Snakebite in tropical Australia: a prospective study in the "Top End" of the Northern Territory

Snakebite envenoming: A systematic review and meta-analysis of global morbidity and mortality

BACKGROUND

Snakebite envenoming represents a significant and often neglected public health challenge, particularly in rural communities across tropical and subtropical regions. An estimated 1.2-5.5 million people are envenomed by snakebites annually. More than 125,000 of these bites are fatal, and 3-4 times as many results in disability/disfigurement. Despite its prevalence, collecting accurate epidemiological data on snakebite is challenging. This systematic review and meta-analysis collates global epidemiology data on snakebite morbidity and mortality.

METHODS

Medline, Embase, Cochrane and CINAHL Plus databases were searched for articles published between 2001-2022. Pooled incidence and mortality were obtained using random effects modelling, heterogeneity (I2) was tested, and sensitivity analyses performed. Newcastle-Ottawa Scale assessed study quality.

RESULTS

Out of the four databases, 5,312 articles were found. After removing duplicates, 3,953 articles were screened by title and abstract and 65 articles containing information on snakebite epidemiology, encompassing 663,460 snakebites, were selected for analysis. The people most at risk for snakebite were men (59%), engaged in agricultural labour (27.5%), and residing in rural areas (66.7%). More than half (57%) of the reported bites resulted in envenoming. Incidents occurred frequently in the summer season (38.5%), during daytime (56.7%), and bites were most often to the lower limb (56.4%). Envenoming severity was frequently mild (46.7%), treated in hospital (68.3%), and was treated with anti-venom (64.7%). The pooled global incidence and mortality was 69.4 /100,000 population (95%CI: 36.8 to 101.9) and 0.33/100,000 population (95%CI, 0.14 to 0.52) per year, respectively. Stratified by continents, Asia had the highest incidence of 130.7/100,000 population (95%CI: 48.3 to 213.1) while Europe has the lowest with 0.7/100,000 population (95%CI: -0.2 to 1.5). The highest mortality was reported in Asia at 0.96/100,000 population (95% CI: 0.22 to 1.70), and Africa 0.44/100,000 population (95%CI: -0.03 to 0.84). Incidence was highest among inhabitants of lower-middle-income countries 132.7/100,000 population (95%CI: 55.4 to 209.9) while mortality was highest in low-income countries at 0.85/100,000 population (95% CI: -0.06 to 2.31).

CONCLUSION

Incidence and mortality rates noted here highlight the global impact of snakebite and underscore the critical need to address the burden of snakebite envenoming. It also reveals that while reported snakebite incidence was higher in lower-middle-income countries, the burden of mortality was greatest among inhabitants of low-income countries, again emphasising the need for greater efforts to tackle this neglected tropical disease.

The Snake Study: Survey of National Attitudes and Knowledge in Envenomation

Despite recent reviews of best practice for the treatment of Australian venomous bites and stings, there is controversy about some aspects of care, particularly the use of antivenom. Our aim was to understand current attitudes and practice in the management of suspected snake envenoming. A single-stage, cross-sectional survey of Australian emergency care physicians who had treated snake envenomation in the previous 36 months was conducted. Hospital pharmacists were also invited to complete a survey about antivenom availability, usage, and wastage in Australian hospitals. The survey was available between 5 March and 16 June 2019. A total of 121 snake envenoming cases were reported, and more than a third (44.6%) of patients were not treated with antivenom. For those treated with antivenom (n = 67), 29 patients (43%) received more than one ampoule. Nearly a quarter of respondents (21%) identified that antivenom availability was, or could be, a barrier to manage snake envenoming, while cost was identified as the least important factor. Adverse reactions following antivenom use were described in 11.9% of cases (n = 8). The majority of patients with suspected envenoming did not receive antivenom. We noted variation in dosage, sources of information, beliefs, and approaches to the care of the envenomed patient.

Crowdsourcing snake identification with online communities of professional herpetologists and avocational snake enthusiasts

Species identification can be challenging for biologists, healthcare practitioners and members of the general public. Snakes are no exception, and the potential medical consequences of venomous snake misidentification can be significant. Here, we collected data on identification of 100 snake species by building a week-long online citizen science challenge which attracted more than 1000 participants from around the world. We show that a large community including both professional herpetologists and skilled avocational snake enthusiasts with the potential to quickly (less than 2 min) and accurately (69-90%; see text) identify snakes is active online around the clock, but that only a small fraction of community members are proficient at identifying snakes to the species level, even when provided with the snake's geographical origin. Nevertheless, participants showed great enthusiasm and engagement, and our study provides evidence that innovative citizen science/crowdsourcing approaches can play significant roles in training and building capacity. Although identification by an expert familiar with the local snake fauna will always be the gold standard, we suggest that healthcare workers, clinicians, epidemiologists and other parties interested in snakebite could become more connected to these communities, and that professional herpetologists and skilled avocational snake enthusiasts could organize ways to help connect medical professionals to crowdsourcing platforms. Involving skilled avocational snake enthusiasts in decision making could build the capacity of healthcare workers to identify snakes more quickly, specifically and accurately, and ultimately improve snakebite treatment data and outcomes.

Identifying the snake: First scoping review on practices of communities and healthcare providers confronted with snakebite across the world

BACKGROUND

Snakebite envenoming is a major global health problem that kills or disables half a million people in the world's poorest countries. Biting snake identification is key to understanding snakebite eco-epidemiology and optimizing its clinical management. The role of snakebite victims and healthcare providers in biting snake identification has not been studied globally.

OBJECTIVE

This scoping review aims to identify and characterize the practices in biting snake identification across the globe.

