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

A randomized controlled trial and prospective cohort investigating antivenom for red-bellied black snake envenomation

INTRODUCTION

Antivenom is first line treatment for snake envenomation worldwide, despite few placebo controlled clinical trials demonstrating effectiveness. We aimed to investigate whether early antivenom in red-bellied black snake (Pseudechis porphyriacus) bites would prevent systemic myotoxicity.

METHODS

We undertook a multicentre randomized placebo-controlled trial of antivenom for red-bellied black snake bites with patients recruited from the Australian Snakebite Project (July 2014 to June 2020). In addition, we report all patients with red-bellied black snake bites during the same period, comparing the same outcomes. Patients over 2 years of age with definite red-bellied black snake bites and early systemic effects were randomized to receive 50 per cent glucose (placebo) or tiger snake antivenom within 6 hours post-bite, or in the cohort group received antivenom determined by the treating clinician. The primary outcome was the proportion of patients with myotoxicity (peak creatine kinase activity >1,000 U/L). Secondary outcomes were: area under the curve of total creatine kinase elevation over 48 hours, presence of venom post-antivenom, and adverse reactions. We analyzed both the randomized control trial patients and the combination of randomized control trial and cohort patients.

RESULTS

Fifteen patients were recruited to the randomized controlled trial, and a cohort of 68 patients who were not randomized were included in the analysis. After treatment, two of seven patients given placebo had a peak creatine kinase activity >1,000 U/L versus none of the eight given antivenom (difference in favour of antivenom; 29 per cent; 95 per cent confidence interval:-18 per cent to +70 per cent; P = 0.2). The median area under the curve of total creatine kinase elevation over 48 hours in patients given placebo was 0 U/L*h (interquartile range: 0-124 U/L*h), which was not significantly different to those given antivenom: 197 U/L*h (interquartile range: 0-66,353 U/L*h; P = 0.26). Venom was not detected post-antivenom in six patients with measured venom concentrations given antivenom. Two patients given antivenom had immediate hypersensitivity reactions, one severe anaphylaxis, and another had serum sickness. Combining randomized and not randomized patients, three of 36 (8 per cent) administered antivenom less than 6 hours post-bite had a peak creatine kinase activity >1,000 U/L versus 17/47 (36 per cent) patients not receiving antivenom less than 6 hours post-bite (difference in favour of antivenom 29 per cent; 95 per cent confidence interval: 8 per cent to 44 per cent; P < 0.004). Overall, 13/36 (36 per cent) patients administered antivenom within 6 hours had hypersensitivity reactions, six severe anaphylaxis (17 per cent).

DISCUSSION

We found that early antivenom was effective in red-bellied black snake bites, and only three patients need to be given antivenom within 6 hours to prevent myotoxicity in one (number needed to treat = 3). However, one in three patients administered antivenom developed a hypersensitivity reaction, and one in six had severe anaphylaxis. The major limitation of this study was the small number of patients recruited to the randomized controlled trial.

CONCLUSION

Administration of antivenom in red-bellied black snake envenomation within 6 hours post-bite appeared to decrease the proportion of patients with myotoxicity, but a third of patients had adverse reactions.

Bites by Non-Native Reptiles in France: Species, Circumstances and Outcome

We aimed to make an exhaustive assessment of circumstances of bites by exotic reptiles bred in France. A retrospective observational study was conducted in all the reported cases from 2000 to 2020 in French poison control centers (PCCs). Two hundred and eighteen cases of bites were recorded. The sex ratio (M/F) of the patients was 1.79 and the mean age of the patients was 29.0 ± 15.8 years. Twenty-two cases (10.1%) occurred during the deep night. One hundred and eighty-six bites (85.7%) occurred in a private context; however, there were more cases of high severity when it occurred in a professional setting (60.0% vs. 11.2%, p < 0.01). The feeding/nursing activity accounted for 54.7% cases. Forty-three species of snake were identified; 28 were considered venomous. There were no deaths among the patients in the study. Most of the cases (85.8%) were of mild severity. All of the patients bitten by a venomous reptile were hospitalized: 10 patients received an antivenom; and 2 required surgery. Bites occurred at home and by a small number of popular non-venomous reptile species (pythons and boas, colubrids). These occurred mainly when handling the animals. The rare envenomations were mainly by Asian and American crotalids, followed by elapids. One-third of them were treated with antivenom when available.

