that pneumonic plague is transmissible from human to human, sometimes only after close and prolonged exposure.…”