METHODS

Epidemiological studies of snakebite in humans that provide information on biting snake identification were systematically searched in Web of Science and Pubmed from inception to 2nd February 2019. This search was further extended by snowball search, hand searching literature reviews, and using Google Scholar. Two independent reviewers screened publications and charted the data.

RESULTS

We analysed 150 publications reporting 33,827 snakebite cases across 35 countries. On average 70% of victims/bystanders spotted the snake responsible for the bite and 38% captured/killed it and brought it to the healthcare facility. This practice occurred in 30 countries with both fast-moving, active-foraging as well as more secretive snake species. Methods for identifying biting snakes included snake body examination, victim/bystander biting snake description, interpretation of clinical features, and laboratory tests. In nine publications, a picture of the biting snake was taken and examined by snake experts. Snakes were identified at the species/genus level in only 18,065/33,827 (53%) snakebite cases. 106 misidentifications led to inadequate victim management. The 8,885 biting snakes captured and identified were from 149 species including 71 (48%) non-venomous species.

CONCLUSION

Snakebite victims and healthcare providers can play a central role in biting snake identification and novel approaches (e.g. photographing the snake, crowdsourcing) could help increase biting snake taxonomy collection to better understand snake ecology and snakebite epidemiology and ultimately improve snakebite management.

The Australian Snakebite Project, 2005-2015 (ASP-20)

OBJECTIVE

To describe the epidemiology, treatment and adverse events after snakebite in Australia.

DESIGN

Prospective, multicentre study of data on patients with snakebites recruited to the Australian Snakebite Project (2005-2015) and data from the National Coronial Information System. Setting, participants: Patients presenting to Australian hospitals with suspected or confirmed snakebites from July 2005 to June 2015 and consenting to participation.

MAIN OUTCOME MEASURES

Demographic data, circumstances of bites, clinical effects of envenoming, results of laboratory investigations and snake venom detection kit (SVDK) testing, antivenom treatment and adverse reactions, time to discharge, deaths.

RESULTS

1548 patients with suspected snakebites were enrolled, including 835 envenomed patients (median, 87 per year), for 718 of which the snake type was definitively established, most frequently brown snakes (41%), tiger snakes (17%) and red-bellied black snakes (16%). Clinical effects included venom-induced consumption coagulopathy (73%), myotoxicity (17%), and acute kidney injury (12%); severe complications included cardiac arrest (25 cases; 2.9%) and major haemorrhage (13 cases; 1.6%). There were 23 deaths (median, two per year), attributed to brown (17), tiger (four) and unknown (two) snakes; ten followed out-of-hospital cardiac arrests and six followed intracranial haemorrhages. Of 597 SVDK test results for envenomed patients with confirmed snake type, 29 (4.9%) were incorrect; 133 of 364 SVDK test results for non-envenomed patients (36%) were false positives. 755 patients received antivenom, including 49 non-envenomed patients; 178 (24%), including ten non-envenomed patients, had systemic hypersensitivity reactions, of which 45 (6%) were severe (hypotension, hypoxaemia). Median total antivenom dose declined from four vials to one, but median time to first antivenom was unchanged (4.3 hours; IQR, 2.7-6.3 hours).

CONCLUSIONS

Snake envenoming is uncommon in Australia, but is often severe. SVDKs were unreliable for determining snake type. The median antivenom dose has declined without harming patients. Improved early diagnostic strategies are needed to reduce the frequently long delays before antivenom administration.

Australian taipan (Oxyuranus spp.) envenoming: clinical effects and potential benefits of early antivenom therapy - Australian Snakebite Project (ASP-25)

CONTEXT

Taipans (Oxyuranus spp.) are medically important venomous snakes from Australia and Papua New Guinea. The objective of this study was to describe taipan envenoming in Australian and its response to antivenom.

METHODS

Confirmed taipan bites were recruited from the Australian Snakebite Project. Data were collected prospectively on all snakebites, including patient demographics, bite circumstances, clinical effects, laboratory results, complications and treatment. Blood samples were taken and analysed by venom specific immunoassay to confirm snake species and measure venom concentration pre- and post-antivenom.

RESULTS

There were 40 confirmed taipan bites: median age 41 years (2-85 years), 34 were males and 21 were snake handlers. Systemic envenoming occurred in 33 patients with neurotoxicity (26), complete venom induced consumption coagulopathy (VICC) (16), partial VICC (15), acute kidney injury (13), myotoxicity (11) and thrombocytopenia (7). Venom allergy occurred in seven patients, three of which had no evidence of envenoming and one died. Antivenom was given to 34 patients with a median initial dose of one vial (range 1-4), and a median total dose of two vials (range 1-9). A greater total antivenom dose was associated with VICC, neurotoxicity and acute kidney injury. Early antivenom administration was associated with a decreased frequency of neurotoxicity, acute kidney injury, myotoxicity and intubation. There was a shorter median time to discharge of 51 h (19-432 h) in patients given antivenom <4 h post-bite, compared to 175 h (27-1104 h) in those given antivenom >4 h. Median peak venom concentration in 25 patients with systemic envenoming and a sample available was 8.4 ng/L (1-3212 ng/L). No venom was detected in post-antivenom samples, including 20 patients given one vial initially and five patients bitten by inland taipans.

DISCUSSION

Australian taipan envenoming is characterised by neurotoxicity, myotoxicity, coagulopathy, acute kidney injury and thrombocytopenia. One vial of antivenom binds all measurable venom and early antivenom was associated with a favourable outcome.

