Passover and Plague

PASSOVER AND PLAGUE MARTIN J. BLASER* The development of agriculture, and the consequent storage of food, was a major advance in human history [I]. Yet the transformation from hunter-gatherer and pastoral antecedents to a farming society with fixed settlements had important consequences for disease transmission [2, 3]. In particular, the storage of food amplified the exposure of humans to food-eating pests and to their parasites [4] . The paradigm for this phenomenon is bubonic plague, transmitted by the fleas of rodents, and caused by the gram-negative bacterium, Yersinia pestis [5]. This paper suggests that observance of the laws relating to theJewish festival of Passover diminishes risk to the individual and to the community for the transmission of plague. The hypothesis raised is that an important consequence of the annual observance of the religious requirements for Passover is that there is an essentially complete removal of grain and food wastes from the household prior to the expected seasonal peak for plague, a process that curtails or minimizes local rodent populations. As a result, aJewish community would be expected to be at diminished risk for epidemic plague. Etiology and Transmission ofPlague Human plague is a vector-borne zoonosis (4-7) . Y. pestis chiefly infects rodents, causing enzootic and epizootic disease, and is transmitted by any one of several species of fleas. In general, these vectors prefer to parasitize rodents, but they mayjump to new mammalian hosts, especially when their host populations die. Arboreal rodent populations in many parts of the The author thanks Rabbis Jeffrey M. Cohen, David Lieber, Ronald Roth, and Peter Haas, and Drs. Stephen R. Ell, Ward Bullock, and F. Marc LaForce, for uieir scholarly advice, and M. Janelle Gervickas for secretarial support. The author dedicates this work to his father, Frederick S. Blaser, on the occasion of his 80th birthday. *Department of Medicine, Vanderbilt University School of Medicine, and VA Medical Center , Nashville, TN. Correspondence: Vanderbilt University School of Medicine, A-3310 Medical Center North, Nashville, TN 37232.© 1998 by the University of Chicago. All rights reserved. 0031-5982/98/4102-1054$01.00 Perspectives in Biology and Medicine, 41, 2 ¦ Winter 1998 | 243 world carry Y. pestis. In rural areas, sporadic cases of human plague are usually derived from enzootic plague among the local rodent species; this is termed sylvatic plague [8, 9]. On occasion, there is transmission of Y. pestis from sylvatic rodents to indigenous rodent populations associated with concentrations of human settlement; this mav result in urban plague. In general, human plague is a problem of urban communities. Without gross aggregations of population, there can be no major epidemics, and without commerce between towns, these cannot spread [7] . Rodents are the principal, if not exclusive, reservoir for human plague. Rats are attracted to human settlements by their food stores and food wastes. In particular , urban bubonic plague is a rat disease; without rats, there is no urban plague [7] . Both endemic and epidemic plague have peak activity following increases in rodent and flea populations and in plague among rodents, which in temperate climates is in the summer [6, 7, 10-13]. Shifts in predominant rat species and their proximity to humans may be responsible for changes in the epidemiology of plague [7, 14]. Rat-infested human settlements are prime targets for the eruption of urban plague after the introduction of Y. pestis into the rodent population. Human infection may then lead to human-to-human transmission, either as a result of spread from airborne droplets from persons with pneumonic plague or pharyngeal carriers or via infected fleas [5, 15-17]. Once conditions are sufficient for the introduction of flea-borne plague into a community, controlling subsequent flea-to-human and human-to-human transmission is difficult if not impossible [16, 17]. Thus, programs to prevent outbreaks of plague must first be based on control of urban rat populations. Plague in Antiquity In China and India, plague has long been associated with rodents [7]. The ancient Hindu Bhagavata Acrawawarned villagers to desert their dwellings as soon as dead rats were seen, for death among rats was the harbinger of the death of humans [18]. To the ancient Greeks, Apollo Smintheus, the god who protected...