Risk Assessment for the Transmission of Foot and Mouth Disease via Movement of Swine and Cattle Carcasses from FMD-infected Premises to a Disposal Site

Abstract

The present risk assessment proactively evaluated the risk of infecting susceptible livestock by the movement of Foot and Mouth Disease (FMD) infected carcasses (swine and cattle) from FMD infected premises. The risk assessment evaluated the most up to date available science and solicited opinion from experts when data was lacking. This risk assessment is proactive in nature and the scenarios, pathways and depopulation practices assessed were based on the current practices and regulations applicable during an animal disease outbreak in the US. The characteristics, types of conveyance methods, and equipment used to transport the infected carcasses were provided from expert opinion and verified through site visits. Different modeling techniques were used to estimate the number of infected animals during a FMD outbreak at various time intervals, the total time estimated from infection to depopulation and the total amount of FMD virus (FMDv) contained in a disposal truck. The main outcomes of the risk assessment should be reviewed if needed as new data becomes available in the future.

Risk estimation: The risk of FMD infection of susceptible livestock associated with the movement of swine and cattle carcasses from FMD infected premises to a disposal site during a FMD outbreak in the United States is negligible when using a standard rendering truck (tailgate sealed and tarp cover) and a Bio-Zip bag, and between negligible and low when using a standard rendering truck or a roll-off /dump truck with a Bio-Zip bag. The risk level in other scenarios (uncovered standard rendering trucks, uncovered roll-off/dump trucks, covered rolloff/ dump trucks and a liner) is between moderate and high.

Main results: Time for FMD detection was estimated by a disease spread model to be between 4-10 days for swine and beef cattle and 3-9 days for dairy cattle premises of different sizes. Total time from infection to depopulation (including detection and confirmation) for the first FMD infected case was estimated to be between 10-15 days for swine, 8-12 days for dairy and 10-14 days for beef cattle premises. Total time estimated for subsequent FMD cases was between 7-12 days for swine, 6-9 for dairy and 8-11 days for beef cattle premises. Most of the animals (>65% for the first case and >81% for subsequent cases) were viremic at the time of depopulation. The average concentration of FMDv in a carcass in experimental inoculation studies was 103 Plaque- Forming Unit per gram (PFU/g) for a pig carcass and 106 PFU/g for a cattle carcass. The total amount of infected carcasses moved to the disposal site (relative to the size of the animal carcass and the capacity of the truck trailer) was between 23-390 cattle carcasses and 117-780 pig carcasses per truck. Any small amount of body fluids (1 mL) would contain virus that is equal and greatly exceeds the infective dose by oral and inhalation route for pigs and cattle. The likelihood that swine and cattle carcasses moved from FMD positive premises will contain an infective dose was high. The use of a Bio-Zip bag in a standard rendering truck (tailgate sealed and tarp cover) reduces the likelihood of leakage, spillage and aerosolization to negligible.