GLOBAL SNAKEBITE EPIDEMIOLOGY

Janaka de Silva,

Department of Medicine, Faculty of Medicine, University of Kelaniya, Ragama, Sri Lanka

Abstract Snakebite envenoming is a significant cause of global morbidity and mortality. The problem is particularly important in tropical and subtropical countries in Africa, Asia, Oceania and Latin America. Most morbidity and mortality occurs in the rural tropics, and results in high medical and, very likely, an economic toll as the victims are usually productive young adults. The true global incidence of snakebite envenoming and mortality remains largely unknown. The main reason being the few reliable data available from the worst affected regions. There have been three major attempts at estimating the global burden of snakebite. The most recent one, in 2008, estimates there to be 1.2 to 5.5 million bites, 420,000 to 1.8 million envenomings and 20,000 to 94,000 deaths due to snakebite per year, globally. The burden is highest in South and Southeast Asia and sub-Saharan Africa.

The wide ranges in the numbers given in these estimates reflect the many difficulties associated with obtaining accurate data on snakebite: Firstly, snake envenoming is a disease of the poor, with a clear negative association between snakebite deaths and state expenditure on health. The burden is highest in countries least able to deal with the cost of snakebite, resulting in recording systems being unavailable or unreliable. Secondly, seasonal and geographical variations in bites, even within small countries, when extrapolated to the entire country or region are bound to be inaccurate. Thirdly, Hospital data on snakebites are likely to be underestimates as many victims do not seek hospital treatment and prefer traditional remedies. Studies from rural Nigeria and Kenya have reported that only 8.5% and 27% of snakebite victims, respectively, sought hospital treatment. In a rural district in Sri Lanka, hospital statistics did not report 62.5% of the true number of snakebite deaths.

Studies on snakebite epidemiology are, at present, mostly confined to obtaining the numbers of bites, envenomings and deaths. There are few reliable data on the long-term physical and psychological disability of those surviving snakebite, and their economic consequences. A recent Sri Lankan study showed subclinical nerve conduction abnormalities in many victims of elapid bites who had presented with neurotoxicity 12 months previously. Another has shown significant delayed psychological morbidity among snakebite victims who had systemic envenoming 12 to 48 months previously. Over a quarter of them claimed that the snakebite had caused a negative change in their employment. The impact of chronic disability due to snakebite is, therefore, an urgent area for future research.