Quantifying the Transmission of Foot-and-Mouth Disease Virus in Cattle via a Contaminated Environment

FIG 1. Viral shedding from cattle infected with foot-and-mouth disease virus. Each plot shows the observed (open black circles) and predicted (posterior median [colored line] and 2.5th and 97.5th percentiles [shading]) level of shedding (log10 PFU/ml) in nasal and oral swabs from cattle used to contaminate the environment in four transmission experiments (rows). The route of challenge for each animal is indicated by color: needle-inoculated (red) and contact challenged (blue). The vertical dotted line indicates the time of clinical onset, if the animal displayed clinical signs.

FIG 2. Dynamics of foot-and-mouth disease virus (FMDV) in a contaminated environment. Each plot shows the observed and predicted level of virus (log10 PFU/ml) in different rooms (rows) (see Table 1) and environmental samples as follows: floor swabs (first column); wall swabs (second column); feed trough swabs (third column); and feces (fourth column). Observed levels are shown as black points, while predicted levels are shown as the posterior median (green line). For each room light gray shading indicates when FMDV-infected animals were present, medium gray shading indicates when the environmental challenge took place and transmission did not occur, and dark gray shading indicates when the environmental challenge took place and transmission occurred.

FIG 3. Dose-response relationship for environmental challenge with foot-and-mouth disease virus. The plot shows the posterior median (blue line) and 2.5th and 97.5th percentiles (blue shading). Black circles indicate the inferred mean level of contamination and the outcome (zero, unsuccessful; one, successful) for the 10 environmental challenges conducted in the present study.

FIG 4. Impact of decontamination on environmental transmission of foot-and-mouth disease virus. (A and B) Basic reproduction number (R0) (A) and probability of transmission (B) when decontamination is applied at 5 days postinfection (dpi) of the contaminating animal and reduces the viral titer in the environment by different amounts, as indicated in panel B by line color as follows: no reduction (red), 1 log10 (cyan), 2 log10 (magenta), 3 log10 (blue), or 4 log10 (black). (C and D) Basic reproduction number (R0) (C) and probability of transmission (D) when decontamination is applied at different dpi, as indicated in panel D by line color as follows: 2 dpi (red), 5 dpi (cyan), 10 dpi (magenta), 15 dpi (blue), or 20 dpi (black), and reduces the viral titer by 4 log10. Panels A and C show the posterior median (line) and 95% credible interval (shading), while panels B and D show the posterior median.

FIG 5. Comparison of predicted viral shedding (blue line) and environmental contamination (green line) for an individual bovine infected with foot-and-mouth disease virus. The figure shows the posterior median for the level of viral shedding, computed using equation 1 (see the Materials and Methods section), and the posterior median for the level of environmental contamination, computed using equation 2.

FIG 6. Schematic diagram showing the design of the environmental transmission experiments for foot-and-mouth disease virus in cattle. The days indicate approximate timings when the room was contaminated or when challenges took place in the room. C1 denotes needle-inoculated cattle, C2 denotes contact-challenged cattle, and C3 to C5 denote cattle challenged by exposure to an environment contaminated by two needle-inoculated animals (magnolia), two contact-challenged animals showing clinical signs (azure), or two contact-challenged animals prior to the onset of clinical signs (emerald). Donor cattle used to contaminate the room showing clinical signs of foot-and-mouth disease while in a room are shown in red.