Randomised controlled double-blind non-inferiority trial of two antivenoms for saw-scaled or carpet viper (Echis ocellatus) envenoming in Nigeria

Neurotoxic snakebites in Africa: Clinical implications, therapeutic strategies, and antivenom efficacy

Snakebite is a significant health concern in Africa, particularly due to neurotoxic envenomation which can lead to neuromuscular paralysis and respiratory failure. In Nigeria, snakes from the Elapidae family are a notable cause of envenomation cases, though these incidents are underreported. This review examined case reports of neurotoxic envenomation in Africa, highlighting the clinical impacts and the efficacy of available antivenoms. Preclinical studies showed that the polyvalent antivenom from the South African Institute for Medical Research (SAIMR) was highly effective against neurotoxicity with a protective efficacy (R) of 1346.80 mg/mL, while clinical assessment emphasized the need for high-dose antivenom therapy along with supportive measures like mechanical ventilation. Unlike hemorrhagic envenomation, where antivenom promptly resolves bleeding, neurotoxic cases often require additional interventions. The review underscores the necessity for tailored approaches in antivenom therapy to address the complexities of neurotoxic snakebites and reduce their public health burden in Africa.

Improving in vivo assays in snake venom and antivenom research: A community discussion

On the 26 th January 2023, a free to attend, 'improving in vivo snake venom research: a community discussion' meeting was held virtually. This webinar brought together researchers from around the world to discuss current neutralisation of venom lethality mouse assays that are used globally to assess the efficacy of therapies for snakebite envenoming. The assay's strengths and weaknesses were highlighted, and we discussed what improvements could be made to refine and reduce animal testing, whilst supporting preclinical antivenom and drug discovery for snakebite envenoming. This report summarises the issues highlighted, the discussions held, with additional commentary on key perspectives provided by the authors.

Synthetic development of a broadly neutralizing antibody against snake venom long-chain α-neurotoxins

Snakebite envenoming is a major global public health concern for which improved therapies are urgently needed. The antigenic diversity present in snake venom toxins from various species presents a considerable challenge to the development of a universal antivenom. Here, we used a synthetic human antibody library to find and develop an antibody that neutralizes long-chain three-finger α-neurotoxins produced by numerous medically relevant snakes. Our antibody bound diverse toxin variants with high affinity, blocked toxin binding to the nicotinic acetylcholine receptor in vitro, and protected mice from lethal venom challenge. Structural analysis of the antibody-toxin complex revealed a binding mode that mimics the receptor-toxin interaction. The overall workflow presented is generalizable for the development of antibodies that target conserved epitopes among antigenically diverse targets, and it offers a promising framework for the creation of a monoclonal antibody-based universal antivenom to treat snakebite envenoming.

A prospective observational phase IV study on effectiveness of animal derived polyclonal antibody antivenoms against West African carpet viper (Echis romani) induced coagulopathy and mortality

Conventional polyclonal antibody antivenoms are the mainstay of snakebite therapy. They have not been proven to be efficacious in randomized placebo controlled clinical trials among severely envenomed patients. There is also paucity of evidence on effectiveness especially in routine use. The current study evaluated their effectiveness in post marketing use among those managed with and without antivenom as regards to reversal of venom induced coagulopathy defined using the 20 min Whole Blood Clotting Test [20WBCT] and in averting death. The effectiveness of antivenom was evaluated among 5467 patients predominantly envenomed by the West African carpet viper (Echis romani) at 3 hospitals in Nigeria from 2021 to 2022. Two antivenoms Echitab G (EG) and Echitab ICP Plus (EP) were able to restore normal clotting within 6 h of administration in 58.0% [95% Confidence Interval (95%CI)] (95%CI:51.2-64.5%) and 91.7% (95%CI:90.4-93.0%) of patients respectively. They were able to restore normal clotting within 24 h of administration in 96.9% (95%CI:94.0-98.7%) and 99.0% (95%CI:98.4-99.4%) of patients respectively. The Odds Ratio [OR (95%CI)] of dying among patients with positive 20WBCT who were treated with ≥1 vial of either EG or EP compared to those not treated was 0.06 (0.02-0.23) and 0.07 (0.03-0.15) respectively. This equated to antivenom protection against in-hospital mortality of 93-94% among patients with confirmed coagulopathy though the benefit appeared abrogated among those without coagulopathy. The untreated natural mortality was 15.94% (95%CI:8.24-26.74%) without antivenom therapy while the overall mortality was 84/5105 (1.65%; 95%CI:1.32-2.03%. The Number Needed to Treat (NNT) to avert a death was 7 patients among patients with coagulopathy. Antivenoms were safe with mild early adverse reactions observed among 2.6% (95%CI:2.13-3.08%) of antivenom recipients. Polyclonal antibody antivenoms are effective and safe for treating coagulopathic envenomed patients in Nigeria.

Diagnostic characteristics of the 20-minute whole blood clotting test in detecting venom-induced consumptive coagulopathy following carpet viper envenoming

INTRODUCTION

Envenoming by Echis spp. (carpet or saw-scaled vipers) causes haemorrhage and coagulopathy and represents a significant proportion of snakebites in the savannah regions of West Africa. Early diagnosis of envenoming is crucial in the management of these patients and there is limited evidence on the utility of the 20-minute whole blood clotting test (20WBCT) in diagnosing venom-induced consumptive coagulopathy (VICC) following envenoming by Echis ocellatus.

METHODS

A prospective observational cohort study was conducted at the Kaltungo General Hospital in North-eastern Nigeria from September 2019 to September 2021. Standardised 20WBCTs were conducted by trained hospital staff and citrated plasma samples were collected at numerous timepoints. Prothrombin time (PT) and international normalised ratio (INR) were determined using a semi-automated analyser and INR values were calculated using international sensitivity indices (ISI). The sensitivity, specificity, positive predictive values (PPV), negative predictive values (NPV), and likelihood ratios of the 20WBCT compared to an INR ≥ 1.4 were calculated, alongside 95% confidence intervals.

RESULTS

We enrolled 121 patients into our study, with a median age of 26 (18.0-35.0) years and a male predominance (75.2%). The 20WBCT was positive (abnormal) in 101 out of 121 patients at timepoint 0h, of which 95 had an INR ≥ 1.4, giving a sensitivity of 87.2% (95%CI 79.4-92.8). Among patients with a negative 20WBCT (normal), six had an INR < 1.4 giving a specificity of 50% (95%CI 21.1-78.9%). The positive and negative likelihood ratios were 1.7 (95%CI 1.6-1.9) and 0.3 (95%CI 0.1-0.4) respectively.

