Anjana Silva

Epidemiology and clinical effects of Hump-nosed pit viper (Genus: Hypnale) envenoming in Sri Lanka

Hump-nosed pit vipers of Genus Hypnale are the commonest cause of snake bite in Sri Lanka. Although there are many reports of local effects, coagulopathy and acute kidney injury, it remains unclear how frequent these clinical effects are and therefore the medical importance of this snake genus. The genus has been recently revised to include Hypnale hypnale from Sri Lanka and Western Ghats of Southern India, and the two endemic species to Sri Lanka, Hypnale zara and Hypnale nepa. This was a prospective hospital-based clinical study of definite Hypnale spp. bites from July 2008 to July 2010 in six Sri Lankan hospitals. There were 114 patients included and all snakes were correctly identified by hospital staff as Hypnale spp. Of these, 93 snakes were identified as H. hypnale by an expert, 16 as H. zara and five as H. nepa. Most bites occurred on the lower limbs in the daytime. There was no difference in the clinical effects between the three species. Pain and fang marks were present in all patients, 101 had local swelling and only 16 (14%) developed extensive local swelling that spread proximally and involved more than half of the bitten limb. Systemic symptoms occurred in 18 patients; four patients had an abnormal 20 min whole blood clotting test and one patient developed an acute kidney injury that required haemodialysis. All patients were discharged alive with a median length of stay of 2 days. This study confirms that hump-nosed viper bites cause only minor effects in most cases. Future studies need to undertake formal coagulation studies and identify important early indicators of renal impairment.

Neuromuscular Effects of Common Krait (Bungarus caeruleus) Envenoming in Sri Lanka.

Objective We aimed to investigate neurophysiological and clinical effects of common krait envenoming, including the time course and treatment response. Methodology Patients with definite common krait (Bungarus caeruleus) bites were recruited from a Sri Lankan hospital. All patients had serial neurological examinations and stimulated concentric needle single-fibre electromyography (sfEMG) of orbicularis oculi in hospital at 6wk and 6–9mth post-bite. Principal Findings There were 33 patients enrolled (median age 35y; 24 males). Eight did not develop neurotoxicity and had normal sfEMG. Eight had mild neurotoxicity with ptosis, normal sfEMG; six received antivenom and all recovered within 20–32h. Seventeen patients developed severe neurotoxicity with rapidly descending paralysis, from ptosis to complete ophthalmoplegia, facial, bulbar and neck weakness. All 17 received Indian polyvalent antivenom a median 3.5h post-bite (2.8–7.2h), which cleared unbound venom from blood. Despite this, the paralysis worsened requiring intubation and ventilation within 7h post-bite. sfEMG showed markedly increased jitter and neuromuscular blocks within 12h. sfEMG abnormalities gradually improved over 24h, corresponding with clinical recovery. Muscle recovery occurred in ascending order. Myotoxicity was not evident, clinically or biochemically, in any of the patients. Patients were extubated a median 96h post-bite (54–216h). On discharge, median 8 days (4–12days) post-bite, patients were clinically normal but had mild sfEMG abnormalities which persisted at 6wk post-bite. There were no clinical or neurophysiological abnormalities at 6–9mth. Conclusions Common krait envenoming causes rapid onset severe neuromuscular paralysis which takes days to recover clinically consistent with sfEMG. Subclinical neuromuscular dysfunction lasts weeks but was not permanent. Antivenom effectively cleared venom but did not prevent worsening or reverse neuromuscular paralysis.

Efficacy of Indian polyvalent snake antivenoms against Sri Lankan snake venoms: lethality studies or clinically focussed in vitro studies

In vitro antivenom efficacy studies were compared to rodent lethality studies to test two Indian snake antivenoms (VINS and BHARAT) against four Sri Lankan snakes. In vitro efficacy was tested at venom concentrations consistent with human envenoming. Efficacy was compared statistically for one batch from each manufacturer where multiple vials were available. In binding studies EC50 for all VINS antivenoms were less than BHARAT for D. russelii [553 μg/mL vs. 1371 μg/mL;p = 0.016), but were greater for VINS antivenoms compared to BHARAT for N. naja [336 μg/mL vs. 70 μg/mL;p < 0.0001]. EC50 of both antivenoms was only slighty different for E. carinatus and B. caeruleus. For procoagulant activity neutralisation, the EC50 was lower for VINS compared to BHARAT - 60 μg/mL vs. 176 μg/mL (p < 0.0001) for Russell’s viper and 357 μg/mL vs. 6906μg/mL (p < 0.0001) for Saw-scaled viper. Only VINS antivenom neutralized in vitro neurotoxicity of krait venom. Both antivenoms partially neutralized cobra and didn’t neutralize Russell’s viper neurotoxicity. Lethality studies found no statistically significant difference in ED50 values between VINS and BHARAT antivenoms. VINS antivenoms appeared superior to BHARAT at concentrations equivalent to administering 10 vials antivenom, based on binding and neutralisation studies. Lethality studies were inconsistent suggesting rodent death may not measure relevant efficacy outcomes in humans.

