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Abstract:
Snakebite is an important medical emergency in rural Nepal. Correct identification of the biting species is crucial for clinicians to choose appropriate treatment and anticipate complications. This is particularly important for neurotoxic envenoming which, depending on the snake species involved, may not respond to available antivenoms. Adequate species identification tools are lacking. This study used a combination of morphological and molecular approaches (PCR-aided DNA sequencing from swabs of bite sites) to determine the contribution of venomous and non-venomous species to the snakebite burden in southern Nepal. Out of 749 patients admitted with a history of snakebite to one of three study centres, the biting species could be identified in 194 (25.9%). Out of these, 87 had been bitten by a venomous snake, most commonly the Indian spectacled cobra (Naja naja; n = 42) and the common krait (Bungarus caeruleus; n = 22). When both morphological identification and PCR/sequencing results were available, a 100% agreement was noted. The probability of a positive PCR result was significantly lower among patients who had used inadequate “first aid” measures (e.g. tourniquets or local application of remedies). This study is the first to report the use of forensic genetics methods for snake species identification in a prospective clinical study. If high diagnostic accuracy is confirmed in larger cohorts, this method will be a very useful reference diagnostic tool for epidemiological investigations and clinical studies.
Author Summary:
Snakebite is an important medical problem in sub-tropical and tropical regions, including Nepal where tens of thousands of people are bitten every year. Snakebite can result in life-threatening envenoming, and correct identification of the biting species is crucial for care providers to choose appropriate treatment and anticipate complications. This paper explores a number of methods, including molecular techniques, to assist care providers in identifying the species responsible for bites in rural Nepal. Out of 749 patients with a history of snakebite, the biting species could be identified in 194 (25.9%). Out of these, 87 had been bitten by a venomous snake, most commonly cobras (n = 42) and kraits (n = 22). This study is the first to report the use of molecular techniques for snake species identification. The diagnostic accuracy of this method appears high but needs to be confirmed in larger studies.
Background: Neurotoxic envenomation following bites by kraits (Bungarus species) is a leading cause of snakebite mortality in South Asia. Over a long time, this had been attributed only to one species, the common krait (Bungarus caeruleus). However, recent research has provided increasing evidence of the involvement of several krait species. Here, we report a fatal case of neurotoxic envenomation following the bite of a greater black krait (Bungarus niger) in Nepal.
Case presentation: A 33-year-old man was bitten in the outdoor corridor of his home in the eastern hills of Ilam district while handling a snake he thought to be non-venomous. He subsequently developed severe abdominal pain, frequent vomiting, and signs of neurotoxic envenomation leading to respiratory paralysis. The patient did not respond to Indian polyvalent antivenom given 4 h after the bite and died under treatment 8 h after the bite. This is the second time that a B. niger was observed in Nepal, the first documented case of envenomation by this species in the country and the sixth reported case worldwide.
Conclusions: Previous distribution records – from eastern India and western Nepal, from western hills in Nepal, and from lowland localities in India and Bangladesh – indicate risk of envenomation by B. niger throughout the low and intermediate elevations of Nepal up to at least 1,500 m above sea level. As very few people in Nepal bring killed snakes to healthcare centers and because there is a general belief among local people that there are no kraits in the hills, bites by B. niger are likely to be misdiagnosed and underreported.