title: Clinical, epidemiological and electrophysiological aspects of envenoming by the Papuan taipan (Oxyuranus scutellatus canni)
Creators: name: Trevett, Andrew James
Publisher: name: University of Glasgow
Year: 1994
Subjects: subject: Epidemiology, Medicine.

description: The purpose of the work described in this thesis was to further knowledge about the circumstances and effects of envenoming by the Papuan taipan (Oxyuranus scutellatus canni) and to determine how morbidity and mortality can be reduced. My specific aims have included analysis of the epidemiology of taipan bite, of first aid treatment and of the efficacy of current antivenom treatment. I have also determined the in vivo electrophysiological effects of the neurotoxins in taipan venom and applied these observations to assess drugs of potential benefit in the treatment of envenomed patients. The development of enzyme linked immunoassays (EIA) for the detection of snake venom antigen has enabled retrospective identification of biting species, has provided the opportunity to make reliable species specific observations and has helped to define the epidemiology of snakebite. In this study, EIAs were used to identify definitive taipan bites from a prospective series of all snakebite victims admitted to PMGH between May 1991 and May 1993. All patients with signs of systemic envenoming were managed according to treatment guidelines contained in standard treatment books published by the Papua New Guinea Department of Health. The circumstances of the bite and all clinical details were recorded on a proforma. Electrophysiological studies were done on selected patients with neurotoxicity who were believed on clinical grounds to have been bitten by a taipan. The results of these studies were compared with similar studies done in a group of volunteer Melanesian controls. A subset of the envenomed patients with established neurotoxicity was included in studies looking at the effects of edrophonium and 3,4-diaminopyridine. Patients were included in this study if taipan venom antigen was detected at a significant level in one or more of: an admission serum sample, a bite site aspirate or a swab of the bite site. One hundred and seventeen patients were included in the epidemiological analysis, 106 in the clinical study and smaller numbers in each of the electrophysiological studies. The taipan was confirmed to be the species accounting for the majority of cases of significant envenoming in Central Province. Between 1991 and 1993, 89% of envenomed patients admitted to PMGH in whom a definitive identification of biting species was made, were bitten by a taipan. The Papuan black snake (Pseudechis papuanus), which is widely feared and believed by most lay people and many medical staff to be the most numerous and dangerous species in Central Province, accounted for less than 1% of bites. This suggests a change in the herpetofauna of the Province over the past 30 years and has significant implications for the use of monovalent antivenoms. There is little role for the continued use of monovalent black snake antivenom in Papua New Guinea, polyvalent antivenom is a better option if a black snake bite is considered a possibility. Virtually all taipan bites occurred during daylight hours in low lying coastal parts of the Province, predominantly in Eucalyptus savannah. Few patients were able to describe distinguishing features of the snake that bit them. The majority of patients envenomed by a taipan had non-clotting blood by the time they reached a medical facility and this sign has a predictive value of over 95% for taipan bite in Central Province. Despite the majority receiving antivenom, 46.7% of patients progressed to require intubation and ventilation. Antivenom was of maximal value if given within 4 hours of envenoming but even early antivenom did not prevent progression of neurotoxicity in a high proportion of patients. Antivenom appeared to hasten the resolution of coagulopathy in envenomed patients but there was little evidence that this produced a significant clinical advantage. Envenomed patients had normal sensory and motor conduction velocities but showed markedly reduced evoked compound muscle action potentials and slightly reduced sensory nerve action potentials. There was a decremental response on repetitive nerve stimulation testing, enhanced by exercise or tetanic stimulation. These findings are consistent with neuromuscular block localised to the synapse. Electrophysiological studies provide an objective basis for studying the effects of pharmacological interventions in snakebite patients with neurotoxicity, but neither edrophonium or 3,4- diaminopyridine can be recommended for the treatment of patients envenomed by the Papuan taipan. (Abstract shortened by ProQuest.).