Revisiting Russell's viper (Daboia russelii) bite in Sri Lanka: is abdominal pain an early feature of systemic envenoming?

The Russells viper (Daboia russelii) is responsible for 30–40% of all snakebites and the most number of life-threatening bites of any snake in Sri Lanka. The clinical profile of Russells viper bite includes local swelling, coagulopathy, renal dysfunction and neuromuscular paralysis, based on which the syndromic diagnostic tools have been developed. The currently available Indian polyvalent antivenom is not very effective in treating Russells viper bite patients in Sri Lanka and the decision regarding antivenom therapy is primarily driven by clinical and laboratory evidence of envenoming. The non-availability of early predictors of Russells viper systemic envenoming is responsible for considerable delay in commencing antivenom. The objective of this study is to evaluate abdominal pain as an early feature of systemic envenoming following Russells viper bites. We evaluated the clinical profile of Russells viper bite patients admitted to a tertiary care centre in Sri Lanka. Fifty-five patients were proven Russells viper bite victims who produced the biting snake, while one hundred and fifty-four were suspected to have been bitten by the same snake species. Coagulopathy (159, 76.1%), renal dysfunction (39, 18.7%), neuromuscular paralysis (146, 69.9%) and local envenoming (192, 91.9%) were seen in the victims, ranging from mono-systemic involvement to various combinations. Abdominal pain was present in 79.5% of these patients, appearing 5 minutes to 4 hours after the bite. The severity of the abdominal pain, assessed using a scoring system, correlated well with the severity of the coagulopathy (p<0.001) and the neurotoxicity (p<0.001). Its diagnostic validity to predict systemic envenoming is – Sensitivity 81.6%, Specificity 82.4%, Positive predictive value 91.2%. Thus, abdominal pain is an early clinical feature of systemic Russells viper bite envenoming in Sri Lanka. However, it is best to judge abdominal pain together with other clinical manifestations on decision making.

Acute Myocardial Infarction following a possible direct intravenous bite of Russell’s viper ( Daboia russelli )

BackgroundRussell’s viper (Daboia russelli) bites lead to high morbidity and mortality in South Asia. Although variety of clinical manifestations is reported in viper bite victims, myocardial ischemic events are rare.Case presentationWe report a unique case of inferior wall ST elevation myocardial infarction due to a Russell’s viper bite over a vein with possible direct intravenous envenoming, in a young male with no past history or family history suggestive of ischemic cardiac disease, from Sri Lanka. In addition, the possible mechanisms of myocardial ischemia in snake bite victims are also briefly discussed.ConclusionImportance of the awareness of physicians on the rare, yet fatal manifestations of snake envenoming is highlighted.

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.

Hump-nosed pit viper (Hypnale hypnale) envenoming causes mild coagulopathy with incomplete clotting factor consumption

Context. Limited information exists on the coagulopathy caused by hump-nosed pit viper (Hypnale hypnale) envenoming. Objectives. This study aimed to characterise the coagulopathy in hump-nosed pit viper bites by measuring laboratory clotting times and factor studies. Materials and methods. Cases of hump-nosed pit viper envenoming were included from a prospective cohort study of Sri Lankan snake-bite patients. Patient age, sex, snake identification, time of bite and clinical effects were recorded. Patients did not receive anti-venom because no specific anti-venom to hump-nosed vipers exists. All patients received supportive care and serial 20-min whole blood clotting tests (WBCT20). The prothrombin time (PT), international normalised ratio (INR), activated partial thromboplastin time (aPTT), coagulation factors I, II, V, VII, VIII, IX and X, von Willebrand factor (vWF) antigen and D-Dimer concentrations were measured. The median of highest or lowest test result for each patient was reported with interquartile range (IQR). Results. There were 80 hump-nosed pit viper bites, median age was 37 years (IQR: 26–51 years) and 48 were male. The WBCT20 was positive in one patient. The median highest INR was 1.9 (1.5–2.2; Range: 1.3 to > 12) and median highest aPTT was 54 s (46–72 s; Range: 35–170 s). There was low fibrinogen [median: 1.3 g/L;1, –1.8 g/L; Range: < 0.2–2.9], low factor VIII levels [median: 23%; 16–37%] and low factor V levels [median: 43%; 23–74%]. D-Dimer concentrations [median: 3.4 mg/L; 2–7.4 mg/L] were slightly elevated. Factors II, VII and X and vWF antigen concentrations were normal. Discussion and Conclusions. Hump-nosed pit viper bites result in a mild coagulopathy which is usually not detected by a WBCT20. It is characterised by mild elevation of INR, low fibrinogen and Factors V and VIII which may be consistent with the venom containing a thrombin-like enzyme.

