Estimating snakebite incidence from mathematical models: A test in Costa Rica

Abstract

BackgroundSnakebite envenoming is a neglected public health challenge that affects mostly economically deprived communities who inhabit tropical regions. In these regions, snakebite incidence data is not always reliable, and access to health care is scare and heterogeneous. Thus, addressing the problem of snakebite effectively requires an understanding of how spatial heterogeneity in snakebite is associated with human demographics and snakes’ distribution. Here, we use a mathematical model to address the determinants of spatial heterogeneity in snakebite and we estimate snakebite incidence in a tropical country such as Costa Rica.Methods and findingsWe combined a mathematical model that follows the law of mass action, where the incidence is proportional to the exposed human population and the venomous snake population, with a spatiotemporal dataset of snakebite incidence (Data from year 1990 to 2007 for 193 districts) in Costa Rica. This country harbors one of the most dangerous venomous snakes, which is the Terciopelo (Bothrops asper, Garman, 1884). We estimated B. asper distribution using a maximum entropy algorithm, and its abundance was estimated based on field data. Then, the model was adjusted to the data using a lineal regression with the reported incidence. We found a significant positive correlation (R2 = 0.66, p-value < 0.01) between our estimation and the reported incidence, suggesting the model has a good performance in estimating snakebite incidence.ConclusionsOur model underscores the importance of the synergistic effect of exposed population size and snake abundance on snakebite incidence. By combining information from venomous snakes’ natural history with census data from rural populations, we were able to estimate snakebite incidence in Costa Rica. The model was able to fit the incidence data at fine administrative scale (district level), which is fundamental for the implementation and planning of management strategies oriented to reduce snakebite burden.

New insights into snakebite epidemiology in Costa Rica: A retrospective evaluation of medical records

“…Additionally, it is precisely at the beginning of the rainy seasons when the activities for agricultural production increase (land preparation, weeding, sowing; Boucher et al, 1983 ), which would suppose a greater exposure of people in the field. Recently, epidemiological compartmental models confirm that the incidence of snakebite depends on the relationship between the relative abundance of snakes and the human population ( Bravo-Vega et al, 2019 ), so it is highly likely that the peaks observed at the beginning of the rainy season resulted from such interaction.…”

“…This species adapts well to environments with a certain degree of human disturbance ( Sasa et al, 2009 ). Recent research has shown that the distribution and relative abundance of B. asper are good predictors of the overall incidence of snakebites in the country ( Bravo-Vega et al, 2019 ). Therefore, it is not surprising that prominent local tissue damage (edema, blisters, bleeding, and necrosis) and systemic effects (hemorrhage, coagulopathy, cardiovascular shock, and acute renal failure) in more severe cases are part of the repertoire of signs and symptoms that are generally manifested.…”

Novel transdisciplinary methodology for cross-sectional analysis of snakebite epidemiology at national scale

“…Recent studies have allowed to estimate human vulnerability to snakebite envenoming globally, by using proxy data on risk factors such as healthcare gaps, unavailability of antivenoms, and presence of medically important snake species [ 15 ], or through mathematical models [ 16 ], but without a direct measure of snakebite incidence and mortality. Additionally, new digital health applications have shown that it is partially possible to estimate areas of high snakebite incidence and identify populations at risk through citizen science [ 15 , 17 , 18 ] in countries where social media, citizen forums, and scientific online platforms are used to report snake-human encounters and map their geographic distributions [ 17 , 19 ].…”

Implications of global environmental change for the burden of snakebite

“…To illustrate land use change effects on snakes, we modeled the influence of land cover change on suitable habitat for the terciopelo ( Bothrops asper ), the most significant venomous snake in Central America ( Bravo-Vega et al, 2019 ), during the period 2003–2004 to 2011–2013 in Central America. We used monthly MODIS (Moderate Resolution Imaging Spectroradiometer; https://modis.gsfc.nasa.gov/ ) data to characterize, through the NDVI (Normalized Difference Vegetation Index), the greenness of each pixel, and assess potential changes in vegetation cover.…”