An instructive case of presumed brown snake (Pseudonaja spp.) envenoming

CONTEXT

Several species of medically important Australian elapid snakes are frequently involved in human envenoming. The brown snake group (Pseudonaja spp., 9 species) is most commonly responsible for envenoming including life-threatening or fatal cases. Several Pseudonaja spp. can inflict human envenoming that features minor local effects, but may cause serious systemic venom disease including defibrination coagulopathy, thrombocytopenia, micro-angiopathic hemolytic anemia (MAHA) and, rarely, paralysis. Pseudonaja envenoming is typically diagnosed by history, clinical assessment including occasional active clinical bleeding noted on physical examination (e.g. from venipuncture sites, recent cuts, etc.), and laboratory detection of coagulopathy (prolonged activated partial thromboplastin time [APTT]/INR, elevated D-dimer, afibrinogenemia and thrombocytopenia). Lack of verified identity of the envenoming snake species is a common problem in Australia and elsewhere. Identification and confirmation of the envenoming Australian snake taxon is often attempted with enzyme sandwich immunoassay venom detection kits (SVDKs). However, the SVDK has limited utility due to unreliable specificity and sensitivity when used to detect venoms of some Australian elapids. Antivenom (AV) remains the cornerstone of treatment, although there is debate concerning the recommended dose (1 vs. 2 or more vials) necessary to treat serious Pseudonaja envenoming. Envenomed patients receiving timely treatment uncommonly succumb, but a proportion of seriously envenomed patients may exhibit clinical or laboratory evidence of myocardial insult.

CASE DETAILS

An 88-year-old woman presented her dog to a veterinarian after it had sustained a bite by a witnessed snake, reportedly an eastern brown snake (Pseudonaja textilis, Elapidae). The woman became suddenly confused, and lost consciousness at the veterinary office. After transport to hospital, she denied any contact with the snake, but developed large haematomas at intravenous (i.v.) catheter insertion sites; blood tests revealed a severe defibrination coagulopathy, consistent with envenoming by a brown snake. An SVDK-tested urine sample was negative. A non-contrast CT of her head showed a minor subacute infarction of the left corona radiata. A twelve-lead ECG was normal, but her troponins were mildly elevated (39 ng/L). A diagnosis of brown snake envenoming was made and she received 2 vials of brown snake AV i.v., without adverse incident. Thirty min post AV her Glasgow Coma Score (GCS) had improved from 13 to 15 (normal). At 3.5 h post AV all bleeding from i.v. sites ceased, although her troponin T level peaked at 639 ng/L, supporting a diagnosis of non-ST elevated myocardial infarction (NSTEMI).

DISCUSSION

Severe brown snake envenoming may occur in the absence of a perceived bite, and AV is temporally associated with improvement in clinical findings and coagulopathy. However, severe envenoming by this species can be complicated by cardiovascular events that in the circumstance of incomplete or absent history may confuse the primary diagnosis and affect patient outcome.

Prothrombin activator-like toxin appears to mediate cardiovascular collapse following envenoming by Pseudonaja textilis

Brown snake (Pseudonaja spp.)-induced early cardiovascular collapse is a life-threatening medical emergency in Australia. We have previously shown that this effect can be mimicked in animals and is mediated via the release of endogenous mediators. In the present study, we aimed to purify and characterize the component in Pseudonaja textilis venom which induces cardiovascular collapse following envenoming. The component (fraction 3) was isolated using a combination of techniques including hydroxyapatite and reverse phase chromatography. Fraction 3 (10 or 20 μg/kg, i.v.) produced a rapid decrease in mean arterial pressure (MAP) followed by cardiovascular collapse. Fraction 3-induced early collapse was abolished by prior administration of smaller priming doses of fraction 3 (i.e. 2 and 5 μg/kg, i.v.) or heparin (300 units/kg, i.v.). P. textilis whole venom (1 and 3 μg/ml), but not fraction 3 (1 or 3 μg/ml), induced endothelium-dependent relaxation in isolated rat mesenteric arteries. SDS-PAGE gel indicated the presence of 9-10 protein bands of fraction 3. Using proteomic based analysis some protein bands of fraction 3 were identified as subunits of venom prothrombin activator, pseutarin C of P. textilis venom. Our results conclude that prothrombin activator-like toxin is likely to be a contributor to the rapid collapse induced by P. textilis venom.

The Australian mulga snake (Pseudechis australis: Elapidae): report of a large case series of bites and review of current knowledge

BACKGROUND

The mulga snake (Pseudechis australis) is the largest terrestrial venomous snake in Australia. It is capable of inflicting severe and occasionally fatal envenoming, but there have been few studies of P. australis bites.

OBJECTIVES

To highlight and reinforce the main features of P. australis envenoming and to provide a clearer picture of the epidemiology of bites from this species.

METHODS

Selected case records kept by the Toxinology Dept. (Women's and Children's Hospital, Adelaide, Australia) were reviewed retrospectively to determine definite P. australis bites.

INCLUSION CRITERIA

definite cases where the snake was identified by a competent person and/or lab specimens (bite site/urine) tested positive for "black snake" using CSL snake venom detection kit in a locality within the known range of P. australis, but without sympatry with other Pseudechis spp.

EXCLUSION CRITERIA

where the snake could not be clearly identified under criteria above. Epidemiological and clinical information was recorded and analysed for the definite cases.

RESULTS

A total of 27 cases were identified as definite P. australis bites; there were no fatalities. The median age was 35.5 years (IQR 51-23) and 80% of bites occurred in males. More bites occurred in the warmer months (Dec-March) and in those handling/interfering with snakes. Seven people were bitten whilst asleep at night. 21/27 patients developed systemic envenoming (based on signs, symptoms and laboratory results) and 17 cases received antivenom. Local bite site pain (18) and swelling (17) were common as were non-specific generalised symptoms such as nausea, vomiting and headache. Myotoxicity (11) and anticoagulant coagulopathy (10) occurred frequently; haemolysis was seen in fewer cases (3). Two patients developed local tissue injury around the bite site requiring further treatment.

