CategorySwine Health-Foreign Animal Disease
Date Full Report Received02/05/2019
Date Abstract Report Received02/05/2019
Funded ByNational Pork Board
African swine fever virus or ASFV is a highly contagious foreign animal disease and a significant threat to pork production in the U.S. Disease caused by ASFV is characterized by severe disseminated hemorrhage and high mortality rates. Since spreading into Eastern Europe and Russia in 2007 and most recently into Belgium and China in 2018, the concern for further spread and introduction into negative countries such as the U.S. has heightened. With no effective treatment or vaccine available for ASFV control, preventing virus introduction is a primary goal of all virus-negative countries. Although the introduction of porcine epidemic diarrhea virus into the U.S. in April 2013 unveiled the risk of feed as a route for transboundary virus transmission, very little is known about the risks of other foreign animal diseases, such as ASFV, being transmitted through feed. The objectives of this project were to 1) define the relationship between infection probability and ASFV dose, 2) identify the minimum infectious dose (MID) or lowest dose required to result in ASFV infection of at least one pig, and 3) identify the median infectious dose (ID50) or dose required to result in ASFV infection of 50% of pigs for ASFV Georgia 2007 when consumed naturally in contaminated feed or liquid. To investigate these objectives, individually housed pigs were exposed to a single dose of ASFV ranging between 100 TCID50 and 108 TCID50 in small volumes of media (100 ml) or complete feed (100 g). Pigs were euthanized and assessed for ASFV infection by PCR and virus isolation at 5 days post-exposure. The MID of ASFV in liquid was 100 TCID50 whereas 104 TCID50 was the MID in complete feed. The ID50 was 101.0 TCID50 for liquid and 106.8 TCID50 for feed. Experimental data were statistically analyzed to model infection probability through multiple exposures, where the infection probability was shown to increase at all dose levels for both liquid and feed for exposures greater than 1. This is significant, as once a feed batch becomes contaminated with ASFV, it is likely that pigs would consume contaminated feed in higher volumes (>100 g) and at higher frequencies (>1 exposure) than what was tested in the current experiment. Overall, this work demonstrates that infection probability of ASFV through natural drinking and feeding behavior is dependent on dose, matrix, and number of exposures. Taken together, this study provides evidence that ASFV can be easily transmitted orally through contaminated liquid and feed when consumed naturally, with higher doses required for infection in complete feed, and provides additional information supporting the potential role of feed in ASFV transmission.