Epidemiology and clinical features of Hypnale nepa (hump-nosed pit viper) envenoming in Sri Lanka.

Sri Lanka homes 3 species of hump-nosed pit vipers including Hypnale Hypnale, H. zara and H. nepa from which, latter 2 are endemic to the country. Even though former 2 are the subject of several publications, no major clinical studies have been done regarding H. nepa bites. As these snakes confine only to central hills of the country, their bites are very rare. The objectives of this study were to describe epidemiological and clinical features of H. nepa bites. A prospective observational study was conducted for patients admitted with H. nepa bites to Teaching Hospital, Ratnapura, Sri Lanka for 5 years commencing from June 2015. Species identification was done using a standard key. There were 14 (3.6%) patients with H. nepa bites of which 9 (64%) were males and 5 (36%) were females. Their age ranged from 20 to 73 years (median 37.5). Seven bites (50%) occurred on lower limbs. Majority of bites (10; 71%) happened at daytime [0600-1759 h] in tea estates (8; 57%). Most patients (8; 57%) were admitted within 1-3 h from bite. Hospital stay was 2.5 days (IQR 2-3). Local envenoming was observed in all patients including local pain and swelling [mild (7; 50%), moderate (5; 36%), severe (2; 14%)], local bleeding (1; 7%) and lymphadenopathy (1; 7%). Nonspecific features were observed in 3 (21%). Systemic manifestations were found in 2 (14%) including microangiopathic haemolytic anaemia and sinus bradycardia. Two (14%) had myalgia. H. nepa bites frequently cause local envenoming. But, rarely systemic manifestations may occur.