Parameterization of the durations of phases of foot-and-mouth disease in pigs

Authors: MORENO-TORRES, KARLA - Animal And Plant Health Inspection Service (APHIS); DELGADO, AMY - Animal And Plant Health Inspection Service (APHIS); BRANAN, MATTHEW - Animal And Plant Health Inspection Service (APHIS); YADAV, SHANKAR - Animal And Plant Health Inspection Service (APHIS); STENFELDT, CAROLINA - University Of Kansas; Arzt, Jonathan

Submitted to: Preventive Veterinary Medicine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2022
Publication Date: 3/18/2022
Citation: Moreno-Torres, K., Delgado, A.H., Branan, M.A., Yadav, S., Stenfeldt, C., Arzt, J. 2022. Parameterization of the durations of phases of foot-and-mouth disease in pigs. Preventive Veterinary Medicine. https://doi.org/10.1016/j.prevetmed.2022.105615.
DOI: https://doi.org/10.1016/j.prevetmed.2022.105615

Interpretive Summary: Foot-and-mouth disease (FMD) is a viral infection of livestock of critical socioeconomic importance. It is well-known that pigs are highly susceptible to FMD and if there were an outbreak in the USA it would have major impact to the pig production industries. However, the mathematical models that are required to predict FMD spread amongst pigs are outdated. The current study utilized laboratory findings generated within the Foreign Animal Disease Research Unit (FADRU) to standardize the use of data to model FMD in pigs. Important findings include the determinations that pigs are infectious for over 11 days and that they have an incubation period of almost 3 days. This information is important to US agriculture because precise modeling of FMD in pigs is a critical aspect of FMD control in the event of an outbreak in the USA.

Technical Abstract: The global interconnectedness of the pig-production industry and the diversity of foot-and-mouth disease (FMD) viruses (FMDVs) currently circulating, makes modeling disease spread and control in FMD-free areas challenging. However, advances in experimental design and transmission studies create opportunities to strengthen our understanding and ability to model FMD transmission. In the current study, we estimated the duration of defined phases of FMDV infection in pigs by using data from a large collection of controlled in vivo experiments. Because the detection of low-levels of viral RNA does not correspond to infectiousness, an experimentally defined minimum threshold of FMDV RNA shedding in oropharyngeal fluids was used to estimate the onset of infectiousness in experiments in which transmission was not evaluated. Animal-level data were used in Accelerated Failure Time models to assess the effect of experimental design factors in the duration of defined phases of FMDV infection: latent, incubation, pre-clinical infectious, clinical infectious, and total infectious periods. The estimated means of the phases were latent: 25 hours (95%CI 21, 29), incubation: 70 hours (95%CI 64, 76), pre-clinical infectious: 36 hours (95%CI 32, 41), clinical infectious: 265 hours (95%CI 258, 272) and total infectious: 282 hours (95%CI 273, 290). Virus strains and exposure methods had no significant influence on the duration of latency, incubation, or clinical infectious phases. By contrast, the estimated means of the duration of the pre-clinical infectious and total infectious phases were significantly influenced by virus strains, and the duration of the pre-clinical infectious phase was significantly influenced by exposure methods. This study provides disease parameters based on an estimated threshold of the onset of infectiousness and a probability distribution representing the end of infectiousness. Disease parameters that incorporate experimentally-based quantitative proxies to define phases of FMDV infection may improve planning and preparedness for FMD.