Vulnerability to snakebite envenoming: a global mapping of hotspots

Abstract

Background: Snakebite envenoming is a frequently overlooked cause of mortality and morbidity. Data for snake ecology and existing snakebite interventions are scarce, limiting accurate burden estimation initiatives. Low global awareness stunts new interventions, adequate health resources, and available health care. Therefore, we aimed to synthesise currently available data to identify the most vulnerable populations at risk of snakebite, and where additional data to manage this global problem are needed.

Methods: We assembled a list of snake species using WHO guidelines. Where relevant, we obtained expert opinion range (EOR) maps from WHO or the Clinical Toxinology Resources. We also obtained occurrence data for each snake species from a variety of websites, such as VertNet and iNaturalist, using the spocc R package (version 0.7.0). We removed duplicate occurrence data and categorised snakes into three groups: group A (no available EOR map or species occurrence records), group B (EOR map but <5 species occurrence records), and group C (EOR map and ≥5 species occurrence records). For group C species, we did a multivariate environmental similarity analysis using the 2008 WHO EOR maps and newly available evidence. Using these data and the EOR maps, we produced contemporary range maps for medically important venomous snake species at a 5 × 5 km resolution. We subsequently triangulated these data with three health system metrics (antivenom availability, accessibility to urban centres, and the Healthcare Access and Quality [HAQ] Index) to identify the populations most vulnerable to snakebite morbidity and mortality.

Findings: We provide a map showing the ranges of 278 snake species globally. Although about 6·85 billion people worldwide live within range of areas inhabited by snakes, about 146·70 million live within remote areas lacking quality health-care provisioning. Comparing opposite ends of the HAQ Index, 272·91 million individuals (65·25%) of the population within the lowest decile are at risk of exposure to any snake for which no effective therapy exists compared with 519·46 million individuals (27·79%) within the highest HAQ Index decile, showing a disproportionate coverage in reported antivenom availability. Antivenoms were available for 119 (43%) of 278 snake species evaluated by WHO, while globally 750·19 million (10·95%) of those living within snake ranges live more than 1 h from population centres. In total, we identify about 92·66 million people living within these vulnerable geographies, including many sub-Saharan countries, Indonesia, and other parts of southeast Asia.

Interpretation: Identifying exact populations vulnerable to the most severe outcomes of snakebite envenoming at a subnational level is important for prioritising new data collection and collation, reinforcing envenoming treatment, existing health-care systems, and deploying currently available and future interventions. These maps can guide future research efforts on snakebite envenoming from both ecological and public health perspectives and better target future estimates of the burden of this neglected tropical disease.

Funding: Bill & Melinda Gates Foundation.

Figure 1

Conceptual overview of vulnerability to snakebite envenoming (A) Vulnerability can be considered as the intersection of populations who live within the range of venomous snakes that have no antivenoms available, cannot easily access health care, and have poor quality health care in delivery of antivenoms or ensuring necessary stocks. The intersection of all three defines the most vulnerable populations. (B) These factors vary in space. By overlaying these features, the most vulnerable populations can be identified spatially (represented here by the boxes outlined in black).

Figure 2

Ranges of venomous snake species and number of medically important venomous snake species per 5 × 5 km location for which no effective therapy is currently listed by WHO (A) Counts range from low (n=1) to high (n=13). The light grey areas represent locations where no medically important venomous snake species are present. (B) Counts range from low (n=1) to high (n=7). The light grey areas represent locations where snake species present have effective therapies listed by WHO, and the dark grey areas represent locations where no medically important venomous snake species are present.

Figure 3

Average travel time to nearest major city for populations living within snake ranges The light grey areas represent locations without the presence of medically important venomous snake species.

Figure 4

Proportion of populations living within range of snake species by each HAQ Index decile (A) Populations living within the range of one or more medically important venomous snake species (either category one or two). (B) Populations living within the range of one or more medically important venomous snake species (either category one or two), for which no effective therapy is listed. HAQ=Healthcare Access and Quality.

Figure 5

Hotspots of vulnerable populations to medically important venomous snake species Hotspots are defined as people living in areas within the range of one or more medically important venomous snake species, and more than 3 h away from major urban centres with Healthcare Access and Quality Index deciles of 1–3. (A) Pixel-level vulnerability surface (ie, vulnerability to all species of medically important snakes). (B) Aggregated second administrative level vulnerability to all species of medically important venomous snakes, as measured by the absolute number of people. (C) Aggregated second administrative level vulnerability to only those species for which no effective therapy is currently listed by WHO, as measured by the absolute number of people.