The Great Epizootic of 1872-73

Illustration from dissection of horse that succumbed to 1872-73 epizootic.

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Map of the Great Epizootic of 1872-73. Each point on the map documents when the disease was first reported to have arrived in that city, based on firsthand observations of infected horses.

In 1872-73, horses in Toronto infected nearly all urban horses in Canada and the US with an unknown disease (likely equine influenza). This map shows that extraordinary story.

Above is an animated map of the Great Epizootic of 1872-73, showing its arrival in 164 Canadian and US cities and towns between September 29, 1872 and September 28, 1873. If you click the “play” button at the bottom of the map, you can watch the spread of this disease that infected urban horses across Canada and the US during this period, incapacitating the animals and preventing them from working. You can also click on each infected city to see the sources used to determine what date the disease arrived.

I built this map using more than 480 newspaper articles, veterinary reports, and other contemporary accounts of the epizootic. These historical documents allowed me to approximate the arrival of the disease in each city to within a couple of days and then plot that information in a Geographic Information System database in ArcGIS. Using the Time Aware tool from ArcGIS Online, I was then able to animate this historical geographic information and observe how the epizootic spread throughout the continent. This work was inspired by the excellent book, Historical GIS Research in Canada.

The results proved quite interesting and I would encourage readers to take a look at a new article that I published based on this HGIS project. You can find it in Environmental History (July 2018) right here. It outlines the main findings from the map, highlighting relationships among humans, horses, railroads, and urban environments. In this article, I argue that the Great Epizootic provides evidence that networked urbanization produced forms of historical biotic homogenization that could result in the rapid and widespread outbreak of animal disease. I blend urban environmental history, animal history, histories of health and disease, and history of science to better understand this remarkable event.

The research for this article is part of my ongoing project on the history of urban animals in Canada. Readers can find out more about this project on my research page here:

This page includes all my blog articles on this subject on The Otter, all my publications, and some open data from my research, including the map files for the animated map in this post.

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Sean Kheraj

Associate Professor and Vice-Provost Academic at Toronto Metropolitan University
Sean Kheraj is a member of the executive committee of the Network in Canadian History and Environment. He's an associate professor in the Department of History and Vice-Provost Academic at Toronto Metropolitan University. His research and teaching focuses on environmental and Canadian history. He is also the host and producer of Nature's Past, NiCHE's audio podcast series and he blogs at

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