Neurotoxicity in Russell’s viper (Daboia russelii) envenoming in Sri Lanka: a clinical and neurophysiological study

Abstract

Context: Russell’s viper is more medically important than any other Asian snake, due to number of envenoming’s and fatalities. Russell’s viper populations in South India and Sri Lanka (Daboia russelii) cause unique neuromuscular paralysis not seen in other Russell’s vipers. Objective: To investigate the time course and severity of neuromuscular dysfunction in definite Russell’s viper bites, including antivenom response. Methodology: We prospectively enrolled all patients (>16 years) presenting with Russell’s viper bites over 14 months. Cases were confirmed by snake identification and/or enzyme immunoassay. All patients had serial neurological examinations and in some, single fibre electromyography (sfEMG) of the orbicularis oculi was performed. Results: 245 definite Russell’s viper bite patients (median age: 41 years; 171 males) presented a median 2.5 h (interquartile range: 1.75–4.0 h) post-bite. All but one had local envenoming and 199 (78%) had systemic envenoming: coagulopathy in 166 (68%), neurotoxicity in 130 (53%), and oliguria in 19 (8%). Neurotoxicity was characterised by ptosis (100%), blurred vision (93%), and ophthalmoplegia (90%) with weak extraocular movements, strabismus, and diplopia. Neurotoxicity developed within 8 h post-bite in all patients. No bulbar, respiratory or limb muscle weakness occurred. Neurotoxicity was associated with bites by larger snakes (p < 0.0001) and higher peak serum venom concentrations (p = 0.0025). Antivenom immediately decreased unbound venom in blood. Of 52 patients without neurotoxicity when they received antivenom, 31 developed neurotoxicity. sfEMG in 27 patients with neurotoxicity and 23 without had slightly elevated median jitter on day 1 compared to 29 normal subjects but normalised thereafter. Neurological features resolved in 80% of patients by day 3 with ptosis and weak eye movements resolving last. No clinical or neurophysiological abnormality was detected at 6 weeks or 6 months. Conclusion: Sri Lankan Russell’s viper envenoming causes mild neuromuscular dysfunction with no long-term effects. Indian polyvalent antivenom effectively binds free venom in blood but does not reverse neurotoxicity.

Keywords:

• Antivenom
• Daboia russelii
• paralysis
• single fibre electromyography

Acknowledgements

We thank the consultant physicians, Anoma Bandaranayake and N. M. Perera for their fullest support throughout this study. Shashika Vithanage, Samadhi Rajapakshe, Thulya Sumanathilake, Aradhana Tennakoon, Pradeep Athukorala, Prasad Ranasinghe, Dharshana Kumara, Malinda Karasinghe, Sampath Wijewardena, Sumedha Chandrasekara, Tharaka Wickramage, Sarasi Kaviratne, Ruwanthi Ranaweera, Dilushi Galagedara for assisting with clinical data collection, Umesh Chathuranga, Dilani Pinnaduwa, Shahmy Sayed, and Fahim Mohamed for assisting with logistics (South Asian Clinical Toxicology Research Collaboration), medical and nursing staff of the teaching hospital – Anuradhapura, staff of the Department of Parasitology, Faculty of Medicine and Allied Sciences – Rajarata University of Sri Lanka. Margaret O’Leary (University of Newcastle) for the help in enzyme-immunoassays. Supun Wellapuliarachchi (Rajarata University of Sri Lanka) is acknowledged for providing the picture in Figure 1.

Disclosure statement

The authors report no declarations of interests.

Funding information

This study was funded by the National Health and Medical Research Council (NHMRC) grant no.: 1030069.