CONCLUSION

The 20WBCT is a simple, cheap, and easily accessible bedside test with a high sensitivity for the detection of patients with venom induced consumptive coagulopathy (VICC) following envenoming by E. ocellatus, although false positives do occur. Repeated 20WBCTs can identify patients with new, persistent, and rebound coagulopathy.

Snake Antivenoms-Toward Better Understanding of the Administration Route

Envenomations induced by animal bites and stings constitute a significant public health burden. Even though a standardized protocol does not exist, parenterally administered polyclonal antivenoms remain the mainstay in snakebite therapy. There is a prevailing opinion that their application by the i.m. route has poor efficacy and that i.v. administration should preferentially be chosen in order to achieve better accomplishment of the antivenom therapeutic activity. Recently, it has been demonstrated that neutralization not only in the systemic circulation but also in the lymphatic system might be of great importance for the clinical outcome since it represents another relevant body compartment through which the absorption of the venom components occurs. In this review, the present-day and summarized knowledge of the laboratory and clinical findings on the i.v. and i.m. routes of antivenom administration is provided, with a special emphasis on the contribution of the lymphatic system to the process of venom elimination. Until now, antivenom-mediated neutralization has not yet been discussed in the context of the synergistic action of both blood and lymph. A current viewpoint might help to improve the comprehension of the venom/antivenom pharmacokinetics and the optimal approach for drug application. There is a great need for additional dependable, practical, well-designed studies, as well as more practice-related experience reports. As a result, opportunities for resolving long-standing disputes over choosing one therapeutic principle over another might be created, improving the safety and effectiveness of snakebite management.

Clinical aspects of snakebite envenoming and its treatment in low-resource settings

There is increasing recognition of the public health importance of snakebite envenoming. Worldwide annual incidence is likely to be 5 million bites, with mortality exceeding 150 000 deaths, and the resulting physical and psychological morbidity leads to substantial social and economic repercussions. Prevention through community education by trained health workers is the most effective and economically viable strategy for reducing risk of bites and envenoming. Clinical challenges to effective treatment are most substantial in rural areas of low-resource settings, where snakebites are most common. Classic skills of history taking, physical examination, and use of affordable point-of-care tests should be followed by monitoring of evolving local and systemic envenoming. Despite the profusion of new ideas for interventions, hyperimmune equine or ovine plasma-derived antivenoms remain the only specific treatment for snakebite envenoming. The enormous interspecies and intraspecies complexity and diversity of snake venoms, revealed by modern venomics, demands a radical redesign of many current antivenoms.

Performance of the 20 minutes Whole Blood Clotting Test in detection, monitoring and antivenom therapy of West African Carpet viper (Echis romani) envenoming in resource constrained settings in Nigeria

The 20 minutes Whole Blood Clotting Test (20WBCT) was evaluated in 1541 snakebite patients at 3 hospitals in Nigeria. It was useful in detection, monitoring, guiding antivenom therapy and prognostication of coagulopathy, with initial sensitivity of 84.7% (95%CI:82.7-86.5%) and specificity of 64.3% (95%CI:50.4-76.7%) compared to clinical envenoming. It led to correct decisions regarding administration or withholding antivenom in 97.93% of patients. The proportion of carpet viper (Echis romani) envenomed patients who restored clotting rose steadily following effective antivenom therapy. Patients with positive 20WBCT had severer envenoming, required more blood transfusion, had longer hospital stay and derived higher antivenom protection against death from carpet viper. However, there was no association between positive 20WBCT and fatality or complications.

Commercial Antivenoms Exert Broad Paraspecific Immunological Binding and In Vitro Inhibition of Medically Important Bothrops Pit Viper Venoms

Snakebite envenoming is a life threatening neglected tropical disease that represents a considerable public health concern in the tropics. Viperid snakes of the genus Bothrops are among those of greatest medical importance in Latin America, and they frequently cause severe systemic haemotoxicity and local tissue destructive effects in human victims. Although snakebite antivenoms can be effective therapeutics, their efficacy is undermined by venom toxin variation among snake species. In this study we investigated the extent of paraspecific venom cross-reactivity exhibited by three distinct anti-Bothrops antivenoms (Soro antibotrópico-crotálico, BothroFav and PoliVal-ICP) against seven different Bothrops pit viper venoms from across Latin America. We applied a range of in vitro assays to assess the immunological binding and recognition of venom toxins by the antivenoms and their inhibitory activities against specific venom functionalities. Our findings demonstrated that, despite some variations, the monovalent antivenom BothroFav and the polyvalent antivenoms Soro antibotrópico-crotálico and PoliVap-ICP exhibited extensive immunological recognition of the distinct toxins found in the different Bothrops venoms, with Soro antibotrópico-crotálico generally outperformed by the other two products. In vitro functional assays revealed outcomes largely consistent with the immunological binding data, with PoliVap-ICP and BothroFav exhibiting the greatest inhibitory potencies against procoagulant and fibrinogen-depleting venom activities, though Soro antibotrópico-crotálico exhibited potent inhibition of venom metalloproteinase activities. Overall, our findings demonstrate broad levels of antivenom paraspecificity, with in vitro immunological binding and functional inhibition often highly comparable between venoms used to manufacture the antivenoms and those from related species, even in the case of the monovalent antivenom BothroFav. Our findings suggest that the current clinical utility of these antivenoms could possibly be expanded to other parts of Latin America that currently suffer from a lack of specific snakebite therapies.

Exploring the Utility of ssDNA Aptamers Directed against Snake Venom Toxins as New Therapeutics for Snakebite Envenoming

Snakebite is a neglected tropical disease that causes considerable death and disability in the tropical world. Although snakebite can cause a variety of pathologies in victims, haemotoxic effects are particularly common and are typically characterised by haemorrhage and/or venom-induced consumption coagulopathy. Antivenoms are the mainstay therapy for treating the toxic effects of snakebite, but despite saving thousands of lives annually, these therapies are associated with limited cross-snake species efficacy due to venom variation, which ultimately restricts their therapeutic utility to particular geographical regions. In this study, we sought to explore the potential of ssDNA aptamers as toxin-specific inhibitory alternatives to antibodies. As a proof of principle model, we selected snake venom serine protease toxins, which are responsible for contributing to venom-induced coagulopathy following snakebite envenoming, as our target. Using SELEX technology, we selected ssDNA aptamers against recombinantly expressed versions of the fibrinogenolytic SVSPs ancrod from the venom of C. rhodostoma and batroxobin from B. atrox. From the resulting pool of specific ssDNA aptamers directed against each target, we identified candidates that exhibited low nanomolar binding affinities to their targets. Downstream aptamer-linked immobilised sorbent assay, fibrinogenolysis, and coagulation profiling experiments demonstrated that the candidate aptamers were able to recognise native and recombinant SVSP toxins and inhibit the toxin- and venom-induced prolongation of plasma clotting times and the consumption of fibrinogen, with inhibitory potencies highly comparable to commercial polyvalent antivenoms. Our findings demonstrate that rationally selected toxin-specific aptamers can exhibit broad in vitro cross-reactivity against toxin isoforms found in different snake venoms and are capable of inhibiting toxins in pathologically relevant in vitro and ex vivo models of venom activity. These data highlight the potential utility of ssDNA aptamers as novel toxin-inhibiting therapeutics of value for tackling snakebite envenoming.