CONCLUSIONS

This study confirms previous reports about P. australis bites with respect to high rates of envenoming, commonly associated with pain and swelling and systemic effects of rhabdomyolysis and anticoagulant coagulopathy. Systemic envenoming, even severe cases, responds well to antivenom therapy. Compared to other Australian snakes, a high proportion of bites occur in people asleep at night. Medically significant local tissue injury around the bite site may occur and may be associated with inappropriate first-aid, particularly the vascular occlusive type.

Snakebite in Australia: a practical approach to diagnosis and treatment

Snakebite is a potential medical emergency and must receive high-priority assessment and treatment, even in patients who initially appear well. Patients should be treated in hospitals with onsite laboratory facilities, appropriate antivenom stocks and a clinician capable of treating complications such as anaphylaxis. All patients with suspected snakebite should be admitted to a suitable clinical unit, such as an emergency short-stay unit, for at least 12 hours after the bite. Serial blood testing (activated partial thromboplastin time, international normalised ratio and creatine kinase level) and neurological examinations should be done for all patients. Most snakebites will not result in significant envenoming and do not require antivenom. Antivenom should be administered as soon as there is evidence of envenoming. Evidence of systemic envenoming includes venom-induced consumption coagulopathy, sudden collapse, myotoxicity, neurotoxicity, thrombotic microangiopathy and renal impairment. Venomous snake groups each cause a characteristic clinical syndrome, which can be used in combination with local geographical distribution information to determine the probable snake involved and appropriate antivenom to use. The Snake Venom Detection Kit may assist in regions where the range of possible snakes is too broad to allow the use of monovalent antivenoms. When the snake identification remains unclear, two monovalent antivenoms (eg, brown snake and tiger snake antivenom) that cover possible snakes, or a polyvalent antivenom, can be used. One vial of the relevant antivenom is sufficient to bind all circulating venom. However, recovery may be delayed as many clinical and laboratory effects of venom are not immediately reversible. For expert advice on envenoming, contact the National Poisons Information Centre on 13 11 26.

Mulga snake (Pseudechis australis) envenoming: a spectrum of myotoxicity, anticoagulant coagulopathy, haemolysis and the role of early antivenom therapy - Australian Snakebite Project (ASP-19)

CONTEXT

Mulga snakes (Pseudechis australis) are venomous snakes with a wide distribution in Australia. Objective. The objective of this study was to describe mulga snake envenoming and the response of envenoming to antivenom therapy.

MATERIALS AND METHODS

Definite mulga bites, based on expert identification or venom-specific enzyme immunoassay, were recruited from the Australian Snakebite Project. Demographics, information about the bite, clinical effects, laboratory investigations and antivenom treatment are recorded for all patients. Blood samples are collected to measure the serum venom concentrations pre- and post-antivenom therapy using enzyme immunoassay.

RESULTS

There were 17 patients with definite mulga snake bites. The median age was 37 years (6-70 years); 16 were male and six were snake handlers. Thirteen patients had systemic envenoming with non-specific systemic symptoms (11), anticoagulant coagulopathy (10), myotoxicity (7) and haemolysis (6). Antivenom was given to ten patients; the median dose was one vial (range, one-three vials). Three patients had systemic hypersensitivity reactions post-antivenom. Antivenom reversed the coagulopathy in all cases. Antivenom appeared to prevent myotoxicity in three patients with high venom concentrations, given antivenom within 2 h of the bite. Median peak venom concentration in 12 envenomed patients with samples was 29 ng/mL (range, 0.6-624 ng/mL). There was a good correlation between venom concentrations and the area under the curve of the creatine kinase for patients receiving antivenom after 2 h. Higher venom concentrations were also associated with coagulopathy and haemolysis. Venom was not detected after antivenom administration except in one patient who had a venom concentration of 8.3 ng/ml after one vial of antivenom, but immediate reversal of the coagulopathy.

DISCUSSION

Mulga snake envenoming is characterised by myotoxicity, anticoagulant coagulopathy and haemolysis, and has a spectrum of toxicity that is venom dose dependant. This study supports a dose of one vial of antivenom, given as soon as a systemic envenoming is identified, rather than waiting for the development of myotoxicity.

Clinical effects and antivenom dosing in brown snake (Pseudonaja spp.) envenoming--Australian snakebite project (ASP-14)

Background

Snakebite is a global health issue and treatment with antivenom continues to be problematic. Brown snakes (genus Pseudonaja) are the most medically important group of Australian snakes and there is controversy over the dose of brown snake antivenom. We aimed to investigate the clinical and laboratory features of definite brown snake (Pseudonaja spp.) envenoming, and determine the dose of antivenom required.

Methods and Finding

This was a prospective observational study of definite brown snake envenoming from the Australian Snakebite Project (ASP) based on snake identification or specific enzyme immunoassay for Pseudonaja venom. From January 2004 to January 2012 there were 149 definite brown snake bites [median age 42y (2–81y); 100 males]. Systemic envenoming occurred in 136 (88%) cases. All envenomed patients developed venom induced consumption coagulopathy (VICC), with complete VICC in 109 (80%) and partial VICC in 27 (20%). Systemic symptoms occurred in 61 (45%) and mild neurotoxicity in 2 (1%). Myotoxicity did not occur. Severe envenoming occurred in 51 patients (38%) and was characterised by collapse or hypotension (37), thrombotic microangiopathy (15), major haemorrhage (5), cardiac arrest (7) and death (6). The median peak venom concentration in 118 envenomed patients was 1.6 ng/mL (Range: 0.15–210 ng/mL). The median initial antivenom dose was 2 vials (Range: 1–40) in 128 patients receiving antivenom. There was no difference in INR recovery or clinical outcome between patients receiving one or more than one vial of antivenom. Free venom was not detected in 112/115 patients post-antivenom with only low concentrations (0.4 to 0.9 ng/ml) in three patients.

