Bites in Australian snake handlers--Australian snakebite project (ASP-15)

BACKGROUND

Snakebites in snake handlers are an important clinical problem that may differ to bites in the general population.

AIM

To investigate the epidemiology and clinical presentation of bites in snake handlers.

DESIGN

Prospective observational study.

METHODS

Bites in snake handlers recruited as part of the Australian Snakebite Project (ASP) from 2004 to 2011 were included in the study. Data were extracted from the ASP database, which included demographic and clinical information, laboratory tests and antivenom treatment.

RESULTS

From 1089 snake bites recruited to ASP, there were 106 (9.7%) bites in snake handlers. The median age was 40 years (range: 16-81 years) and 104 (98%) were males. The commonest circumstances of the bites were handling snakes (47), catching snakes (22), feeding snakes (18) and cleaning cages (11). Bites were to the upper limb in 103 cases. Bites were most commonly by Red-bellied black snakes (20), Brown snakes (17), Taipan (15), Tiger snakes (14) and Death adders (14). Envenoming occurred in 77 patients: venom-induced consumption coagulopathy in 45 patients (58%), neurotoxicity in 10 (13%) and myotoxicity in 13 (17%). Systemic hypersensitivity reactions (SHSRs) to venom occurred in eight, satisfying clinical criteria for anaphylaxis in five, of which three were hypotensive. Antivenom was administered in 60 envenomed patients. SHSRs to antivenom occurred in 15 (25%; 95% CI:15-38%), including 2 (3%:1-13%) with severe (hypotensive) reactions.

CONCLUSION

Bites in snake handlers remain a common, important problem involving a broad range of snakes. Neurotoxicity and myotoxicity are relatively common, consistent with the snakes involved. Venom anaphylaxis occured, despite previously being a poorly recognized problem in snake handlers. The incidence of SHSRs to antivenoms, including anaphylaxis, was not higher than that observed in non-snake handlers.

Tiger snake (Notechis spp) envenoming: Australian Snakebite Project (ASP-13)

OBJECTIVES

To describe the clinical syndrome associated with definite tiger snake (Notechis spp) envenoming and to examine the ability of tiger snake antivenom (TSAV) to bind free venom in vivo.

DESIGN, SETTING AND PARTICIPANTS

We conducted a prospective cohort study within the Australian Snakebite Project, reviewing all definite tiger snake envenoming cases between October 2004 and June 2011. Definite cases were identified by venom-specific enzyme immunoassay or expert snake identification.

MAIN OUTCOME MEASURES

Clinical effects of tiger snake envenoming; peak venom concentrations; number of vials of antivenom administered.

RESULTS

Fifty-six definite tiger snake envenomings were identified. Clinical effects included venom-induced consumption coagulopathy (VICC) (n = 53), systemic symptoms (n = 45), myotoxicity (n = 11) and neurotoxicity (n = 17). Thrombotic microangiopathy occurred in three patients, all of whom developed acute renal failure. There were no deaths. A bite-site snake venom detection kit test was done in 44 patients, but was positive for tiger snake in only 33 cases. Fifty-three patients received TSAV and eight of these patients had immediate hypersensitivity reactions, severe enough in one case to satisfy diagnostic criteria for severe anaphylaxis. The median peak venom concentration in 50 patients with pretreatment blood samples available was 3.2 ng/mL (interquartile range [IQR], 1-12 ng/mL; range 0.17-152 ng/mL). In 49 patients with post-treatment blood samples available, no venom was detected in serum after the first antivenom dose. Ten patients were given 1 vial of TSAV; the median dose was 2 vials (range, 1-4 vials). Pretreatment serum venom concentrations did not vary significantly between patients given 1 vial of TSAV and those given 2 or more vials.

CONCLUSION

Tiger snake envenoming causes VICC, systemic symptoms, neurotoxicity and myotoxicity. One vial of TSAV, the dose originally recommended when the antivenom was first made available, appears to be sufficient to bind all circulating venom.

A randomised controlled trial of two infusion rates to decrease reactions to antivenom

Background

Snake envenoming is a major clinical problem in Sri Lanka, with an estimated 40,000 bites annually. Antivenom is only available from India and there is a high rate of systemic hypersensitivity reactions. This study aimed to investigate whether the rate of infusion of antivenom reduced the frequency of severe systemic hypersensitivity reactions.

