Abstract
The introduction and spread of porcine epidemic diarrhoea virus (PEDV) in North America resulted in significant death loss in the swine industry. As the industry learned how to manage this disease, many new risks were identified, including the potential for feed and feed ingredients to become contaminated and spread PEDV. In addition, biosecurity practices were reevaluated and strengthened throughout the industry. At the time of the outbreak epidemiologists did not understand, as well as they are understood today, all the risk factors that contribute to the spread of PEDV. As a result, the epidemiological investigations into the 2014 PEDV outbreak in eastern Canada may not have investigated all risk factors as thoroughly as they would be investigated today. In retrospect, many of the Bradford Hill criteria used to determine causation were not fulfilled. This review identifies risk factors that were not included in the 2014 epidemiology. If these risk factors were included in the epidemiology, the conclusions and determination of causation may have been different.
Highlights
Epidemiological investigations typically examine associations between exposure variables and health outcome
Cleaned trucks returning to Canada after delivering pigs to US abattoirs was not considered as a source of porcine epidemic diarrhoea virus (PEDV) introduction in eastern Canada
The possibility that imported non-animal feed ingredients contaminated with PEDV, such as soybean meal, could have introduced PEDV into eastern Canada was not investigated
Summary
Epidemiological investigations typically examine associations between exposure variables and health outcome. Contaminated non-animal feed ingredients infecting market hogs could be an alternative explanation of a potential source of the PEDV-positive environmental samples at the Quebec abattoir and the Ontario assembly yard (Bedard, 2014; Mann, 2014). It is unfortunate that the Canadian epidemiology did not investigate contact between the assembly yard, farms included in the initial PEDV outbreak, the feed plant that manufactured the nursery feed for the Index cases and other high traffic sites.
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