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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 h (95%CI 21, 29), incubation: 70 h (95%CI 64, 76), pre-clinical infectious: 36 h (95%CI 32, 41), clinical infectious: 265 h (95%CI 258, 272) and total infectious: 282 h (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., (Published by Elsevier B.V.)

The current investigation applied a Bayesian modeling approach to a unique experimental transmission study to estimate the occurrence of transmission of foot-and-mouth disease (FMD) during the incubation phase amongst group-housed pigs. The primary outcome was that transmission occurred approximately one day prior to development of visible signs of disease (posterior median 21 hours, 95% CI: 1.1-45.0). Updated disease state durations were incorporated into a simulation model to examine the importance of addressing preclinical transmission in the face of robust response measures. Simulation of FMD outbreaks in the US pig production sector demonstrated that including a preclinical infectious period of one day would result in a 40% increase in the median number of farms affected (166 additional farms and 664,912 pigs euthanized) compared to the scenario of no preclinical transmission, assuming suboptimal outbreak response. These findings emphasize the importance of considering transmission of FMD during the incubation phase in modeling and response planning.

Foot-and-mouth disease (FMD) is an important transboundary disease with substantial economic impacts. Although between-herd transmission of the disease has been well studied, studies focusing on within-herd transmission using farm-level outbreak data are rare. The aim of this study was to estimate parameters associated with within-herd transmission, host physiological factors and FMD virus (FMDV) persistence using data collected from an outbreak that occurred at a large, organized dairy farm in India. Of 1,836 regularly vaccinated, adult dairy cattle, 222 had clinical signs of FMD over a 39-day period. Assuming homogenous mixing, a frequency-dependent compartmental model of disease transmission was built. The transmission coefficient and basic reproductive number were estimated to be between 16.2-18.4 and 67-88, respectively. Non-pregnant animals were more likely to manifest clinical signs of FMD as compared to pregnant cattle. Based on oropharyngeal fluid (probang) sampling and FMDV-specific RT-PCR, four of 36 longitudinally sampled animals (14%) were persistently infected carriers 10.5 months post-outbreak. There was no statistical difference between subclinical and clinically infected animals in the duration of the carrier state. However, prevalence of NSP-ELISA antibodies differed significantly between subclinical and clinically infected animals 12 months after the outbreak with 83% seroprevalence amongst clinically infected cattle compared to 69% of subclinical animals. This study further elucidates within-herd FMD transmission dynamics during the acute-phase and characterizes duration of FMDV persistence and seroprevalence of FMD under natural conditions in an endemic setting., (© 2017 Blackwell Verlag GmbH.)