Clinico-epidemiology of Hypnale zara (hump-nosed pit viper) envenoming in Sri Lanka

BACKGROUND

Hump-nosed vipers of the genus Hypnale are the most common cause of venomous snakebites in Sri Lanka. The genus includes three species: Hypnale hypnale, Hypnale zara and Hypnale nepa. Of them, H. hypnale bites are the most common and are the subject of many publications. The epidemiology and clinical features of bites by the other two species have been less investigated.

METHODS

We conducted a prospective observational study of H. zara bites from January 2015 to June 2020 at the Teaching Hospital, Ratnapura, Sri Lanka. Data were collected for 5.5 years in the wet zone of the island, where the principal investigator did assessment of all patients and the data collection.

RESULTS

H. zara envenoming was confirmed through identification of dead or live snake specimens brought with the patients. Of the 480 patients with proven hump-nosed viper bites, H. zara bites accounted for 105 (22%), including dry bites (n=5 [5%]) and envenoming (n=100 [95%]), with gender distribution of 65 (62%) males and a mean age of 43.1 y. Most bites occurred on the lower limbs (n=71 [68%]) in the daytime (n=69 [66%]) in home gardens (n=45 [43%]). A total of 100 (95%) patients had local manifestations, including pain (n=100 [95%]), swelling (n=100 [95%]), bleeding (n=20 [19%]), bruising (n=11 [10%]), lymphadenopathy (n=10 [9%]), necrosis at the bite site (n=9 [9%]) and blistering (n=8 [8%]). Seven (6.7%) patients showed systemic effects, including acute kidney injury (n=2 [2%]), microangiopathic haemolysis (n=2 [2%]), sinus bradycardia (2 [2%]) and one (1%) each had coagulopathy, thrombotic microangiopathy, Kounis syndrome and ischaemic changes on electrocardiography. Eosinophilia was a significant haematological finding (n=26 [25%]) and 16 (15%) had leucocytosis and 15 (14%) had neutrophilia. Ninety six percent of patients (n=101) recovered. Antivenom is not available for hump-nosed viper bites in Sri Lanka and therefore patients were managed conservatively.

CONCLUSIONS

This study shows that H. zara bites mainly cause local envenoming and rarely systemic effects.

Hump-nosed pit viper (Hypnale hypnale and Hypnale zara) envenoming in Deniyaya, Sri Lanka: Epidemiological and clinical features from a prospective observational study

Hypnale hypnale, Hypnale zara and Hypnale nepa are the three species of Hump nosed pit vipers that are implicated in human bites in Sri Lanka. H. zara and H. nepa are two endemic species to the country. The objective of the study was to characterize epidemiology and clinical features after different Hump nosed pit viper species bites. A prospective observational study was conducted in Base Hospital Deniyaya from 2013 to 2015. Hump nosed pit viper as the offending snake was identified when the victims brought live or dead specimens. Species identification of dead specimen was done by a herpetologist. Clinical details were recorded during the hospital stay. 83 Hump nosed pit viper bite patients (19-81 years) were studied. Fifty two dead specimens were identified as 39 of H. zara and 13 of H. hypnale by the herpetologist. No H. nepa was identified. Thirty one live snakes were identified as Hump nosed pit vipers and released in to the wild. Envenoming was reported throughout the year. Eighty (96.4%) were daytime bites. Hands (43.4%), feet (55.4%) and arms (1.2%) were affected sites. Sixty two (74.7%) were bitten in tea plantations. All had pain over bite site. Overall, sixty nine (83.1%) had local swelling, seven (8.4%) extensive limb swelling, nineteen (22.9%) haemorrhagic blisters, and seven (8.4%) regional lymphadenopathy. Four (4.8%) patients had incoagulable blood by 20WBCT. H. zara bites had 28.2% haemorrhagic blisters, 7.7% extensive limb swelling and 2.6% coagulopathy. H. hypnale bites had 7.7% each extensive limb swelling and coagulopathy and 23.1% haemorrhagic blisters. None developed elevated serum creatinine. Neurotoxicity was not noted. Hump nosed pit viper bites caused substantial morbidity. Risk factors included day time outdoor activities and occupation. Pain, extensive limb swelling, bite site swelling, haemorrhagic blisters, regional lymphadenopathy and coagulopathy were prominent clinical features. Nephrotoxicity and neurotoxicity were notably absent. Clinical features varied depending on the species implicated.

Venom-Induced Consumption Coagulopathy Following Hump-Nosed Pit Viper (Genus: Hypnale) Envenoming in Sri Lanka: Uncertain Efficacy of Fresh Frozen Plasma

INTRODUCTION

Hump-nosed pit vipers (Hypnale spp) cause the highest number of venomous snakebites in Sri Lanka. Bites commonly cause local envenoming leading to local pain, swelling, and necrosis of the site of the bite. Acute kidney injury is the most common systemic manifestation, and some patients develop venom-induced consumption coagulopathy (VICC). Genus Hypnale comprises 3 species. Of them, H hypnale is found in Sri Lanka and the Western Ghats region of India. The other 2 (H nepa and H zara) are endemic species in Sri Lanka.

METHODS

This study included 500 patients with hump-nosed viper bites studied prospectively over 4.5 y starting June 2014. All patients were assessed and the data were collected by the principal investigator (primary data). A subgroup of patients who developed VICC is described. There were 2 groups, including proven (patients with the specimen of the snake) and probable (specimen of snake not available) bites.

RESULTS

Thirty (n=500; 6%) patients developed VICC; of them, 17 (3%) were proven cases, and 13 (2%) were probable cases. In both groups, 24 (80%) recovered, 2 (7%) progressed to chronic kidney disease, 1 (3%) died of severe hemostatic dysfunction, and 3 (10%) were lost to follow-up. Systemic bleeding was observed in 16 patients (53%), including hematuria (microscopic and gross) in 8 (27%) and venipuncture bleeding in 5 (17%). Eleven (37%) developed local bleeding at the site of the bite. Fresh frozen plasma was administered to 20 patients (67%), among whom only 11 (55%) experienced early correction of VICC. In both groups, 15 (50%) developed acute kidney injury, and 2 (7%) progressed to chronic kidney disease. Microangiopathic hemolysis was observed in 18 patients (60%) and thrombocytopenia in 16 (53%). Thrombotic microangiopathy was detected in 13 patients (43%), of whom 10 (33%) developed hemolytic uremic syndrome and 2 (7%) had thrombotic thrombocytopenic purpura. Of patients with VICC in the proven group, 94% (n=16) was caused by H hypnale and 1 (6%) was caused by H zara. In the proven group, median international normalized ratio was 3.7 (interquartile range 1.6-5.0); in the probable group, it was 5.0 (interquartile range 2.1-5.4).

CONCLUSIONS

We found that 6% of patients develop hemostatic dysfunction after hump-nosed viper bites. However, which patients will develop coagulopathy or die of envenoming is unpredictable. Reliable and accessible treatments are unmet essential needs because antivenoms for these bites are currently not available in the country. Therapy with fresh frozen plasma has doubtful efficacy in early correction of VICC and needs further evaluation.