Bravo-Vega, C. | bioRxiv Science

bioRxiv2021

Estimating real snakebite incidence in Colombia by using mathematical modelling and statistical inference.

Snakebite envenoming is a Neglected Tropical Disease affecting mainly deprived populations. Its burden is normally underestimated because patients prefer to seek for traditional medicine. Thus, applying strategies to optimize disease management and treatment delivery is difficult. We propose a framework to estimate snakebite incidence at a fine political scale based on available data, testing it in Colombia. First, we produced snakebite fine-scale risk maps based on the most medically important venomous snake species (Bothrops asper and B. atrox). We validated them with reported data in the country. Then, we proposed a generalized mixed effect model that estimates total incidence based on produced risk maps, poverty indexes, and an accessibility score that reflects the struggle to reach a medical center. Finally, we calibrated our model with national snakebite reported data from 2010 to 2019 using a Markov chain Monte Carlo (MCMC) algorithm and estimated underreporting based on the total incidence estimation. Our results suggest that 10.3% of total snakebite cases are not reported in Colombia and do not seek medical attention. The Orinoco and Amazonian regions (east of Colombia) share a high snakebite risk with a high underreporting. Our work highlights the importance of multidisciplinary approaches to face snakebite.

ecology↗

bioRxiv2021

Entangling snakebite dynamics: the spatiotemporal role of rainfall on snake envenoming in Colombia

The role of climate forcing on the population dynamics of infectious diseases has typically been addressed via retrospective analyses of aggregated incidence records over whole political regions. A central question in epidemiology has been whether seasonal and interannual cycles are driven by climate variation, or instead generated by other factors such as poverty or underreporting. Here, we use process-based models to determine the role of rainfall in the dynamics of snakebite, which is one of the main neglected tropical diseases around the world. We combined space-time datasets of snakebite incidence and rainfall for Colombia in combination with stochastic epidemiological models and iterated filtering methods to show the response to rainfall forcing, specifically, modulating the encounter frequency with venomous snakes. We identified six zones with different rainfall patterns to demonstrate that the relationship between rainfall and snakebite incidence was heterogeneous. Rainfall only drives snakebite incidence in regions with marked dry seasons, where rainfall becomes the limiting resource. In addition, the encounter frequency also differs between regions, and it is higher in regions where Bothrops atrox can be found. Our results show how the heterogeneous spatial distribution of snakebite risk seasonality in the country may be related to important traits of venomous snakes natural history. SIGNIFICANCE STATEMENTThe association between seasonal climatic variables and diseases epidemiology has helped to understand disease burden under changing environments. For example, for several tropical zoonotic diseases rainfall has been identified as a critical covariate inducing incidence seasonality. Snakebite envenoming is a disease that affects mostly economically deprived populations, and the availability of treatment is scarce. However, the role of environmental factors on snakebite is still missing in the literature. We formulated an epidemiological model to quantify the role of rainfall on snakebite seasonality throughout Colombia. We found that rainfall has a significant effect on incidence in places with a marked dry season (Caribbean and Orinoco plains), but in areas without dry season (Amazonian basin and southwestern Colombia) incidence exhibits no seasonality. This study is the first epidemiological modeling approach to snakebite and underscores the importance of rainfall as the limiting resource in this system. Thus, it is important to consider the interaction between climate forcing and venomous snakes ecology as determinants of envenomation risk.

ecology↗