Outcomes in intervention research on snakebite envenomation: a systematic review

INTRODUCTION

A core outcome set (COS) is a minimal list of consensus outcomes that should be used in all intervention research in a specific domain. COS enhance the ability to undertake meaningful comparisons and to understand the benefits or harms of different treatments. A first step in developing a COS is to identify outcomes that have been used previously. We did this global systematic review to provide the foundation for development of a region-specific COS for snakebite envenomation.  Methods: We searched 15 electronic databases, eight trial registries, and reference lists of included studies to identify reports of relevant trials, protocols, registry records and systematic reviews. We extracted verbatim data on outcomes, their definitions, measures, and time-points. Outcomes were classified as per an existing outcome taxonomy, and we identified unique outcomes based on similarities in the definition and measurement of the verbatim outcomes.

RESULTS

We included 107 records for 97 studies which met our inclusion criteria. These reported 538 outcomes, with a wide variety of outcome measures, definitions, and time points for measurement. We consolidated these into 88 unique outcomes, which we classified into core areas of mortality (1, 1.14 %), life impact (6, 6.82%), resource use (15, 17.05%), adverse events (7, 7.95%), physiological/clinical (51, 57.95%), and composite (8, 9.09%) outcomes. The types of outcomes varied by the type of intervention, and by geographic region. Only 15 of the 97 trials (17.04%) listed Patient Related Outcome Measures (PROMS).

CONCLUSION

Trials evaluating interventions for snakebite demonstrate heterogeneity on outcomes and often omit important information related to outcome measurement (definitions, instruments, and time points). Developing high quality, region-specific COS for snakebite could inform the design of future trials and improve outcome reporting. Measurement of PROMS, resource use and life impact outcomes in trials on snakebite remains a gap.

TRUE-1: Trial of Repurposed Unithiol for snakebite Envenoming phase 1 (safety, tolerability, pharmacokinetics and pharmacodynamics in healthy Kenyan adults)

Background: Snakebites affect over 5 million people each year, and over 100,000 per year die as a result. The only available treatment is antivenom, which has many shortcomings including high cost, intravenous administration, and high risk of adverse events. One of the most abundant and harmful components of viper venoms are the zinc-dependent snake venom metalloproteinases (SVMPs). Unithiol is a chelating agent which is routinely used to treat heavy metal poisoning. In vivo experiments in small animal models have demonstrated that unithiol can prevent local tissue damage and death caused by a certain viper species. This phase I clinical trial will assess the safety of ascending doses of unithiol with a view for repurposing for snakebite indication.

Methods: This open label, single agent, phase I clinical trial of a repurposed drug has a primary objective to evaluate the safety of escalating doses of unithiol, and a secondary objective to describe its pharmacokinetics. In total, 64 healthy Kenyan volunteers from Kilifi County will be dosed in consecutive groups of eight, with dose escalation decisions dependent on review of safety data by an independent data safety monitoring board. Four groups will receive ascending single oral doses, two will receive multiple oral doses, and two will receive single intravenous doses. Follow-up will be for 6-months and includes full adverse event reporting. Pharmacokinetic analysis will define the Cmax, Tmax, half-life and renal elimination.

Conclusions: This clinical trial will assess the safety and tolerability of a promising oral therapeutic in a relevant setting where snakebites are prevalent. Unithiol is likely to be safer than antivenom, is easier to manufacture, has activity against diverse snake species, and can be administered orally, and thus shows promise for repurposing for tropical snakebite.

Pan African Clinical Trials Registry: PACTR202103718625048 (3/3/2021)

Treatment outcomes among snakebite patients in north-west Ethiopia-A retrospective analysis

BACKGROUND

Millions of people are bitten by venomous snakes annually, causing high mortality and disability, but the true burden of this neglected health issue remains unknown. Since 2015, Médecins Sans Frontières has been treating snakebite patients in a field hospital in north-west Ethiopia. Due to the poor market situation for effective and safe antivenoms for Sub-Saharan Africa, preferred antivenom was not always available, forcing changes in choice of antivenom used. This study describes treatment outcomes and the effectiveness and safety of different antivenoms used.

METHODOLOGY / PRINCIPAL FINDINGS

This retrospective observational study included 781 snakebite patients presenting at the field hospital between 2015 and 2019. Adjusted odds ratios, 95%-CI and p-values were used to compare the treatment outcome of patients treated with Fav-Afrique (n = 149), VacSera (n = 164), and EchiTAb-PLUS-ICP (n = 156) antivenom, and to identify the risk of adverse reactions for each antivenom. Whereas only incidental snakebite cases presented before 2015, after treatment was made available, cases rapidly increased to 1,431 in 2019. Envenomation was mainly attributed to North East African saw-scaled viper (Echis pyramidum) and puff adder (Bitis arietans). Patients treated with VacSera antivenom showed lower chance of uncomplicated treatment outcome (74.4%) compared to Fav-Afrique (93.2%) and EchiTAb-PLUS-ICP (90.4%). VacSera and EchiTAb-PLUS-ICP were associated with 16- and 6-fold adjusted odds of treatment reaction compared to Fav-Afrique, respectively, and VacSera was weakly associated with higher odds of death.

CONCLUSIONS / SIGNIFICANCE

Snakebite frequency is grossly underreported unless treatment options are available. Although EchiTAb-PLUS-ICP showed favorable outcomes in this retrospective analysis, prospective randomized trials are needed to evaluate the effectiveness and safety of the most promising antivenoms for Sub-Saharan Africa. Structural investment in sustained production and supply of antivenom is urgently needed.

