What makes a snake bite? A South Africa perspective

Abstract

Increasing interactions between humans and snakes have raised the profile of human-snake conflict as a primary contributor to the public health challenge of snakebite. In 2017, the World Health Organisation declared snakebite as a neglected tropical disease as human snakebite incidences were reported to reach over 5 million per year globally, with between 81 000 and 138 000 deaths. The tropics have the highest prevalence of snakebite incidences as they have a high diversity of venomous snake species and the presence of more vulnerable human populations. Temperate regions such as South Africa also have a high diversity of snake fauna and although the number of venomous snake species does not outweigh the number of non-venomous snake species, snakebite incidences are reported to occur frequently. My research aimed to increase the knowledge of the driving factors of snakebite incidences in South Africa and investigate the behavioural ecology of some of the medically important snake species responsible for these incidences. Snakebite appears to be generally well managed in South Africa and assessed datasets show that there are few recorded deaths. This is partly due to the fact that the current healthcare index is ranked highest in Africa. However, snakebite incidences are relatively high and underreported. The available datasets show a prevalence of 5.63 per 100 000 individuals, but this is likely higher due to lack of reporting from the majority of healthcare facilities. As predicted, most incidences take place during warmer months (November – March) in the evening, with males under the age of 30 accounting for the majority of these incidences. Key information regarding the circumstances of incidences is not reported but based on available information, most incidences take place when people are walking and interacting with a snake, as indicated by the large number of bites on hands. Snakebite incidences are also distributed widely across the country, but hotspots occur in areas of high population density such as Johannesburg, Durban and Cape Town, with the vast majority taking place outside of protected areas. The higher numbers of incidences in human populated areas indicate that interactions between people and snakes occur frequently. During these interactions, different snake species exhibit a range of defensive behaviours. As interactions between humans and snakes increase, gaining insight into the factors that influence these behaviours is crucial. Behavioural experiments on puff adder (Bitis arietans), black mamba (Dendroaspis polylepis) and snouted cobra (Naja annulifera) showed that snakes are most likely to strike and bite when a threat is in very close proximity (< 50 cm) and although generally quite tolerant of harassment, bites are likely if they are repeatedly provoked. Even D. polylepis with its long body length will flee rather than strike when provided the opportunity. However, strike velocities were high for all three species (< 0.4 seconds) indicating that bites can occur quickly. The Mozambique spitting cobra (Naja mossambica) relies primarily on its ability to spit rather than strike as its defence mechanism. Since most bites from N. mossambica occur in sleeping humans, it is likely that while actively foraging at night, they mistakenly bite people. The behavioural results provide perspective into the activity of African snakes and the human-snake interactions that lead to snakebite incidences. Evaluating the extent of overlap between people and wildlife is crucial for the conservation of biodiversity and ecological services. Snakebite prevention should be the main priority over treatment, and management procedures can be beneficial in reducing the risk of interactions between humans and snakes. This thesis provides a framework that ranges from broad to specific, focusing on the ecological drivers of snakebite incidences in South Africa and highlighting important considerations for future research. An ecosystem approach is needed to address snakebite, and I propose that large-scale education campaigns should be implemented in South Africa to mitigate snakebite incidences. These findings provide insight into creating protocols for snakebite management and implementation of education and prevention measures.