Methods and Findings

This was a randomized comparison trial of two infusion rates of antivenom for treatment of non-pregnant adult patients (>14 y) with snake envenoming in Sri Lanka. Snake identification was by patient or hospital examination of dead snakes when available and confirmed by enzyme-immunoassay for Russell’s viper envenoming. Patients were blindly allocated in a 11 randomisation schedule to receive antivenom either as a 20 minute infusion (rapid) or a two hour infusion (slow). The primary outcome was the proportion with severe systemic hypersensitivity reactions (grade 3 by Brown grading system) within 4 hours of commencement of antivenom. Secondary outcomes included the proportion with mild/moderate hypersensitivity reactions and repeat antivenom doses. Of 1004 patients with suspected snakebites, 247 patients received antivenom. 49 patients were excluded or not recruited leaving 104 patients allocated to the rapid antivenom infusion and 94 to the slow antivenom infusion. The median actual duration of antivenom infusion in the rapid group was 20 min (Interquartile range[IQR]:20–25 min) versus 120 min (IQR:75–120 min) in the slow group. There was no difference in severe systemic hypersensitivity reactions between those given rapid and slow infusions (32% vs. 35%; difference 3%; 95%CI:−10% to +17%;p = 0.65). The frequency of mild/moderate reactions was also similar. Similar numbers of patients in each arm received further doses of antivenom (30/104 vs. 23/94).

Conclusions

A slower infusion rate would not reduce the rate of severe systemic hypersensitivity reactions from current high rates. More effort should be put into developing better quality antivenoms.

Trial Registration

www.slctr.lk SLCTR/2007/005

Solving the 'Brown snake paradox': in vitro characterisation of Australasian snake presynaptic neurotoxin activity

Pseudonaja textilis (Eastern Brown snake) and Oxyuranus scutellatus scutellatus (Coastal taipan) are clinically important Australian elapid snakes, whose potent venoms contain the presynaptic (β) neurotoxins, textilotoxin and taipoxin, respectively, and a number of postsynaptic neurotoxins. However, while taipan envenoming frequently results in neurotoxicity, Brown snake envenoming causes an isolated coagulopathy and neurotoxicity is rare. This phenomenon is called the 'Brown snake paradox'. This study compared the pharmacology of both venoms and their respective presynaptic neurotoxins to investigate this phenomenon. From size-exclusion high performance liquid chromatography (HPLC) analysis textilotoxin represents a significantly smaller proportion (5.7%) of P. textilis venom compared to taipoxin in O. s. scutellatus venom (20.4%). In the chick biventer cervicis nerve-muscle (CBCNM) preparation both venoms caused concentration-dependent neurotoxicity, with P. textilis venom being significantly more potent than O. s. scutellatus venom. Conversely, taipoxin was significantly more potent than textilotoxin when compared at the same concentration. Textilotoxin only partially contributed to the overall neurotoxicity of P. textilis venom, while taipoxin accounted for the majority of the neurotoxicity of O. s. scutellatus venom in the CBCNM preparation. Compared with taipoxin, textilotoxin is less potent and constitutes a smaller proportion of the venom. This is likely to be the reason for the absence of neurotoxicity in envenomed humans thus explaining the 'Brown snake paradox'.

Clinical effects and treatment of envenoming by Hoplocephalus spp. snakes in Australia: Australian Snakebite Project (ASP-12)