Fangs for the Memories? A Survey of Pain in Snakebite Patients Does Not Support a Strong Role for Defense in the Evolution of Snake Venom Composition

Animals use venoms for multiple purposes, most prominently for prey acquisition and self-defense. In snakes, venom composition often evolves as a result of selection for optimization for local diet. However, whether selection for a defensive function has also played a role in driving the evolution of venom composition has remained largely unstudied. Here, we use an online survey of snakebite victims to test a key prediction of a defensive function, that envenoming should result in the rapid onset of severe pain. From the analysis of 584 snakebite reports, involving 192 species of venomous snake, we find that the vast majority of bites do not result in severe early pain. Phylogenetic comparative analysis shows that where early pain after a bite evolves, it is often lost rapidly. Our results, therefore, do not support the hypothesis that natural selection for antipredator defense played an important role in the origin of venom or front-fanged delivery systems in general, although there may be intriguing exceptions to this rule.

Antivenom for Neuromuscular Paralysis Resulting From Snake Envenoming

Antivenom therapy is currently the standard practice for treating neuromuscular dysfunction in snake envenoming. We reviewed the clinical and experimental evidence-base for the efficacy and effectiveness of antivenom in snakebite neurotoxicity. The main site of snake neurotoxins is the neuromuscular junction, and the majority are either: (1) pre-synaptic neurotoxins irreversibly damaging the presynaptic terminal; or (2) post-synaptic neurotoxins that bind to the nicotinic acetylcholine receptor. Pre-clinical tests of antivenom efficacy for neurotoxicity include rodent lethality tests, which are problematic, and in vitro pharmacological tests such as nerve-muscle preparation studies, that appear to provide more clinically meaningful information. We searched MEDLINE (from 1946) and EMBASE (from 1947) until March 2017 for clinical studies. The search yielded no randomised placebo-controlled trials of antivenom for neuromuscular dysfunction. There were several randomised and non-randomised comparative trials that compared two or more doses of the same or different antivenom, and numerous cohort studies and case reports. The majority of studies available had deficiencies including poor case definition, poor study design, small sample size or no objective measures of paralysis. A number of studies demonstrated the efficacy of antivenom in human envenoming by clearing circulating venom. Studies of snakes with primarily pre-synaptic neurotoxins, such as kraits (Bungarus spp.) and taipans (Oxyuranus spp.) suggest that antivenom does not reverse established neurotoxicity, but early administration may be associated with decreased severity or prevent neurotoxicity. Small studies of snakes with mainly post-synaptic neurotoxins, including some cobra species (Naja spp.), provide preliminary evidence that neurotoxicity may be reversed with antivenom, but placebo controlled studies with objective outcome measures are required to confirm this.

Incidence of serum sickness after the administration of Australian snake antivenom (ASP-22)

CONTEXT

Serum sickness is a delayed immune reaction resulting from the injection of foreign protein or serum. Antivenom is known to cause serum sickness but the incidence and characteristics are poorly defined.

OBJECTIVE

To investigate the incidence and clinical features of serum sickness following the administration of Australian snake antivenoms.

MATERIALS AND METHODS

This was a prospective cohort study of patients recruited to the Australian Snakebite Project who received snake antivenom from November 2012 to March 2014. Demographics, clinical information, laboratory tests and antivenom treatment were recorded prospectively. Patients administered antivenom were followed up at 7-10 days and 6 weeks' post-antivenom. The primary outcome was the proportion with serum sickness, pre-defined as three or more of: fever, erythematous rash/urticaria, myalgia/arthralgia, headache, malaise, nausea/vomiting 5-20 days post-antivenom.

