HISTORICAL REVIEW agent hosted in a rain-sensitive rodent reservoir was responsi- ble for the disease. Many of the symptoms described by Dr. Hernandez occur to a degree in infections by rodent-borne South American arenaviruses, but no arenavirus has been pos- itively identified in Mexico. Hantavirus is a less likely candi- date for cocoliztli because epidemics of severe hantavirus hemorrhagic fevers with high death rates are unknown in the New World. The hypothesized viral agent responsible for cocoloztli remains to be identified, but several new arenavi- ruses and hantaviruses have recently been isolated from the Americas and perhaps more remain to be discovered (11). If not extinct, the microorganism that caused cocoliztli may remain hidden in the highlands of Mexico and under favorable climatic conditions could reappear. Acknowledgments This research was funded by the National Science Foundation, Paleoclimatology Program Grant number ATM 9986074. Dr. Acuna-Soto is a professor of epidemiology on the Faculty of Medicine at Universidad Nacional Autonoma de Mexico. He is par- ticularly interested in the history and environmental context of dis- ease in Mexico. References 1. Cook SF, Simpson LB. The Population of Central Mexico in the Six- teenth Century. Ibero Americana Vol. 31, Berkeley: University of Califor- nia Press; 1948. 2. Gerhard P. A guide to the historical geography of New Spain. Norman, OK: University of Oklahoma Press; 1993. 3. Hugh T. Conquest, Montezuma, Cortez, and the Fall of Old Mexico. New York: Simon and Schuster; 1993. 4. Acuna-Soto R, Caderon Romero L, Maguire JH. Large epidemics of hem- orrhagic fevers in Mexico 1545-1815. Am J Trop Med Hyg 2000; 62:733-9 5. Marr JS, Kiracofe JB. Was the Huey Cocoliztli a haemorrhagic fever? Med Hist, 2000;44:341-62. 6. Stahle DW, Cleaveland MK, Therrell MD, Villanueva-Diaz J. Tree-ring reconstruction of winter and summer precipitation in Durango, Mexico, for the past 600 years. 10th Symposium Global Change Studies. Boston: American Meteorological Society, 1999; 317-8. 7. Stahle DW, Cook ER, Cleaveland MK, Therrell MD, Meko DM, Gris- sino-Mayer HD, et al. Tree-ring data document 16th century megadrought over North America. Eos 2000;81:121-5. 8. Schmaljohn C, Hjelle B. Hantaviruses: a global disease problem. Emerg Infect Dis 1997;3:95-104. 9. Hjelle B. Glass GE. Outbreak of hantavirus infection in the Four Corners region of the United States in the wake of the 1997-1998 El Nino-South- ern Oscillation. J Infect Dis 2000;181:1569-73. 10. Malvido E. Cronologia de las epidemias y crisis agricolas de la epoca colonial. Historia Mexicana 1973;89:96-101. 11. Peters CJ. Hemorrhagic fevers: How they wax and wane. In: Scheld WM, Armstong D, Hughes JM, editors. Emerging infections. Washington DC: American Society for Microbiology, 1998;15-25. Address for correspondence: David Stahle, Tree-Ring Laboratory, Department of Geosciences, Ozark Hall 113, University of Arkansas, Fayetteville, AR 72701 USA; fax: 479-575-3846; e-mail address: dstahle@mail.uark.edu 362 Emerging Infectious Diseases • Vol. 8, No. 4, April 2002