There is limited information on envenoming by snakes of the genus Hoplocephalus from Eastern Australia. We investigated the clinical and laboratory features of patients with definite Hoplocephalus spp. bites including antivenom treatment, recruited to the Australian Snakebite Project. There were 15 definite Hoplocephalus spp. bites based on expert identification including eight by Hoplocephalus stephensi (Stephen's banded snakes), four by Hoplocephalus bungaroides (broad-headed snake) and three by H. bitorquatus (pale-headed snake). Envenoming occurred in 13 patients and was similar for the three species with venom induced consumption coagulopathy (VICC) in all envenomings. Seven patients had an INR >12 and partial VICC, with only incomplete fibrinogen consumption, occurred in three patients. Systemic symptoms occurred in eight patients. Myotoxicity and neurotoxicity did not occur. H. stephensi venom was detected in all three H. stephensi envenomings (1.1, 44 and 81 ng/mL) for whom pre-antivenom blood samples were available, and not detected in one without envenoming. In two cases with post-antivenom blood samples, venom was not detected after tiger snake antivenom (TSAV) was given. In vitro binding studies demonstrated that TSAV concentrations of 50mU/mL are sufficient to bind the majority of free H. stephensi venom components at concentrations above those detected in envenomed patients (100 ng/mL). Eleven patients received antivenom, median dose 2 vials (Range: 1 to 5 vials), which was TSAV in all but one case, where polyvalent antivenom was used. Immediate hypersensitivity reactions occurred in six cases including one case of anaphylaxis. Envenoming by Hoplocephalus spp. causes VICC and systemic symptoms, making it clinically similar to brown snake (Pseudonaja spp.) envenoming. Based on in vitro studies reported here, patients may be treated with one vial of TSAV, although one vial of brown snake antivenom may also be sufficient.

Low-dose adrenaline, promethazine, and hydrocortisone in the prevention of acute adverse reactions to antivenom following snakebite: a randomised, double-blind, placebo-controlled trial

BACKGROUND

Envenoming from snakebites is most effectively treated by antivenom. However, the antivenom available in South Asian countries commonly causes acute allergic reactions, anaphylactic reactions being particularly serious. We investigated whether adrenaline, promethazine, and hydrocortisone prevent such reactions in secondary referral hospitals in Sri Lanka by conducting a randomised, double-blind placebo-controlled trial.

METHODS AND FINDINGS

In total, 1,007 patients were randomized, using a 2 × 2 × 2 factorial design, in a double-blind, placebo-controlled trial of adrenaline (0.25 ml of a 1∶1,000 solution subcutaneously), promethazine (25 mg intravenously), and hydrocortisone (200 mg intravenously), each alone and in all possible combinations. The interventions, or matching placebo, were given immediately before infusion of antivenom. Patients were monitored for mild, moderate, or severe adverse reactions for at least 96 h. The prespecified primary end point was the effect of the interventions on the incidence of severe reactions up to and including 48 h after antivenom administration. In total, 752 (75%) patients had acute reactions to antivenom: 9% mild, 48% moderate, and 43% severe; 89% of the reactions occurred within 1 h; and 40% of all patients were given rescue medication (adrenaline, promethazine, and hydrocortisone) during the first hour. Compared with placebo, adrenaline significantly reduced severe reactions to antivenom by 43% (95% CI 25-67) at 1 h and by 38% (95% CI 26-49) up to and including 48 h after antivenom administration; hydrocortisone and promethazine did not. Adding hydrocortisone negated the benefit of adrenaline.

CONCLUSIONS

Pretreatment with low-dose adrenaline was safe and reduced the risk of acute severe reactions to snake antivenom. This may be of particular importance in countries where adverse reactions to antivenom are common, although the need to improve the quality of available antivenom cannot be overemphasized.

Factor deficiencies in venom-induced consumption coagulopathy resulting from Australian elapid envenomation: Australian Snakebite Project (ASP-10)

BACKGROUND

Limited information exists on the dynamics of hemostasis in patients with venom-induced consumption coagulopathy (VICC) from snake envenomation.

OBJECTIVE

The aim of the present study was to investigate specific factor deficiencies and their time course in Australasian elapid envenomation.

METHODS

We measured coagulation parameters and factor concentrations in patients recruited to the Australian Snakebite Project, an observational cohort study. There were 112 patients with complete VICC, defined as an international normalized ratio (INR) > 3, and 18 with partial VICC. Serial citrated plasma samples were collected from 0.5 to 60 h post-bite. INR, activated partial thromboplastin time (aPTT), coagulation factors (F)I, II, V, VII, VIII, IX, X, von Willebrand factor antigen (VWF:Ag) and D-dimer concentrations were measured.

RESULTS

Complete VICC was characterized by near/total depletion of fibrinogen, FV and FVIII, with an INR and aPTT that exceeded the upper limits of detection, within 2 h of snakebite. Prothrombin levels never fell below 60% of normal, suggesting that the toxins were rapidly eliminated or inactivated and re-synthesis of clotting factors occurred irrespective of antivenom. Partial VICC caused limited depletion of fibrinogen and FV, and almost complete consumption of FVIII. Onset of VICC was more rapid with brown snake (Pseudonaja spp.) venom, which contains a group C prothrombin activator toxin, compared with the tiger snake group, which contains a group D prothrombin activator toxin and requires human FVa formation. Resolution of VICC occurred within 24-36 h irrespective of snake type.

