Duration of Contagion of FMDV in Infected Live Pigs and Carcasses

Authors: STENFELDT, CAROLINA - University Of Kansas; BERTRAM, MIRANDA - Oak Ridge Institute For Science And Education (ORISE); Smoliga, George; Hartwig, Ethan; DELGADO, AMY - Animal And Plant Health Inspection Service (APHIS); Arzt, Jonathan

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2020
Publication Date: 6/11/2020
Citation: Stenfeldt, C., Bertram, M., Smoliga, G.R., Hartwig, E.J., Delgado, A., Arzt, J. 2020. Duration of Contagion of FMDV in Infected Live Pigs and Carcasses. Frontiers in Veterinary Science. https://doi.org/10.3389/fvets.2020.00334.
DOI: https://doi.org/10.3389/fvets.2020.00334

Interpretive Summary: Computer models can be used to estimate how disease outbreaks would spread within a population. However, such models are dependent on input data that describes how and when a specific disease can spread between infected animals. The current investigation describes a study that was performed to determine for how long after infection pigs were able to spread foot-and-mouth disease virus (FMDV) to other pigs. To answer this question, one group of pigs that had been infected with FMDV were put into contact with separate groups of pigs at 5, 10, and 15 days after they had been infected. The groups of pigs that had been in contact with the "donor pigs" at 5 and 10 days after infection became sick, but the 15 day contact group did not get sick. Virus in samples of muscle was inactivated within few days after the death of FMDV infected pigs. However, virus in FMD lesions remained active until the study ended at 11 weeks after the death of the pigs. The results from this study can be used to model the risk associated with FMDV-infected pigs and carcasses. These findings help to protect USA livestock herds from transboundary diseases like FMD.

Technical Abstract: Data-driven modeling of high-consequence pathogen incursions is a critical component of veterinary preparedness. However, simplifying assumptions and excessive use of proxy values to compensate for gaps in available data may compromise modeled outcomes. The current investigation was specifically designed to address two major gaps in current knowledge of foot-and-mouth disease virus (FMDV) pathogenesis in pigs: the end (duration) of the infectious period and the viability of FMDV in decaying carcasses. By serial exposure of sentinel groups of pigs to the same group of donor pigs, it was demonstrated that infected pigs transmitted disease at 10 days post infection (dpi), but not at 15 dpi. Assuming a latent period of 1 day, this would result in a conservative estimate of an infectious duration of 9 days, which is considerably longer than suggested by a previous report from an experiment performed in cattle. Airborne contagion was diminished within two days of removal of infected pigs from isolation rooms. Similarly, FMDV in muscle was inactivated within 7 days in carcasses stored at 4oC. By contrast, FMDV infectivity in vesicle epithelium harvested from intact carcasses stored under similar conditions remained remarkably high until the study termination at 11 weeks post mortem. The output from this study consists of experimentally determined data on contagion associated with FMDV-infected pigs. This information should be considered for parameterization of models used for foot-and-mouth disease outbreak simulations involving areas of substantial pig production.