Conclusions

Envenoming by brown snakes causes VICC and over a third of patients had serious complications including major haemorrhage, collapse and microangiopathy. The results of this study support accumulating evidence that giving more than one vial of antivenom is unnecessary in brown snake envenoming.

In vitro neurotoxic effects of Pseudechis spp. venoms: A comparison of avian and murine skeletal muscle preparations

Two common in vitro skeletal muscle preparations used for the study of venom neurotoxicity are the indirectly stimulated chick isolated biventer cervicis nerve-muscle preparation and the rat isolated phrenic nerve-diaphragm preparation. The aim of the current study was to compare the in vitro neurotoxicity of six Pseudechis spp. (Black snakes) venoms in both avian (chicken) and mammalian (rat) skeletal muscle preparations to determine differences in sensitivity. All Pseudechis spp. venoms significantly inhibited indirect twitches, in both preparations, indicating the presence of post synaptic neurotoxins. The inhibitory effects of all venoms were more rapid in the avian preparation, except for Pseudechis colletti venom where no significant difference was seen between the murine and avian muscles. Time taken to produce 50% reduction in stimulated twitches (i.e. t(50)) was markedly shorter in the avian preparation. We have shown that the avian in vitro preparation is more sensitive to the neurotoxic activity of Pseudechis spp. than the murine preparation. This difference is likely to be due to species differences in the interaction between the neurotoxins and the nicotinic receptor binding sites as well as differences in the 'safety factor' between the preparations.

Death adder envenoming causes neurotoxicity not reversed by antivenom--Australian Snakebite Project (ASP-16)

BACKGROUND

Death adders (Acanthophis spp) are found in Australia, Papua New Guinea and parts of eastern Indonesia. This study aimed to investigate the clinical syndrome of death adder envenoming and response to antivenom treatment.

METHODOLOGY/PRINCIPAL FINDINGS

Definite death adder bites were recruited from the Australian Snakebite Project (ASP) as defined by expert identification or detection of death adder venom in blood. Clinical effects and laboratory results were collected prospectively, including the time course of neurotoxicity and response to treatment. Enzyme immunoassay was used to measure venom concentrations. Twenty nine patients had definite death adder bites; median age 45 yr (5-74 yr); 25 were male. Envenoming occurred in 14 patients. Two further patients had allergic reactions without envenoming, both snake handlers with previous death adder bites. Of 14 envenomed patients, 12 developed neurotoxicity characterised by ptosis (12), diplopia (9), bulbar weakness (7), intercostal muscle weakness (2) and limb weakness (2). Intubation and mechanical ventilation were required for two patients for 17 and 83 hours. The median time to onset of neurotoxicity was 4 hours (0.5-15.5 hr). One patient bitten by a northern death adder developed myotoxicity and one patient only developed systemic symptoms without neurotoxicity. No patient developed venom induced consumption coagulopathy. Antivenom was administered to 13 patients, all receiving one vial initially. The median time for resolution of neurotoxicity post-antivenom was 21 hours (5-168). The median peak venom concentration in 13 envenomed patients with blood samples was 22 ng/mL (4.4-245 ng/mL). In eight patients where post-antivenom bloods were available, no venom was detected after one vial of antivenom.

CONCLUSIONS/SIGNIFICANCE

Death adder envenoming is characterised by neurotoxicity, which is mild in most cases. One vial of death adder antivenom was sufficient to bind all circulating venom. The persistent neurological effects despite antivenom, suggests that neurotoxicity is not reversed by antivenom.

Procoagulant adaptation of a blood coagulation prothrombinase-like enzyme complex in australian elapid venom

The macromolecular enzyme complex prothrombinase serves an indispensable role in blood coagulation as it catalyzes the conversion of prothrombin to thrombin, a key regulatory enzyme in the formation of a blood clot. Interestingly, a virtually identical enzyme complex is found in the venom of some Australian elapid snakes, which is composed of a cofactor factor Va-component and a serine protease factor Xa-like subunit. This review will provide an overview of the identification and characterization of the venom prothrombinase complex and will discuss the rationale for its powerful procoagulant nature responsible for the potent hemostatic toxicity of the elapid venom.

Cross-neutralisation of Australian brown snake, taipan and death adder venoms by monovalent antibodies

An understanding of the cross-neutralisation of snake venoms by antibodies is important for snake antivenom development. We investigated the cross-neutralisation of brown snake (Pseudonaja textilis) venom, taipan (Oxyuranus scutellatus) venom and death adder (Acanthophis antarcticus) with commercial antivenoms and monovalent anti-snake IgG, using enzyme immunoassays, in vitro clotting and neurotoxicity assays. Each commercial antivenom bound all three venoms, and neutralised clotting activity of brown snake and taipan venoms and neurotoxicity of death adder venom. The 'in-house' monovalent anti-snake venom IgG raised against procoagulant brown snake and taipan venoms, did not neutralise the neurotoxic effects of death adder venom. However, they did cross-neutralise the procoagulant effects of both procoagulant venoms. This supports the idea of developing antivenoms against groups of snake toxins rather than individual snake venoms.