Antivenom: An immunotherapy for the treatment of snakebite envenoming in sub-Saharan Africa

Snakebite envenoming (SBE) leads to significant morbidity and mortality, resulting in over 90,000 deaths and approximately 400,000 amputations annually. In sub-Saharan Africa (SSA) alone, SBE accounts for over 30,000 deaths per annum. Since 2017, SBE has been classified as a priority Neglected Tropical Disease (NTD) by the World Health Organisation (WHO). The major species responsible for mortality from SBE within SSA are from the Bitis, Dendroaspis, Echis and Naja genera. Pharmacologically active toxins such as metalloproteinases, serine proteinases, 3-finger toxins, kunitz-type toxins, and phospholipase A₂s are the primary snake venom components. These toxins induce cytotoxicity, coagulopathy, hemorrhage, and neurotoxicity in envenomed victims. Antivenom is currently the only available venom-specific treatment for SBE and contains purified equine or ovine polyclonal antibodies, collected from donor animals repeatedly immunized with low doses of adjuvanted venom. The resulting plasma or serum contains a high titre of specific antibodies, which can then be collected and stored until required. The purified antibodies are either whole IgG, monovalent fragment antibody (Fab) or divalent fragment antibody F(ab')₂. Despite pharmacokinetic and pharmacodynamic differences, all three are effective in the treatment of SBE. No antivenom is without adverse reactions but, the level of their impact and severity varies from benign early adverse reactions to the rarely occurring fatal anaphylactic shock. However, the major side effects are largely reversible with immediate administration of adrenaline and corticosteroids. There are 16 different antivenoms marketed within SSA, but the efficacy and safety profiles are only published for less than 50% of these products.

Access to antivenoms in the developing world: A multidisciplinary analysis

Access to safe, effective, quality-assured antivenom products that are tailored to endemic venomous snake species is a crucial component of recent coordinated efforts to reduce the global burden of snakebite envenoming. Multiple access barriers may affect the journey of antivenoms from manufacturers to the bedsides of patients. Our review describes the antivenom ecosystem at different levels and identifies solutions to overcome these challenges. At the global level, there is insufficient manufacturing output to meet clinical needs, notably for antivenoms intended for use in regions with a scarcity of producers. At national level, variable funding and deficient regulation of certain antivenom markets can lead to the procurement of substandard antivenom. This is particularly true when producers fail to seek registration of their products in the countries where they should be used, or where weak assessment frameworks allow registration without local clinical evaluation. Out-of-pocket expenses by snakebite victims are often the main source of financing antivenoms, which results in the underuse or under-dosing of antivenoms, and a preference for low-cost products regardless of efficacy. In resource-constrained rural areas, where the majority of victims are bitten, supply of antivenom in peripheral health facilities is often unreliable. Misconceptions about treatment of snakebite envenoming are common, further reducing demand for antivenom and exacerbating delays in reaching facilities equipped for antivenom use. Multifaceted interventions are needed to improve antivenom access in resource-limited settings. Particular attention should be paid to the comprehensive list of actions proposed within the WHO Strategy for Prevention and Control of Snakebite Envenoming.

Immunorecognition capacity of Indian polyvalent antivenom against venom toxins from two populations of Echis carinatus

Clinicians report low efficacy of Indian polyvalent antivenom (PAV), with >20 vials required for treatment of a snakebite envenoming. We hypothesize that the antivenom efficacy could be reduced due to insufficient antibodies against some venom toxins. To test this, we used third-generation antivenomics to reveal bound and unbound venom toxins of Echis carinatus venom from Goa (ECVGO) and Tamil Nadu (ECVTN). We used 60, 120, 180, 240, 300, and 360 μg of venom and passed through mini-columns containing ~5 mg Antivenom bound to CNBr beads. The non-retained (unbound) and retained (bound) toxins were identified using reverse-phase HPLC and tandem mass spectrometry. Low molecular weight toxins - Short disintegrins (5.3 kDa) and DIS domain of P-II SVMP from ECVGO and ECVTN showed poor binding with antivenom. The immunorecognition sites of antivenom saturated at the lower antivenom-venom ratio for ECVGO than for ECVTN. The immunoretained capacity of antivenom against ECVTN was 140.6 μg and ECVGO was 125.1 μg. The amount of immunoretained toxins quantified can further be used to estimate the efficacy of antivenom by correlating it with in-vivo studies. The unbound toxins identified from this study could be targeted to improve the effectiveness of antivenom.

Livestock herding and Fulani ethnicity are a combined risk factor for development of early adverse reactions to antivenom treatment: Findings from a cross-sectional study in Nigeria

Background

Adverse reactions to antivenom considerably complicate the clinical management of snakebite envenomed patients because it necessitates a temporary suspension of life-saving antivenom, increases costs and can compromise patient outcomes. This study sought to explore the association between cattle-herding occupation and ethnic group and the occurrence of early adverse reactions to antivenom.

Methods

This cross-sectional study was conducted between the 25th April and 11th July 2011 at the Kaltungo General Hospital in north east Nigeria. The exposure variable of cattle-herding occupation showed a strong correlation with the ethnic group variable, thus these were combined into a new variable with three categories (Fulani and herder, either Fulani or herder, and neither Fulani nor herder). The outcome variable was the occurrence of early adverse reactions, defined as any new symptoms occurring within 6 hours of antivenom administration. Odds Ratios were estimated using multivariable logistic regression models controlling for potential confounders.

Results

Among 231 envenomed snakebite victims, the overall incidence of early adverse reactions was 11.9% (95% confidence intervals: 8.0–16.9%). Patients who were Fulani and herders had a higher incidence of early adverse reactions compared to patients who were neither Fulani nor herders (20% vs 5.7%). After adjusting for age and gender, victims who were Fulani and herders were 5.9 times more likely to have an early adverse reaction, compared to victims who were neither Fulani nor herders (95% CI: 1.88–18.59; p = 0.002).

Interpretation

To the best of our knowledge, this is the first study to provide evidence of higher odds of early adverse reactions among patients from a particular occupation and/or ethnic group. We recommend that snake envenomed patients of Fulani origin be especially closely monitored for adverse reactions, that hospitals receiving these patients be appropriately resourced to manage both envenoming and adverse reactions and that premedication with adrenaline should be considered. Our findings provide an argument for speculation on the influence of immunological or lifestyle-related differences on the occurrence of early adverse reactions to antivenom.

