First clinical experiences about the neurotoxic envenomings inflicted by lowland populations of the Balkan adder, Vipera berus bosniensis

The first overall clinical description of envenomings by the lowland populations of the Balkan adder (Vipera berus bosniensis) is provided by this study. Fifty-four incidents have been collected retrospectively from the south-western Hungarian and the northern Croatian distribution area of the taxon. There were five (9%) asymptomatic, 24 (44%) mild, 12 (22%) moderate, 12 (22%) severe, and one fatal (2%) case according to the Poisoning Severity Score. The single death is a 60-year-old Hungarian case that was caused by V.b. bosniensis. Average hospitalisation was 2.75 days. The most common systemic symptoms were gastrointestinal disorders, ECG changes, persisting hypotension and neurological disorders. The initial phase of neurotoxic manifestations was always expressed in cranial nerve disturbances: ptosis, external ophthalmoplegia, diplopia, reduced focusing capability and blurred vision. Neuromuscular paralysis progressed to dyspnoea and lower limb paralysis in the most severe cases. Unusual symptoms were fluctuating arterial hypertension, drowsiness, and hypokalaemia. Laboratory results reveal leucocytosis, while deviation in the other laboratory values is not common. Envenomings by V.b. bosniensis significantly differ from those by the European adder (Vipera berus berus) in lower manifestation rate of extensive oedema, anaemia, CNS depression, and haematuria but the development of neuromuscular paralysis is high (20%). Their bites rather resulted in mild and moderate local symptoms in envenomed patients than those inflicted by the nominate form. This study presents the evidence of the frequent neurotoxic manifestations in Balkan adder-bitten patients for the first time, which strongly suggests that the venom of the lowland populations of V.b. bosniensis has neurotoxic activity.