Investigating pressure bandaging for snakebite in a simulated setting: bandage type, training and the effect of transport

BACKGROUND

The clinical evidence base for the use of pressure bandaging in snakebite is limited. We aimed to investigate if pressure bandages (PB) generated and maintained presumptive optimal pressures in a simulated setting.

METHODS

A total of 96 subjects were recruited, 78 health professionals and 18 from the general public. Participants were asked to apply PB with crepe and with an elasticized bandage without instruction. A paediatric blood pressure cuff attached to a pressure transducer was used to measure the pressure generated. PB application with elasticized bandages was repeated by 36 participants (18 general public and 18 health professionals) with feedback on pressures attained, and reassessment on the sixth subsequent attempt. Pressure was also measured under correctly applied bandages during an ambulance ride.

RESULTS

The median pressure generated under crepe bandages was 28 mmHg (interquartile range [IQR]: 17-42 mmHg) compared with 47 mmHg (IQR 26-83 mmHg) with elasticized bandages, with most subgroups applying the elasticized bandage closer to the estimated optimal pressure (55-70 mmHg). Following training, the median pressure for the 36 participants was 65 mmHg (IQR 56-71 mmHg), closer to the optimal range than initial attempts. On initial bandaging, 5/36 (14%) participants achieved optimal pressure range with elasticized bandages, compared with 18/36 (50%) after training (P = 0.002). Crepe bandages initially correctly applied did not maintain desired pressure during ambulance transport on urban roads over 30 min. Elasticized bandages maintained pressure.

CONCLUSIONS

PB was poorly done by the general public and health professionals. Crepe bandages rarely generated optimal pressures compared with elasticized bandages, but training did improve participants' ability to apply elasticized bandages. PB recommendations should be modified to specify appropriate bandage types.

Human anti-snake venom IgG antibodies in a previously bitten snake-handler, but no protection against local envenoming

We report a 60 year old male bitten by snakes from the Acanthophis genus (Death adder) on two occasions who developed high titres of human IgG antibodies to Acanthophis venom detected at the time of the second bite. The patient was bitten by Acanthophis antarcticus (common death adder) on the first occasion, developed non-specific systemic effects and did not receive antivenom. Three months later he was bitten by Acanthophis praelongus (northern death adder) and he developed significant local myotoxicity associated with a moderate rise in the creatine kinase (maximum 4770 U/L). He was given antivenom 55 h after the bite and recovered over several days. Death adder venom was detected in serum at the time of the first bite, but not the second bite. Human IgG antibodies to death adder were detected on the second admission but not the first. However, despite the presence of antibodies to death adder venom and free venom not being detected, the patient still developed significant local myotoxicity.

A turbidimetric assay for the measurement of clotting times of procoagulant venoms in plasma

INTRODUCTION

Assessment of the procoagulant effect of snake venoms is important for understanding their effects. The aim of this study was to develop a simple automated method to measure clotting times to assess procoagulant venoms.

METHODS

A turbidimetric assay was developed which monitors changes in optical density when plasma and venom are mixed. Plasma was added simultaneously to venom solutions in a 96 well microtitre plate. After mixing, the optical density at 340 nm was monitored in a microplate reader every 30 s over 30 min. The clotting time was defined as the lag time until the absorbance sharply increased. The turbidimetric method was compared to manual measurement of the clotting time defined as the time when a strand of fibrin can be drawn out of the mixture. The two methods were done simultaneously, with the same venom and plasma, and compared by plotting the manual versus turbidimetric clotting times. Within-day and between-day runs were done and the coefficient of variation (CV) was calculated.

RESULTS

Plots comparing manual clotting times to the lag time in the turbidimetric assay showed good correlation between the two methods for brown snake (Pseudonaja textilis) venom, including 24 determinations in triplicate over six days for seven different venom concentrations. Good correlation was also found for four other venoms: tiger snake (Notechis scutatus), Carpet viper (Echis carinatus), Russell's viper (Daboia russelii) and Malaysian pit piper (Calloselasma rhodostoma). Between-day CV was in the range 10-20% for both methods, while within-day CV <10%.

DISCUSSION

The turbidimetric assay appears to be a simple and convenient automated method for the measurement of clotting times to assess the effects of procoagulant venoms.

Effectiveness of pressure-immobilization first aid for snakebite requires further study

In the prospective Royal Darwin Hospital snakebite study, pressure-immobilization first aid (PI) was used more often than in previous studies. However, bandages were not uncommonly too loose or not applied to the whole limb and immobilization was often neglected. While PI should continue to be promoted as the standard for Australia for the present, prospective multicentre studies of snakebite with quantitative assays for blood venom concentration will hopefully better elucidate the real effectiveness of PI and define the limitations of timing of application and determine the optimum types of bandage materials to use and the pressure required to be maintained.

Toxicologic information resources for reptile envenomations

The United States is the largest importer of reptiles in the world, with an estimated 1.5 to 2.0 million households keeping one or more reptiles. Snakes account for about 11% of these imports and it has been estimated that as many as 9% of these reptiles are venomous. Envenomations by nonindigenous venomous species are a rare but often serious medical emergency. Bites may occur during the care and handling of legitimate collections found in universities, zoos, or museums. The other predominant source of exotic envenomation is from amateur collectors participating in importation, propagation, and trade of non-native species. This article provides toxicologic information resources for snake envenomations.

Thrombotic microangiopathy from Australian brown snake (Pseudonaja) envenoming

BACKGROUND

Australian brown snake (genus Pseudonaja) envenoming causes a venom-induced consumptive coagulopathy (VICC). A proportion of cases go on to develop thrombotic microangiopathy characterized by thrombocytopenia, microangiopathic haemolytic anaemia (MAHA) and acute renal failure (ARF).