CONCLUSIONS

These results suggest that Australasian elapid prothrombin activators have a potent but short duration of action. Antivenom is unlikely to be administered in time to prevent VICC.

Changes in serial laboratory test results in snakebite patients: when can we safely exclude envenoming?

OBJECTIVES

To determine which laboratory tests are first associated with severe envenoming after a snakebite, when (ie, how long after the bite) the test results become abnormal, and whether this can determine a safe observation period after suspected snakebite.

DESIGN, PATIENTS AND SETTING

Prospective cohort study of 478 patients with suspected or confirmed snakebite recruited to the Australian Snakebite Project from January 2002 to April 2009, who had at least three sets of laboratory test results and at least 12 hours of observation in hospital after the bite. Severe envenoming was defined as venom-induced consumption coagulopathy (VICC), myotoxicity, neurotoxicity or thrombotic microangiopathy.

MAIN OUTCOME MEASURES

International normalised ratio (INR), activated partial thromboplastin time (aPTT), creatine kinase (CK) level, and neurological examination.

RESULTS

There were 240 patients with severe envenoming, 75 with minor envenoming and 163 non-envenomed patients. Of 206 patients with VICC, 178 had an INR > 1.2 (abnormal) on admission, and the remaining 28 had an INR > 1.2 within 12 hours of the bite. Of 33 patients with myotoxicity, a combination of CK > 250 U/L and an abnormal aPTT identified all but two cases by 12 hours; one of these two was identified within 12 hours by leukocytosis. Nine cases of isolated neurotoxicity had a median time of onset after the bite of 4 hours (range, 35 min - 12 h). The combination of serial INR, aPTT and CK tests and repeated neurological examination identified 213 of 222 severe envenoming cases (96%) by 6 hours and 238 of 240 (99%) by 12 hours.

CONCLUSION

Laboratory parameters (INR, aPTT and CK) and neurological reassessments identified nearly all severe envenoming cases within 12 hours of the bite, even in this conservative analysis that assumed normal test results if the test was not done.

Endogenous thrombin potential as a novel method for the characterization of procoagulant snake venoms and the efficacy of antivenom

Venom-induced consumption coagulopathy occurs in snake envenoming worldwide but the interaction between procoagulant snake venoms and human coagulation remains poorly understood. We aimed to evaluate an assay using endogenous thrombin potential (ETP) to investigate the procoagulant properties of a range of Australian whole venoms in human plasma and compared this to traditional clotting and prothrombinase activity studies. We developed a novel modification of ETP using procoagulant snake venoms to trigger thrombin production. This was used to characterise the relative potency, calcium and clotting factor requirements of five important Australian snake venoms and efficacy of commercial antivenom, and compared this to prothrombinase activity and clotting assays. All five venoms initiated thrombin generation in the absence and presence of calcium. Pseudonaja textilis (Brown snake; p<0.0001), Hoplocephalus stephensii (Stephen's-banded snake; p<0.0001) and Notechis scutatus (tiger snake; p=0.0073) all had statistically significant increases in ETP with calcium. Venom potency varied between assays, with ETP ranging from least potent with Oxyuranus scutellatus (Taipan) venom to intermediate with N. scutatus and H. stephensii venoms to most potent with P. textilis and Tropidechis carinatus (Rough-scale snake) venoms. ETPs for N. scutatus, T. carinatus and H. stephensii venoms were severely reduced with factor V deficient plasma. Antivenom neutralized the thrombin generating capacity but not prothrombin substrate cleaving ability of the venoms. Contrary to previous studies using clotting tests and factor Xa substrates, these venoms differ in calcium requirement. ETP is a useful assay to investigate mechanisms of other procoagulant venoms and is a robust method of assessing antivenom efficacy.