Molecular identification of potential leishmaniasis vector species within the Phlebotomus (Euphlebotomus) argentipes species complex in Sri Lanka

BackgroundLeishmaniasis is an emerging vector-borne disease in Sri Lanka. Phlebotomus (Euphlebotomus) argentipes sensu lato Annandale and Brunette 1908 is suspected to be a potential vector. Three sibling species have been reported in the species complex based on analysis of morphological data. A study was carried out in different parts of Sri Lanka including cutaneous leishmaniasis prevailing localities to characterise the sibling species of Phlebotomus (Euphlebotomus) argentipes sensu lato and to establish their possible role in Leishmania transmission.MethodsSandflies were collected using cattle baited trap nets and mouth aspirator. They were identified based on existing taxonomic keys. Sequences of amplified cytochrome oxidase subunit I (CO I), cytochrome oxidase b (cyt b), internal transcribed spacer 2 (ITS2), 18s and 28s rDNA regions were analysed to confirm the number of sibling species. Vectorial capacity of the sibling species was checked by detecting human and Leishmania DNA.ResultsSandflies collected using different techniques were processed for identification, parasite detection and molecular characterization. The 18s, 28s rDNA and cytochrome oxidase subunit I (CO I), internal transcribed spacer 2 (ITS2) and cytochrome b oxidase (cytb) sequences confirmed that the species belonged to the Argentipes complex. 18s and 28s sequences did not show any variation among the proposed sibling species. The phylogeny created from mitochondrial CO I and cytochrome b data and from the nuclear ITS2 region supports the existence of only two groups of flies (termed A and B) from Phlebotomus (Euphlebotomus) argentipes complex instead of the previously proposed three. The Leishmania mini-circle kinetoplastid, heat shock protein 70 (hsp70) and internal transcribed spacer I DNA along with human blood were detected from sibling species A only, which has not previously been considered to be a vector.ConclusionsThe taxonomy of the Sri Lankan Argentipes species complex is reassessed based on the molecular data. The existence of two sibling species is proposed; sibling species A has a long sensilla chaetica (> 50% length of the second antennal flagellomere) and sibling species B has a short sensilla cheatica (< 50%). Sibling species A is incriminated as a vector for leishmaniasis in Sri Lanka.

Cross-Neutralisation of In Vitro Neurotoxicity of Asian and Australian Snake Neurotoxins and Venoms by Different Antivenoms

There is limited information on the cross-neutralisation of neurotoxic venoms with antivenoms. Cross-neutralisation of the in vitro neurotoxicity of four Asian and four Australian snake venoms, four post-synaptic neurotoxins (α-bungarotoxin, α-elapitoxin-Nk2a, α-elapitoxin-Ppr1 and α-scutoxin; 100 nM) and one pre-synaptic neurotoxin (taipoxin; 100 nM) was studied with five antivenoms: Thai cobra antivenom (TCAV), death adder antivenom (DAAV), Thai neuro polyvalent antivenom (TNPAV), Indian Polyvalent antivenom (IPAV) and Australian polyvalent antivenom (APAV). The chick biventer cervicis nerve-muscle preparation was used for this study. Antivenom was added to the organ bath 20 min prior to venom. Pre- and post-synaptic neurotoxicity of Bungarus caeruleus and Bungarus fasciatus venoms was neutralised by all antivenoms except TCAV, which did not neutralise pre-synaptic activity. Post-synaptic neurotoxicity of Ophiophagus hannah was neutralised by all antivenoms, and Naja kaouthia by all antivenoms except IPAV. Pre- and post-synaptic neurotoxicity of Notechis scutatus was neutralised by all antivenoms, except TCAV, which only partially neutralised pre-synaptic activity. Pre- and post-synaptic neurotoxicity of Oxyuranus scutellatus was neutralised by TNPAV and APAV, but TCAV and IPAV only neutralised post-synaptic neurotoxicity. Post-synaptic neurotoxicity of Acanthophis antarcticus was neutralised by all antivenoms except IPAV. Pseudonaja textillis post-synaptic neurotoxicity was only neutralised by APAV. The α-neurotoxins were neutralised by TNPAV and APAV, and taipoxin by all antivenoms except IPAV. Antivenoms raised against venoms with post-synaptic neurotoxic activity (TCAV) cross-neutralised the post-synaptic activity of multiple snake venoms. Antivenoms raised against pre- and post-synaptic neurotoxic venoms (TNPAV, IPAV, APAV) cross-neutralised both activities of Asian and Australian venoms. While acknowledging the limitations of adding antivenom prior to venom in an in vitro preparation, cross-neutralization of neurotoxicity means that antivenoms from one region may be effective in other regions which do not have effective antivenoms. TCAV only neutralized post-synaptic neurotoxicity and is potentially useful in distinguishing pre-synaptic and post-synaptic effects in the chick biventer cervicis preparation.

Dangerous snakes, deadly snakes and medically important snakes

This correspondence argues that the dangerousness of a venomous snake species is not solely determined by the venom characteristics or the lethality of the snake, and recognizes that medical importance comprises a key variable as well. The medical importance of a snake is determined by several factors – including frequency of medical attention after a bite, local or systemic envenomation provoked by the bite, fatal bites, long term consequences, availability of antivenom therapy as well as the size of the population at risk – that may vary from one region to another.