Who are the most affected by Bothrops snakebite envenoming in Brazil? A Clinical-epidemiological profile study among the regions of the country

Abstract

Snakebite envenoming represents an important Neglected Tropical Disease (NTD) that mainly affects tropical and subtropical developing countries according to the World Health Organization (WHO). As a priority issue in the tropics, it is estimated that accidental encounter between snakes and humans is the leading cause of morbidity and mortality among all NTDs in the world. In Brazil, an extremely diverse country with continental dimensions, snakebite envenoming is the second leading cause of reported human envenoming. Treating the disease has been an unprecedented challenge for Brazilian Health Systems for decades. Despite access to Antivenom therapy and distributing it free of charge across the country, Brazil faces numerous issues regarding the notification process and accurate treatment targeting for at-risk populations. Thus, this study aimed to identify the temporal epidemiological dynamics of accidents caused by Bothrops snakes in Brazil, the country's major group of venomous snakes, based on secondary information from the online database provided by The Brazilian Notifiable Diseases Information System (SINAN). For this purpose, reported Bothrops snakebites between 2012 and 2021 were counted, then the data were analyzed. We looked at the frequency, occurrence, mortality rates, case fatality rate (CFR), age and gender distribution, and the time lapse between the incident and the initiation of Antivenom therapy. The data were also organized considering regional variations of the country. Throughout the studied period, a total of 202,604 cases of envenoming caused by Bothrops spp. were notified, resulting in 766 fatalities. These accidents were found to occur in variable proportions across different regions in Brazil, with notable concentrations observed in the North, Northeast, and Southeast regions. The epidemiological profile of patients varied greatly between the regions, revealing that snake envenoming is much more a social, economic, and ecological problem than a medical one. In conclusion, our study provides an overview of the clinical and epidemiological profile of envenoming by Bothrops snakes in Brazil. Notably, this is the first study to present such information in a country as vast and diverse as Brazil, encompassing a comparative analysis of its regions using SINAN data, that proves to be a very useful national tool to improve the control and management of envenoming.

Fig 1. Occurrence and incidence of envenoming with Bothrops snakes in Brazil (2012–2021).

A) Map indicating the cumulative occurrence rates for the study period according to the state. B) Map indicating the cumulative occurrence rates for the study period according to region. C) Map showing the average incidence rates calculated by state (*envenoming/100,000 inhabitants). D) Map showing the average incidence rates calculated by region (*envenoming/100,000 inhabitants). The shapefiles for the municipalities, states and country, used for the creation of this map, were extracted from the Brazilian Institute of Geography and Statistics (https://www.ibge.gov.br/geociencias/todos-os-produtos-geociencias/15774-malhas.html).

Fig 2

A) Ranking of states with the highest occurrences associated with Bothrops spp. between 2012 and 2021. B) Trends in the annual occurrence of Bothrops envenoming according to the region of the country. The R² indicates how close the data are to the calculated linear regression line. C) Ranking of the 3 states with the highest incidence rates. The solid lines connecting the state names indicate that the state’s ranking position has been maintained from one year to the next, while the dashed lines indicate that the position has changed. Relative changes are shown according to annual incidence accompanied by green arrows indicating increase and red arrows indicating decrease.

Fig 3. General characteristics of the population affected by Bothrops envenoming between 2012 and 2021 in Brazil.

A) Ethnical characteristics of envenoming victims by region of the country. B) Population affected by envenoming according to gender (female or male). C) Age range of victims (groups: <1 year, between 1–4, 5–9, 10–14, 15–19, 20–39, 40–59, 60–64, 65–69, 70–79, 80 and >80 years).

Fig 4. Temporal itineraries of patients bite by Bothrops spp. graphically expressed by region from the moment of the bite until hospitalization (2012–2021).

The different colors of the fragments of each itinerary represent the time that the patients took from the moment of the bite until admission to the toxicological center that provided adequate Antivenom treatment.

Fig 5. Spatial distribution of reference health centers for handling Bothrops snakebites in Brazil, by incidence of envenoming per municipalities and regions.

The shapefiles for the municipalities, states and country, used for the creation of this map, were extracted from IBGE (https://www.ibge.gov.br/geociencias/todos-os-produtos-geociencias/15774-malhas.html). And the shapefile for the points representing the antivenom distribution were created by the authors using the addresses available at https://www.gov.br/saude/pt-br/assuntos/saude-de-a-a-z/a/animais-peconhentos/hospitais-de-referencia-para-atendimento.