AIM

The aim of the study was to define better the natural history and empirical treatments for thrombotic microangiopathy in brown snake envenoming.

METHODS

A review of brown snake bites recruited to the Australian Snakebite Project (ASP), a national multicentre study of snake envenoming was undertaken. Serial data are recorded on clinical effects and laboratory results, including measurement of venom concentrations. We describe cases of thrombotic microangiopathy and compare these to cases without thrombotic microangiopathy.

RESULTS

From 32 cases of brown snake envenoming with severe VICC, four (13%) developed thrombotic microangiopathy, we also included two cases of thrombotic microangiopathy from prior to ASP. All six developed severe thrombocytopenia (<20 x 10(-9)/L), worst 3 days after the bite and resolving over a week, MAHA with fragmented red blood cells on the blood film and five developed anuric ARF requiring dialysis and lasting 2-8 weeks. All six received antivenom, which was delayed compared with other brown snake-envenoming cases. Four were treated with plasmapheresis. The severity and recovery of the thrombocytopenia, anaemia and renal function were similar with and without plasmapheresis. The median length of stay for MAHA cases was 14 days (interquartile range (IQR) 12-14) compared to 1.8 days (IQR 1.3-2) for all other cases.

CONCLUSION

Thrombotic microangiopathy resulting from brown snake bite appears to have a good prognosis and management should focus on early antivenom therapy and supportive care including dialysis. The role of plasmapheresis is yet to be defined.

Diversity of Toxic Components from the Venom of the Evolutionarily Distinct Black Whip Snake, Demansia vestigiata

Included among the more than 300 species of elapid snakes worldwide is the Australian genus Demansia, or whip snakes. Despite evidence to suggest adverse clinical outcomes from envenomation by these snakes, together with confusion on their true phylogenetic relationship to other Australian elapids, not a single toxin sequence has previously been reported from the venom of a Demansia species. We describe here a combined proteomic and transcriptomic approach characterizing the venom from the black whip snake, Demansia vestigiata. A total of 13 distinct toxin families were identified, including homologues of all of the major toxic components previously reported from the venom of other Australian elapids, such as factor X-like prothrombin activators, neurotoxins, phospholipases, cysteine rich secretory proteins, textilinin-like molecules, nerve growth factors, l-amino acid oxidases, vespryns, 5' nucleotidases, metalloproteinases, and C-type lectins as well as a novel dipeptidyl peptidase family. Phylogenetic analysis of these sequences revealed an early evolutionary split of the black whip snake from all other characterized Australian snakes, with a low degree of sequence identity between D. vestigiata and the other snakes, across all toxin families. The results of this study have important implications not only for the further characterization of venom from whip snakes, but also for our understanding of the evolutionary relationship of Australian snake species.

Efficacy of antivenom against the procoagulant effect of Australian brown snake (Pseudonaja sp.) venom: In vivo and in vitro studies

Snake venom induced consumption coagulopathy (VICC) is a common complication of snake bite due to prothrombin activators or thrombin-like enzymes in the venom. This study aimed to determine the efficacy and dose of antivenom for treating VICC in patients envenomed by brown snakes (Pseudonaja spp.), including in vitro coagulation studies. In serial blood samples from patients with brown snake envenoming, venom and antivenom concentrations were measured using enzyme immunoassays. In vitro mixtures of brown snake venom and antivenom were used to investigate antivenom binding, neutralisation of prothrombin activity, prevention of venom-mediated clotting and effect on thrombin generation parameters using a thrombinoscope. In 27 envenomed patients the median venom concentration was 20 ng/mL (Interquartile range[IQR]:12-44 ng/mL) prior to antivenom and was not detected after antivenom administration, including 9 patients given one vial. In vitro, 200 microg/mL of antivenom bound all free venom at venom concentrations seen in patients. In vitro prothrombinase activity of the venom (using a chromogenic substrate) was not neutralised by antivenom. However, for venom concentrations seen in humans, 100 microg/mL of antivenom prevented venom clotting activity in human plasma and 479 microg/mL neutralised procoagulant venom activity measured by triggering thrombin generation. One vial of antivenom appears to be sufficient to bind and neutralise all venom in patients with severe brown snake envenoming.

Spotted black snake (Pseudechis guttatus) envenoming

We report two cases of spotted black snake (Pseudechis guttatus) envenoming. One patient experienced localised burning pain around the bite and developed nausea, vomiting, diarrhoea, upper abdominal cramping and diaphoresis. He was treated with intravenous fluids and antiemetics, but no antivenom, and was discharged 23 hours after the bite. The second patient developed a severe headache, blurred vision and mild nausea, associated with severe pain and swelling of the bitten limb that took 4 days to resolve. No antivenom was given and the patient had no sequelae. Neither patient developed significant coagulopathy, myolysis or neuromuscular paralysis. Bites by this species appear to cause effects similar to those of the more common red-bellied black snake (P. porphyriacus).