Antivenom is the first-choice treatment of systemic snake envenoming that annually affects between 1.8–2.7 million victims globally. Access to antivenom is especially poor for those in greatest need because they typically reside in impoverished, rural tropical communities dependent upon health facilities with limited resources. In addition, clinical treatment of snakebite victims is further complicated by early adverse reactions (EARs) to antivenom-treatment. The causes of antivenom-associated EARs are poorly understood and under-researched. Despite antivenom producers instituting costly remedial manufacturing steps (removal of pyrogens and other impurities) to make their products safer, EARs still affect a high proportion of antivenom-treated patients. Instigated by anecdotal observations to the corresponding author from clinicians in rural Nigerian hospitals that snakebite victims of cattle-herding occupation, and especially those of Fulani ethnicity, suffer more frequent EARs than other groups, this cross-sectional study identified that risks of developing EARs to antivenom treatment include the ethnicity and pastoral lifestyle of snakebite patients. To our knowledge, this is the first study to identify that EARs to antivenom-treatment include factors associated with the victim, as well as factors related to the antivenom itself. We emphasise the need for more research on the causes of adverse reactions to antivenom so that strategies to reduce incidence can be implemented.

Pathology-specific experimental antivenoms for haemotoxic snakebite: The impact of immunogen diversity on the in vitro cross-reactivity and in vivo neutralisation of geographically diverse snake venoms

BACKGROUND

Snakebite is a neglected tropical disease that causes high global rates of mortality and morbidity. Although snakebite can cause a variety of pathologies in victims, haemotoxic effects are particularly common and are typically characterised by haemorrhage and/or venom-induced consumption coagulopathy. Antivenoms are the mainstay therapeutic for treating the toxic effects of snakebite, but despite saving thousands of lives annually, these therapies are associated with limited cross-snake species efficacy due to venom variation, which ultimately restricts their therapeutic utility to particular geographical regions.

METHODOLOGY/PRINCIPAL FINDINGS

In this study we explored the feasibility of generating globally effective pathology-specific antivenoms to counteract the haemotoxic signs of snakebite envenoming. Two different immunogen mixtures, consisting of seven and twelve haemotoxic venoms sourced from geographically diverse and/or medically important snakes, were used to raise ovine polyclonal antibodies, prior to characterisation of their immunological binding characteristics and in vitro neutralisation profiles against each of the venoms. Despite variability of the immunogen mixtures, both experimental antivenoms exhibited broadly comparable in vitro venom binding and neutralisation profiles against the individual venom immunogens in immunological and functional assays. However, in vivo assessments using a murine preclinical model of antivenom efficacy revealed substantial differences in venom neutralisation. The experimental antivenom generated from the seven venom immunogen mixture outperformed the comparator, by providing protective effects against venom lethality caused by seven of the eight geographically diverse venoms tested, including three distinct venoms that were not used as immunogens to generate this antivenom. These findings suggest that a core set of venom immunogens may be sufficient to stimulate antibodies capable of broadly neutralising a geographically diverse array of haemotoxic snake venoms, and that adding additional venom immunogens may impact negatively on the dose efficacy of the resulting antivenom.

CONCLUSIONS/SIGNIFICANCE

Although selection of appropriate immunogens that encapsulate venom toxin diversity without diluting antivenom potency remains challenging and further optimisation is required, the findings from this pilot study suggest that the generation of pathology-specific antivenoms with global utility is likely to feasible, thereby highlighting their promise as future modular treatments for the world's tropical snakebite victims.

R, Geevar T, Zachariah A, Sharma SK, Bhatt N, Mukaka M, Harriss E, Lalloo DG, Ashley EA, Monteiro WM, Smithuis F, Eddleston M. The 20-minute whole blood clotting test (20WBCT) for snakebite coagulopathy-A systematic review and meta-analysis of diagnostic test accuracy

BACKGROUND

The 20-minute whole blood clotting test (20WBCT) has been used to detect coagulopathy following snakebite for almost 50 years. A systematic review and meta-analysis of the 20WBCT was conducted to evaluate the accuracy of the 20WBCT to detect coagulopathy, indicative of systemic envenoming.

METHODS AND FINDINGS

Databases were searched from inception up to 09/12/2020 to identify studies that compared the 20WBCT and INR/fibrinogen on five or more subjects. Data was extracted from full-text articles by two reviewers using a predetermined form. Authors of 29 studies that lacked sufficient details in the manuscript were contacted and included if data meeting the inclusion criteria were provided. Included studies were evaluated for bias using a tailored QUADAS-2 checklist. The study protocol was prospectively registered on PROSPERO database (CRD42020168953). The searches identified 3,599 studies, 15 met the inclusion criteria and 12 were included in the meta-analysis. Data was reported from 6 countries and included a total of 2,270 patients. The aggregate weighted sensitivity of the 20WBCT at detecting INR >1.4 was 0.84 (CI 0.61 to 0.94), the specificity was 0.91 (0.76 to 0.97) and the SROC AUC was 0.94 (CI 0.91 to 0.96). The aggregate weighted sensitivity of the 20WBCT at detecting fibrinogen <100 mg/dL was 0.72 (CI 0.58 to 0.83), the specificity was 0.94 (CI 0.88 to 0.98) and the SROC AUC was 0.93 (0.91 to 0.95). Both analyses that used INR and fibrinogen as the reference test displayed considerable heterogeneity.

CONCLUSIONS

In the absence of laboratory clotting assays, the 20WBCT remains a highly specific and fairly sensitive bedside test at detecting coagulopathy following snakebite. However, clinicians should be aware of the importance of operator training, standardized equipment and the lower sensitivity of the 20WBCT at detecting mild coagulopathy and resolution of coagulopathy following antivenom.

Clinical outcomes and outcome measurement tools reported in randomised controlled trials of treatment for snakebite envenoming: A systematic review

BACKGROUND

Snakebite is a priority neglected tropical disease and causes a range of complications that vary depending on the snake species. Randomised clinical trials have used varied outcome measures that do not allow results to be compared or combined. In accordance with the Core Outcomes Measurements in Effectiveness Trials (COMET) initiative, this systematic review aims to support the development of a globally relevant core outcome set for snakebite.

METHODS

All randomised controlled trials, secondary analyses of randomised controlled trials and study protocols investigating the efficacy of therapeutics for human snakebite envenoming were eligible for inclusion. Study screening and data extraction were conducted in duplicate by two independent reviewers. All primary and secondary outcome measures were extracted and compiled, as were adverse event outcome measures. Similar outcome measures were grouped into domains. The study was prospectively registered with PROSPERO: CRD42020196160.