Development of a sensitive enzyme immunoassay for measuring taipan venom in serum

The detection and measurement of snake venom in blood is important for confirming snake identification, determining when sufficient antivenom has been given, detecting recurrence of envenoming, and in forensic investigation. Venom enzyme immunoassays (EIA) have had persistent problems with poor sensitivity and high background absorbance leading to false positive results. This is particularly problematic with Australasian snakes where small amounts of highly potent venom are injected, resulting in low concentrations being associated with severe clinical effects. We aimed to develop a venom EIA with a limit of detection (LoD) sufficient to accurately distinguish mild envenoming from background absorbance at picogram concentrations of venom in blood. Serum samples were obtained from patients with taipan bites (Oxyuranus spp.) before and after antivenom, and from rats given known venom doses. A sandwich EIA was developed using biotinylated rabbit anti-snake venom antibodies for detection. For low venom concentrations (i.e. <1 ng/mL) the assay was done before and after addition of antivenom to the sample (antivenom difference method). The LoD was 0.15 ng/mL for the standard assay and 0.1 ng/mL for the antivenom difference method. In 11 pre-antivenom samples the median venom concentration was 10 ng/mL (Range: 0.3-3212 ng/mL). In four patients with incomplete venom-induced consumption coagulopathy the median venom concentration was 2.4 ng/mL compared to 30 ng/mL in seven patients with complete venom-induced consumption coagulopathy. No venom was detected in any post-antivenom sample and the median antivenom dose prior to this first post-antivenom sample was 1.5 vials (1-3 vials), including 7 patients administered only 1 vial. In rats the assay distinguished a 3-fold difference in venom dose administered and there was small inter-individual variability. There was small but measurable cross-reactivity with black snake (Pseudechis), tiger snake (Notechis) and rough-scale snake (Tropidechis carinatus) venoms with the assay for low venom concentrations (<1 ng/mL). The use of biotinylation and the antivenom difference method in venom EIA produces a highly sensitive assay that will be useful for determining antivenom dose, forensic and clinical diagnosis.

Sensationalistic journalism and tales of snakebite: are rattlesnakes rapidly evolving more toxic venom?

Recent reports in the lay press have suggested that bites by rattlesnakes in the last several years have been more severe than those in the past. The explanation, often citing physicians, is that rattlesnakes are evolving more toxic venom, perhaps in response to anthropogenic causes. We suggest that other explanations are more parsimonious, including factors dependent on the snake and factors associated with the bite victim's response to envenomation. Although bites could become more severe from an increased proportion of bites from larger or more provoked snakes (ie, more venom injected), the venom itself evolves much too slowly to explain the severe symptoms occasionally seen. Increased snakebite severity could also result from a number of demographic changes in the victim profile, including age and body size, behavior toward the snake (provocation), anatomical site of bite, clothing, and general health including asthma prevalence and sensitivity to foreign antigens. Clinical management of bites also changes perpetually, rendering comparisons of snakebite severity over time tenuous. Clearly, careful study taking into consideration many factors will be essential to document temporal changes in snakebite severity or venom toxicity. Presently, no published evidence for these changes exists. The sensationalistic coverage of these atypical bites and accompanying speculation is highly misleading and can produce many detrimental results, such as inappropriate fear of the outdoors and snakes, and distraction from proven snakebite management needs, including a consistent supply of antivenom, adequate health care, and training. We urge healthcare providers to avoid propagating misinformation about snakes and snakebites.

Snake bite

Snake bite is a common and frequently devastating environmental and occupational disease, especially in rural areas of tropical developing countries. Its public health importance has been largely ignored by medical science. Snake venoms are rich in protein and peptide toxins that have specificity for a wide range of tissue receptors, making them clinically challenging and scientifically fascinating, especially for drug design. Although the full burden of human suffering attributable to snake bite remains obscure, hundreds of thousands of people are known to be envenomed and tens of thousands are killed or maimed by snakes every year. Preventive efforts should be aimed towards education of affected communities to use proper footwear and to reduce the risk of contact with snakes to a minimum through understanding of snakes' behaviour. To treat envenoming, the production and clinical use of antivenom must be improved. Increased collaboration between clinicians, epidemiologists, and laboratory toxinologists should enhance the understanding and treatment of envenoming.