RESULTS

During the 16-month period, 138 patients received antivenom. 23 were not followed up (unable to contact, tourist, child, bee sting) and 6 died in hospital. Of 109 patients followed up, the commonest reason for antivenom was venom induced consumption coagulopathy in 77 patients. An acute systemic hypersensitivity reaction occurred post-antivenom in 25 (23%) and 8 (7%) were severe with hypotension. Serum sickness occurred in 32/109 (29%) patients, including 15/37 (41%) given tiger snake, 6/15 (40%) given polyvalent and 4/23 (17%) given brown snake antivenom. There was no association between the volume of antivenom and serum sickness, p = 0.18. The commonest effects were lethargy, headache, muscle/joint aches and fever.

DISCUSSION

The incidence of serum sickness after snake antivenom in Australia was higher than earlier investigations which failed to define symptoms or follow-up patients, but similar to more recent studies of antivenoms in the United States.

CONCLUSION

Serum sickness is common with Australian snake antivenom but does not appear to be predictable based on the volume of antivenom administered.

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.

Immune response to snake envenoming and treatment with antivenom; complement activation, cytokine production and mast cell degranulation

Background

Snake bite is one of the most neglected public health issues in poor rural communities worldwide. In addition to the clinical effects of envenoming, treatment with antivenom frequently causes serious adverse reactions, including hypersensitivity reactions (including anaphylaxis) and pyrogenic reactions. We aimed to investigate the immune responses to Sri Lankan snake envenoming (predominantly by Russell's viper) and antivenom treatment.

Methodology/Principal Findings

Plasma concentrations of Interleukin (IL)-6, IL-10, tumor necrosis factor α (TNFα), soluble TNF receptor I (sTNFRI), anaphylatoxins (C3a, C4a, C5a; markers of complement activation), mast cell tryptase (MCT), and histamine were measured in 120 Sri Lankan snakebite victims, both before and after treatment with antivenom. Immune mediator concentrations were correlated with envenoming features and the severity of antivenom-induced reactions including anaphylaxis. Envenoming was associated with complement activation and increased cytokine concentrations prior to antivenom administration, which correlated with non-specific systemic symptoms of envenoming but not with coagulopathy or neurotoxicity. Typical hypersensitivity reactions to antivenom occurred in 77/120 patients (64%), satisfying criteria for a diagnosis of anaphylaxis in 57/120 (48%). Pyrogenic reactions were observed in 32/120 patients (27%). All patients had further elevations in cytokine concentrations, but not complement activation, after the administration of antivenom, whether a reaction was noted to occur or not. Patients with anaphylaxis had significantly elevated concentrations of MCT and histamine.

Conclusions/Significance

We have demonstrated that Sri Lankan snake envenoming is characterized by significant complement activation and release of inflammatory mediators. Antivenom treatment further enhances the release of inflammatory mediators in all patients, with anaphylactic reactions characterised by high levels of mast cell degranulation but not further complement activation. Anaphylaxis is probably triggered by non allergen-specific activation of mast cells and may be related to the quality of available antivenom preparations, as well as a priming effect from the immune response to the venom itself.

Snakebites cause life-threatening symptoms including uncontrolled bleeding and paralysis. The body's immune responses to snake venom may contribute to the severity of these symptoms but have not been well characterized in humans. Treatment with antivenom is potentially lifesaving, but also carries risk, as severe allergic reactions (anaphylaxis) are common. Anaphylaxis occurs when mast cells, triggered by either allergen-specific antibodies, other immunological mechanisms, or non-immune mechanisms, release mediators that cause skin rashes, shortness of breath and, in severe cases, life-threatening hypotension and/or hypoxia. We have studied 120 snakebite victims in Sri Lanka, both before and after treatment with antivenom. Our results have shown snakebite triggers activation of the complement cascade (an important part of the body's innate immune defence) and production of proinflammatory mediators. In addition, we have demonstrated a quite astonishing level of immune activation after antivenom treatment in virtually every person treated, regardless of whether they had a reaction to the antivenom. Half of the patients treated experienced anaphylaxis, with clear evidence of mast cell activation. Anaphylaxis to antivenom is unlikely to be triggered by allergen-specific antibodies, as patients had not been previously exposed to antivenom, but may be related to the quality of available antivenom preparations, as well as a priming effect from the immune response to the venom itself.