RESULTS

This systematic review included 43 randomised controlled trials, two secondary analyses and 13 study protocols. A total of 382 outcome measures were extracted and, after duplicates were merged, there were 153 unique outcomes. The most frequently used outcome domain ('venom antigenaemia') was included in less than one third of the studies. The unique outcomes were classified into 60 outcome domains. Patient-centred outcomes were used in only three of the studies.

DISCUSSION

Significant heterogeneity in outcome measures exists in snakebite clinical trials. Consensus is needed to select outcome measures that are valid, reliable, patient-centred and feasible. The results of this systematic review strongly support the development of a core outcome set for use in snakebite clinical trials.

Snakebite envenoming in different national contexts: Costa Rica, Sri Lanka, and Nigeria

Snakebite envenoming is a neglected tropical disease that predominantly affects impoverished rural communities in sub-Saharan Africa, Asia, and Latin America. The global efforts to reduce the impact of this disease must consider the local national contexts and, therefore, comparative studies on envenomings in different countries are necessary to identify strengths, weaknesses and needs. This work presents a comparative analysis of snakebite envenomings in Costa Rica, Sri Lanka, and Nigeria. The comparison included the following aspects: (a) burden of envenomings, (b) historical background of national efforts to confront envenomings, (c) national health systems, (d) antivenom availability and accessibility including local production, (e) training of physicians and nurses in the diagnosis and management of envenomings, (f) prevention campaigns and community-based work, (g) scientific and technological platforms in these topics, and (h) international cooperation programs. Strengths and weaknesses were identified in the three contexts and several urgent tasks to improve the management of this disease in these countries are highlighted. This comparative analysis could be of benefit for similar studies in other national and regional contexts.

Preclinical validation of a repurposed metal chelator as an early-intervention therapeutic for hemotoxic snakebite

Snakebite envenoming causes 138,000 deaths annually, and ~400,000 victims are left with permanent disabilities. Envenoming by saw-scaled vipers (Viperidae: Echis) leads to systemic hemorrhage and coagulopathy and represents a major cause of snakebite mortality and morbidity in Africa and Asia. The only specific treatment for snakebite, antivenom, has poor specificity and low affordability and must be administered in clinical settings because of its intravenous delivery and high rates of adverse reactions. This requirement results in major treatment delays in resource-poor regions and substantially affects patient outcomes after envenoming. Here, we investigated the value of metal ion chelators as prehospital therapeutics for snakebite. Among the tested chelators, dimercaprol (British anti-Lewisite) and its derivative 2,3-dimercapto-1-propanesulfonic acid (DMPS) were found to potently antagonize the activity of Zn²⁺-dependent snake venom metalloproteinases in vitro. Moreover, DMPS prolonged or conferred complete survival in murine preclinical models of envenoming against a variety of saw-scaled viper venoms. DMPS also considerably extended survival in a "challenge and treat" model, where drug administration was delayed after venom injection and the oral administration of this chelator provided partial protection against envenoming. Last, the potential clinical scenario of early oral DMPS therapy combined with a delayed, intravenous dose of conventional antivenom provided prolonged protection against the lethal effects of envenoming in vivo. Our findings demonstrate that the safe and affordable repurposed metal chelator DMPS can effectively neutralize saw-scaled viper venoms in vitro and in vivo and highlight the promise of this drug as an early, prehospital, therapeutic intervention for hemotoxic snakebite envenoming.

Health and economic burden estimates of snakebite management upon health facilities in three regions of southern Burkina Faso

Background

Snakebite has become better recognized as a significant cause of death and disability in Sub-Saharan Africa, but the health economic consequences to victims and health infrastructures serving them remain poorly understood. This information gap is important as it provides an evidence-base guiding national and international health policy decision making on the most cost-effective interventions to better manage snakebite. Here, we assessed hospital-based data to estimate the health economic burden of snakebite in three regions of Burkina Faso (Centre-Ouest, Hauts Bassins and Sud-Ouest).

Methodology

Primary data of snakebite victims admitted to regional and district health facilities (eg, number of admissions, mortality, hospital bed days occupied) was collected in three regions over 17 months in 2013/14. The health burden of snakebite was assessed using Disability-Adjusted Life Years (DALYs) calculations based upon hospitalisation, mortality and disability data from admitted patients amongst other inputs from secondary sources (eg, populations, life-expectancy and age-weighting constants). An activity-based costing approach to determine the direct cost of snake envenoming included unit costs of clinical staff wages, antivenom, supportive care and equipment extracted from context-relevant literature.

Findings

The 10,165 snakebite victims admitted to hospital occupied 28,164 hospital bed days over 17 months. The annual rate of hospitalisation and mortality of admitted snakebite victims was 173 and 1.39/100,000 population, respectively. The estimated annual (i) DALYs lost was 2,153 (0.52/1,000) and (ii) cost to hospitals was USD 506,413 (USD 49/hospitalisation) in these three regions of Burkina Faso. These costs appeared to be influenced by the number of patients receiving antivenom (10.90% in total) in each area (highest in Sud-Ouest) and the type of health facility.

Conclusion

The economic burden of snake envenoming is primarily shouldered by the rural health centres closest to snakebite victims–facilities that are typically least well equipped or resourced to manage this burden. Our study highlights the need for more research in other regions/countries to demonstrate the burden of snakebite and the socioeconomic benefits of its management. This evidence can guide the most cost-effective intervention from government and development partners to meet the snakebite-management needs of rural communities and their health centres.

The World Health Organisation has established a strategy to halve snakebite mortality and morbidity by 2030. Achieving this ambitious target within a decade will require substantial investment from governments of countries most affected by snakebite. The burden of snakebite however, is typically greatest in low-middle income countries with already limited health budgets. Acquiring government support to prioritise snakebite over other prevailing diseases will require evidence of the scale, causes, precise geographies and health economic impacts of snakebite. While the snakebite research community has progressed the delivery of some of these evidence types, it has been weak at providing evidence of the health economic burden of snakebite. Our hospital-based study identifies the health (Disability-Adjusted Life Years) and financial burdens of snakebite to three districts of Burkina Faso. We argue that funding of more health economic research, performed at greater depth and that includes cost-effectiveness of snakebite treatment and other remedial interventions is arguably the most effective tool to advocate for the policy support and investment required of national and international health agencies to deliver WHO’s laudable 2030 target for snakebite.