Treatment of snakebite in Australia: the current evidence base and questions requiring collaborative multicentre prospective studies

Despite the wealth of anecdotes and case reports there are fundamental questions of management of snakebite in Australia that remain unresolved or for which the current evidence is limited. The efficacy in the field, potential limitations and possibility of improvements in pressure immobilisation first aid need objective studies in humans. Optimal bandage sizes, stretch and pressure for different sized limbs need further evaluation, as does the use of pressure pads. Better definitions of specific clinical envenoming syndromes attributable to individual snake species are required, including elucidation of within-genus variations, similarities and differences. Venom studies suggest this is especially important for species within the brown snake (Pseudonaja) and death adder (Acanthophis) genera. Appropriate antivenom types, doses and dosing intervals for individual snake species should be more formally studied in patients. Especially important are confirmation of the need for higher doses of brown snake antivenom, while possibly limiting unnecessarily high doses, confirmation of the critical importance of early antivenom use to prevent pre-synaptic neurotoxicity in Taipan and tiger snake bites and ascertainment of whether larger doses of antivenom are unhelpful in Taipan bites after specified time delays. Confirmation of clinical efficacy and dosing recommendations for use of tiger snake (Notechis) antivenom in envenoming from Australian copperhead (Austrelaps spp.), broad headed (Hoplocephalus spp.) and rough-scaled snakes (Tropidechis carinatus) also require formal study in patients. Other examples of clinical relevance of cross-specificity of current and future monospecific antivenoms and whether there are geographical variations in antivenom responses within species will require elucidation. Prospective multicentre collaborative studies with predefined data collection and serial venom level assays are proposed as the way forward in Australia to help resolve therapeutic uncertainties and to establish a firmer evidence base for best-practice treatment guidelines for Australasian elapid snakebite.

Enzyme immunoassays in brown snake (Pseudonaja spp.) envenoming: Detecting venom, antivenom and venom–antivenom complexes

Although a commercial snake venom detection kit (SVDK) is available to distinguish between the five major snake groups in Australia, there is no assay for quantifying venom or antivenom concentrations in envenomed patients. Serum samples were obtained from patients with brown snake (Pseudonaja spp.) envenoming before and after the administration of antivenom and patients with suspected brown snake bites but no evidence of envenoming. Enzyme immunoassays (EIAs) were developed for free venom, free antivenom and the venom-antivenom complex. Standard samples measured in duplicate had a coefficient of variation of less than 10%. The EIA for venom was able to detect brown snake venom down to concentrations of 3 ng/mL. A high baseline absorbance was measured in some patients that did not change with the addition of excess antivenom to the samples. In these patients, the baseline absorbance was subtracted from all measurements to calculate the true venom concentration. The EIA for brown snake antivenom had a limit of detection of 20 microg/mL, but 50 microg/mL was used as a cut-off based on assays in patients who had not received antivenom. The EIA for venom-antivenom complexes was unable to detect these at the low venom concentrations that occurred in patients. Quantification of venom and antivenom will help to determine the dose of antivenom required to bind venom and to establish appropriate end points for antivenom treatment.

IN VITRO NEUROTOXIC AND MYOTOXIC EFFECTS OF THE VENOM FROM THE BLACK WHIP SNAKE (DEMANSIA PAPUENSIS)

1. Black whip snakes belong to the family elapidae and are found throughout the northern coastal region of Australia. The black whip snake (Demansia papuensis) is considered to be potentially dangerous due to its size and phylogenetic distinctiveness. Previous liquid chromatography-mass spectrometry analysis of D. papuensis venom indicated a number of components within the molecular mass ranges compatible with neurotoxins. For the first time, this study examines the in vitro neurotoxic and myotoxic effects of the venom from D. papuensis. 2. Venom (10 microg/mL) caused significant inhibition of twitches elicited by stimulation (0.2 ms, 0.1 Hz, supramaximal V) of motor nerves in the chick biventer cervicis nerve-muscle preparation. This neurotoxic effect, which was postsynaptic in origin, was weak in comparison to that of most other Australian elapids. Prior addition (10 min) of polyvalent (PSAV) or tiger snake (TSAV) antivenom (5 units/mL) prevented venom-induced twitch inhibition. Addition of PSAV (5 units/mL) at t(50) failed to reverse the inhibitory effect but prevented further inhibition of nerve-mediated twitches. 3. The venom (20-50 microg/mL) is also myotoxic as indicated by a slowly developing contracture and inhibition of twitches elicited by direct stimulation (2 ms, 0.1 Hz, supramaximal V, in the presence of tubocurarine 10 micromol/L) of the chick biventer muscle. This activity was confirmed by histological examination of the muscle. 4. Fractionation and characterization of venom components is required to further investigate the reasons for the weak neurotoxic activity of D. papuensis venom.

Collett's snake (Pseudechis colletti) envenoming in snake handlers

BACKGROUND

Collett's snake (Pseudechis colletti) is a member of the black snake genus and occurs in a warm temperate to sub-tropical region of central Queensland, Australia. There are no reports of bites occurring in the wild, and bites were previously thought to cause only minor effects. They are a popular snake among zoos and exotic snake keepers.

AIM

To investigate the clinical effects of severe envenoming by Collett's snake, and possible treatment options.

DESIGN

Case series.

METHODS

Clinical and laboratory features are described for six bites, all in snake handlers.

RESULTS

All six bites were from captive snakes, resulting in severe envenoming in four. Two patients were treated early with black snake antivenom, and only developed an anticoagulant coagulopathy and mild myolysis. Two developed anticoagulant coagulopathy and severe rhabdomyolysis associated with acute renal failure, requiring haemodialysis; both received antivenom >10 h after the bite, and initially received minimal fluid replacement. Other effects included thrombocytopenia, non-immune haemolytic anaemia and a marked leukocytosis.

DISCUSSION

Collett's snake envenoming is characterized by early generalized systemic effects (nausea, vomiting, abdominal pain, diarrhoea and headache) and an anticoagulant coagulopathy, followed in some cases by rhabdomyolysis and acute renal failure in untreated patients within 24 h. Early initiation of fluid therapy and treatment with black snake antivenom should be undertaken in all envenomed patients.