Preliminary parameter values for the SIR model.

Spatial range of transhumant cattle movements in The Gambia identified from the household survey.

Movements originated from study villages (represented as red squares) and extended to destination villages, which are either other study villages or villages not selected for this study (represented as black triangles). This study was conducted during the dry season, and all transhumant herds were sampled at their destination villages. Distinct directional movements between homestead villages and their respective destinations are illustrated with blue arrows. The Gambia river is depicted as the meandering white line running the length of the country. The map was generated using the igraph package in R.

Epidemiological model of RVFV transmission and infection dynamics among the cattle subpopulations in The Gambia.

A. Schematic representation of ecoclimatic region and seasonal combinations that influences RVFV transmission between the Sahelian areas and the Gambia river eco-region. B. The transmission matrices that determined possible RVFV transmissions between the subpopulations during each season. C. Transmission framework of the within eco-region RVFV transmission, parameters are defined within the main text.

Distribution of degree, normalised betweenness and eigenvector centrality values based on cross-sectional household survey data on livestock movement.

Only a few of households showed high centrality values, highlighting their importance in the network.

Time-series of the proportion of infectious cattle in the three subpopulations across the two eco-regions.

Main: The simulated RVF infection dynamics from the deterministic model (solid lines) together with twenty realisations of the stochastic model (dashed lines). Insert: A magnified view highlighting the seasonal dynamics of RVFV transmission focused on the last two years of the 20-year deterministic simulation in the cattle subpopulations, highlighting finer seasonal variations (wet season = beige; dry season = cyan). The proportion of infectious cattle peaked at the latter part of the wet season, but infections quickly disappeared in the dry season in the Sahelian eco-region. Once transhumant herds begin to arrive in the Gambia river region, infections are predicted to rise. I = infectious cattle in each subpopulation. A square root transformation was applied to the y-axis for visualisation purposes using coord_trans(y = "sqrt"), while the data remained in its original scale.

Mean posterior values and 95% CrI of the estimated parameters.

Extinction rate of RVFV over time (red line with 95% CI – grey ribbon), in the transhumant subpopulation (A) and the entire cattle population within the system (B) based on 1,000 stochastic realisations, illustrating differences in the timing of local and system-wide extinctions, respectively.

Most of the local extinction occurred shortly after RVFV introduction into a fully susceptible population in the T subpopulation. Note: the timing of the local extinction in the T subpopulation depicted here was the first extinction event within this subpopulation, and re-infection occurs whence the subpopulation returned to the river.

The full 10-year simulation of the weekly 𝑅𝑠𝑑 (green), and force of infection, πœ†π‘Ÿπ‘’π‘”π‘–π‘œπ‘›,π‘ π‘’π‘Žπ‘ π‘œπ‘›, in each eco-region (blue = Sahelian, red = Gambia river eco-region).

Shaded areas correspond to the seasons (wet season = beige; dry season = cyan) in the last two years of the simulation. A square root transformation was applied to the y-axis for visualization purposes.

Summary of estimated seasonal reproduction number (𝑅𝑠𝑑) and regio-specific force of infection (πœ†π‘–)

Predicted RVFV seroprevalence in each population subject to FOI during the wet and dry seasons.

A: Cumulative growth of RVFV immunity over a 10-year period, representing the hypothetical lifespan of cattle, with no consideration for decay of RVFV seropositivity (πœ‹ = 0). B: Proportion of immune cattle after introducing a seropositivity decay parameter (πœ‹ = 0.0035), aligning the predicted seroprevalence with observed data. Observed seroprevalence across different age classes in the three structured cattle populations in The Gambia is shown as dots, with 95% confidence intervals (CI) as error bars. P: Cattle exposed to RVFV infection and recovered, assumed to be seropositive.

Simulated RVF infection dynamic over a 20-year period within each structured cattle subpopulation, assuming a ban on seasonal transhumant movement.

In the Sahelian eco-region, periodic large outbreaks were separated by long inter-epidemic periods, allowing the susceptible subpopulations to regrow. In contrast, RVFV infection remained sustained and low in amplitude in the Gambia river eco-region – comparable to when movement was allowed. I = infectious cattle in each subpopulation. A square root transformation was applied to the y-axis for visualization purposes.

The elasticity for all eight parameters in the GLM.

The parameters with the largest coefficient are in shown in bold.