The application of laboratory-based analytical tools and techniques for the quality assessment and improvement of commercial antivenoms used in the treatment of snakebite envenomation

Snakebite envenomation is a public health problem of high impact, particularly for the developing world. Antivenom, which contains whole or protease-digested immunoglobulin G, purified from the plasma of hyper-immunized animals (mainly horses), is the mainstay for the treatment of snakebite envenomation. The success of antivenom therapy depends upon its ability to abrogate or reduce the local and systemic toxicity of envenomation. In addition, antivenom administration must be safe for the patients. Therefore, antivenom manufacturers must ensure that these products are effective and safe in the treatment of envenomations. Antivenom efficacy and safety are determined by the physicochemical characteristics of formulations, purity of the immunoglobulin fragments and antibodies, presence of protein aggregates, endotoxin burden, preservative load, and batch to batch variation, as well as on the ability to neutralize the most important toxins of the venoms against which the antivenom is designed. In this context, recent studies have shown that laboratory-based simple analytical techniques, for example, size exclusion chromatography, sodium dodecyl sulphate polyacrylamide gel electrophoresis, mass spectrometry, immunological profiling including immuno-turbidimetry and enzyme-linked immunosorbent assays, Western blotting, immune-chromatographic technique coupled to mass spectrometry analysis, reverse-phase high performance liquid chromatography, spectrofluorometric analysis, in vitro neutralization of venom enzymatic activities, and other methodologies, can be applied for the assessment of antivenom quality, safety, stability, and efficacy. This article reviews the usefulness of different analytical techniques for the quality assessment of commercial antivenoms. It is suggested that these tests should be applied for screening the quality of commercial antivenoms before their preclinical and clinical assessment.

Development and characterization of two equine formulations towards SARS-CoV-2 proteins for the potential treatment of COVID-19

In the current global emergency due to SARS-CoV-2 outbreak, passive immunotherapy emerges as a promising treatment for COVID-19. Among animal-derived products, equine formulations are still the cornerstone therapy for treating envenomations due to animal bites and stings. Therefore, drawing upon decades of experience in manufacturing snake antivenom, we developed and preclinically evaluated two anti-SARS-CoV-2 polyclonal equine formulations as potential alternative therapy for COVID-19. We immunized two groups of horses with either S1 (anti-S1) or a mixture of S1, N, and SEM mosaic (anti-Mix) viral recombinant proteins. Horses reached a maximum anti-viral antibody level at 7 weeks following priming, and showed no major adverse acute or chronic clinical alterations. Two whole-IgG formulations were prepared via hyperimmune plasma precipitation with caprylic acid and then formulated for parenteral use. Both preparations had similar physicochemical and microbiological quality and showed ELISA immunoreactivity towards S1 protein and the receptor binding domain (RBD). The anti-Mix formulation also presented immunoreactivity against N protein. Due to high anti-S1 and anti-RBD antibody content, final products exhibited high in vitro neutralizing capacity of SARS-CoV-2 infection, 80 times higher than a pool of human convalescent plasma. Pre-clinical quality profiles were similar among both products, but clinical efficacy and safety must be tested in clinical trials. The technological strategy we describe here can be adapted by other producers, particularly in low- and middle-income countries.

Snakebite Envenoming Diagnosis and Diagnostics

Snakebite envenoming is predominantly an occupational disease of the rural tropics, causing death or permanent disability to hundreds of thousands of victims annually. The diagnosis of snakebite envenoming is commonly based on a combination of patient history and a syndromic approach. However, the availability of auxiliary diagnostic tests at the disposal of the clinicians vary from country to country, and the level of experience within snakebite diagnosis and intervention may be quite different for clinicians from different hospitals. As such, achieving timely diagnosis, and thus treatment, is a challenge faced by treating personnel around the globe. For years, much effort has gone into developing novel diagnostics to support diagnosis of snakebite victims, especially in rural areas of the tropics. Gaining access to affordable and rapid diagnostics could potentially facilitate more favorable patient outcomes due to early and appropriate treatment. This review aims to highlight regional differences in epidemiology and clinical snakebite management on a global scale, including an overview of the past and ongoing research efforts within snakebite diagnostics. Finally, the review is rounded off with a discussion on design considerations and potential benefits of novel snakebite diagnostics.

The development and evaluation of the efficacy of ovine-derived experimental antivenom immunoserum against Macrovipera lebetina obtusa (MLO) venom

Here we describe the processing and development of animal-derived monovalent antibody serum against Macrovipera lebetina obtusa venom by purification and concentration of the immunoglobulins using caprylic acid. We demonstrate that this new viper venom antiserum is pre-clinically effective in neutralizing lethal toxicity and hemorrhagicity of the venom of the Armenian Levantine viper - a significant public health problem in Armenia and a wide region from south-east parts of Europe to south-west Asia. The developed product shows a high capacity to inhibit metalloproteinases and phospholipase activity of venom included in the study in comparison to current specific antivenoms, and following additional experimental approvals, it will be possible to derive the monovalent antivenom satisfying international standards, which will be much cheaper and accessible compared with the current market rivals.

In Vitro Immunological Cross-Reactivity of Thai Polyvalent and Monovalent Antivenoms with Asian Viper Venoms

The intravenous administration of polyclonal antibodies known as antivenom is the only effective treatment for snakebite envenomed victims, but because of inter-specific variation in the toxic components of snake venoms, these therapies have variable efficacies against different snake species and/or different populations of the same species. In this study, we sought to characterize the in vitro venom binding capability and in vitro cross-neutralizing activity of antivenom, specifically the Hemato Polyvalent antivenom (HPAV; The Queen Saovabha Memorial Institute (QSMI) of the Thai Red Cross Society, Thailand) and three monovalent antivenoms (QSMI) specific to Daboia siamensis, Calloselasma rhodostoma, and Trimeresurus albolabris venoms, against a variety of South Asian and Southeast Asian viper venoms (Calloselasma rhodostoma, Daboia russelii, Hypnale hypnale, Trimeresurus albolabris, Trimeresurus purpureomaculatus, Trimeresurus hageni, and Trimeresurus fucatus). Using ELISA and immunoblotting approaches, we find that the majority of protein components in the viper venoms were recognized and bound by the HPAV polyvalent antivenom, while the monospecific antivenom made against T.albolabris extensively recognized toxins present in the venom of related species, T. purpureomaculatus, T. hageni, and T. fucatus. In vitro coagulation assays using bovine plasma revealed similar findings, with HPAV antivenom significantly inhibiting the coagulopathic activities of all tested viper venoms and T. albolabris antivenom inhibiting the venoms from Malaysian arboreal pit vipers. We also show that the monovalent C. rhodostoma antivenom exhibits highly comparable levels of immunological binding and in vitro venom neutralization to venom from both Thailand and Malaysia, despite previous reports of considerable intraspecific venom variation. Our findings suggest that Thai antivenoms from QSMI may by useful therapeutics for managing snake envenomings caused by a number of Southeast Asian viper species and populations for which no specific antivenom currently exists and thus should be explored further to assess their clinical utility in treating snakebite victims.