Antivenom efficacy or effectiveness: the Australian experience

Despite widespread use of antivenoms, many questions remain about their effectiveness in the clinical setting. The almost universal acceptance of their value is based mainly on in vitro studies, animal studies and human observational studies. Numerous examples exist where they demonstrate clear benefit, such as consumption coagulopathy in viper envenoming, prevention of neurotoxicity in Australasian elapid bites, systemic effects in scorpion and funnel-web spider envenoming. There are also concerns about the quality and efficacy of some antivenoms. However, it is important not to confuse the efficacy of antivenom, defined as its ability to bind and neutralise venom-mediated effects under ideal conditions, and the effectiveness of antivenom, defined as its ability to reverse or prevent envenoming in human cases. There are numerous potential reasons for antivenom failure in human envenoming, of which antivenom inefficacy is only one. Other important reasons include venom-mediated effects being irreversible, antivenom being unable to reach the site of toxin-mediated injury, or the rapidity of onset of venom-mediated effects. A number of recent studies in Australia bring into question the effectiveness of some antivenoms, including snake antivenom for coagulopathy, redback spider and box jellyfish antivenoms. Despite brown snake antivenom being able to neutralise venom induced clotting in vitro, use of the antivenom in human envenoming does not appear to change the time course of coagulopathy. However, it is important that apparent antivenom ineffectiveness in specific cases is correctly interpreted and does not lead to a universal belief that antivenom is ineffective. It should rather encourage further studies to investigate the underlying pathophysiology of envenoming, the pharmacokinetics of venoms and antivenoms, and ultimately the effectiveness of antivenom based on snake type, clinical effects and timing of administration.

Failure of antivenom to improve recovery in Australian snakebite coagulopathy

BACKGROUND

Venom-induced consumption coagulopathy (VICC) is an important feature of snake envenoming.

AIM

To investigate the effect of antivenom and fresh frozen plasma (FFP) on recovery of VICC in Australian elapid snake envenoming.

DESIGN

Prospective cohort study.

METHODS

Patients with VICC were included from the Australian Snakebite Project (ASP). Time to recovery of VICC (defined as time until INR <2) was investigated using a time to event analysis in WinBUGS. The model considered the effects of age, sex, snake type, time of antivenom after bite, antivenom dose and use of FFP within 4 h.

RESULTS

The study included 167 cases of VICC, median age being 41 [interquartile range (IQR): 28-53) years, and 130 (78%) were males. Antivenom was administered at a median of 3.6 (IQR: 2.2-5.6) h after the bite at a median dose of four vials (IQR: 2-6 vials). Thirteen patients received FFP within 4 h. Recovery of VICC occurred after a median of 14.4 (IQR: 11.5-17.5) h, and only the use of FFP within 4 h influenced the time to recovery. Neither antivenom dose nor time of antivenom administration had an effect on recovery of VICC. In patients administered with FFP, 12% [credible interval (CrI): 6-21%] and 81% (CrI: 61-94%) had recovered at 6 and 12 h, respectively, vs 2.5% (CrI: 1.5-4%) and 28% (CrI: 22-34%) not receiving FFP.

DISCUSSION

Antivenom did not appear to be effective for the coagulopathy in snake envenoming in Australia. FFP appeared to shorten the time of VICC recovery.

The global snakebite crisis--a public health issue misunderstood, not neglected

The global problem of venomous snakebite continues to attract attention despite it being described as a "neglected" issue. The current focus of the World Health Organization (WHO) remains anti-snake venom quality, although "availability and sustainability" of supply are consistently described as the key issues. Sustainability of antivenom supply has been elusive, with cost and pricing in developing countries being cited as the major reasons. The current WHO approach fails to explore the cost issue, but rather focuses on quality improvements, which may well adversely affect the costs of a product already perceived to be 'unaffordable.' The reference to cost and price indicates a marketing-based perspective may well give more relevant solutions to the snakebite crisis. This paper introduces a marketing model to examine global snakebite and to identify if the current approach is relevant and effective. The "4 Ps" model examines if the correct products are available, whether sufficient information exists concerning estimated market size, whether the assumptions frequently made about the costs of the product are correct and fully understood, if the product is promoted properly, and whether the method by which the product reaches the end user is optimum. The resulting analysis demonstrates that the current approach is characterized by a misunderstanding of the nature of the global snakebite problem. Further, a lack of implementation of key solutions, such as training doctors in developing countries with relevant protocols, has inevitably led to a lack of improvement in the snakebite arena over the last 30 years.