Bedside Coagulation Tests in Diagnosing Venom-Induced Consumption Coagulopathy in Snakebite

Venom-induced consumption coagulopathy is the most important systemic effect of snake envenoming. Coagulation tests are helpful to accurately and promptly diagnose venom-induced consumption coagulopathy and administer antivenom, which is the only specific treatment available. However, bedside clotting tests play a major role in diagnosing coagulopathy in low-income settings, where the majority of snakebites occur. We conducted a literature search in MEDLINE^® from 1946 to 30 November 2019, looking for research articles describing clinical studies on bedside coagulation tests in snakebite patients. Out of 442 articles identified, 147 articles describing bedside clotting assays were included in the review. Three main bedside clotting tests were identified, namely the Lee–White clotting test, 20-min whole blood clotting time and venous clotting time. Although the original Lee–White clotting test has never been validated for snake envenoming, a recently validated version has been used in some South American countries. The 20-min whole blood clotting time test is the most commonly used test in a wide range of settings and for taxonomically diverse snake species. Venous clotting time is almost exclusively used in Thailand. Many validation studies have methodological limitations, including small sample size, lack of case-authentication, the inclusion of a heterogeneous mix of snakebites and inappropriate uses of gold standard tests. The observation times for bedside clotting tests were arbitrary, without proper scientific justification. Future research needs to focus on improving the existing 20-min whole blood clotting test, and also on looking for alternative bedside coagulation tests which are cheap, reliable and quicker.

New insights into snakebite epidemiology in Costa Rica: A retrospective evaluation of medical records

Continuous monitoring of the snakebite envenoming allows elucidating factors that affect its incidence at spatial and temporal scales, and is a great tool to evaluate the proper management of snakebite in health centers. To determine if there have been changes over time in snakebite epidemiology in Costa Rica, we conducted a retrospective study using medical records from six hospitals for the years 2012-2013. A total of 475 snakebite patients were treated at the selected hospital during this period. Most bites occurred during the rainy season and primarily affected young men, mainly farm workers and schoolchildren. About 55% of bites occur in peri-domiciliary environments, although its prevalence varies geographically. Bothrops asper generates the vast majority of envenoming in the country, which is why the main local symptoms registered are edema, pain, and bleeding disorders. The time elapsed until treatment did not explain the degree of severity at admission. However, complications were observed more frequently in patients who took longer to receive treatment. The primary complications were bacterial infections, whereas kidney failure and compartment syndrome documented at very low frequencies. Only one death was recorded, reflecting the low fatality rate exhibited in the country. Hospital treatment included the rapid administration of antivenom and complementary treatment of antibiotics, analgesics, and antihistamines. The application of the latter as prophylactic does not seem to prevent the appearance of mild early adverse reactions, registered in 22.5% of the cases. Morbidity and mortality rates from snakebite have continued to decrease in the country, as a result of the efforts that Costa Rica has made to improve its public health system. Among those efforts, the creation of primary care centers (EBAIS) has reduced the time to treatment in many regions of the country. The Costa Rican experience of using antivenom in primary health care centers and maintaining good medical records could be considered for application in other countries where snakebite is a major health problem.

An analysis of preclinical efficacy testing of antivenoms for sub-Saharan Africa: Inadequate independent scrutiny and poor-quality reporting are barriers to improving snakebite treatment and management

BACKGROUND

The World Health Organization's strategy to halve snakebite mortality and morbidity by 2030 includes an emphasis on a risk-benefit process assessing the preclinical efficacy of antivenoms manufactured for sub-Saharan Africa. To assist this process, we systematically collected, standardised and analysed all publicly available data on the preclinical efficacy of antivenoms designed for sub-Saharan Africa.

METHODOLOGY/PRINCIPAL FINDINGS

Using a systematic search of publication databases, we focused on publicly available preclinical reports of the efficacy of 16 antivenom products available in sub Saharan Africa. Publications since 1999 reporting the industry standard intravenous pre-incubation method of murine in vivo neutralisation of venom lethality (median effective dose [ED50]) were included. Eighteen publications met the criteria. To permit comparison of the several different reported ED50 values, it was necessary to standardise these to microlitre of antivenom resulting in 50% survival of mice challenged per milligram of venom (μl/mg). We were unable to identify publicly available preclinical data on four antivenoms, whilst data for six polyspecific antivenoms were restricted to a small number of venoms. Only four antivenoms were tested against a wide range of venoms. Examination of these studies for the reporting of key metrics required for interpreting antivenom ED50s were highly variable, as evidenced by eight different units being used for the described ED50 values.

CONCLUSIONS/SIGNIFICANCE

There is a disturbing lack of (i) preclinical efficacy testing of antivenom for sub Saharan Africa, (ii) publicly available reports and (iii) independent scrutiny of this medically important data. Where reports do exist, the methods and metrics used are highly variable. This prevents comprehensive meta-analysis of antivenom preclinical efficacy, and severely reduces the utility of antivenom ED50 results in the decision making of physicians treating patients and of national and international health agencies. Here, we propose the use of a standardised result reporting checklist to resolve this issue. Implementation of these straightforward steps will deliver uniform evaluation of products across laboratories, facilitate meta-analyses, and contribute vital information for designing the clinical trials needed to achieve the WHO target of halving snakebite morbidity and mortality by 2030.

Streamlined downstream process for efficient and sustainable (Fab')2 antivenom preparation

BACKGROUND

Antivenoms are the only validated treatment against snakebite envenoming. Numerous drawbacks pertaining to their availability, safety and efficacy are becoming increasingly evident due to low sustainability of current productions. Technological innovation of procedures generating therapeutics of higher purity and better physicochemical characteristics at acceptable cost is necessary. The objective was to develop at laboratory scale a compact, feasible and economically viable platform for preparation of equine F(ab')2 antivenom against Vipera ammodytes ammodytes venom and to support it with efficiency data, to enable estimation of the process cost-effectiveness.

METHODS

The principle of simultaneous caprylic acid precipitation and pepsin digestion has been implemented into plasma downstream processing. Balance between incomplete IgG breakdown, F(ab')2 over-digestion and loss of the active drug's protective efficacy was achieved by adjusting pepsin to a 1:30 substrate ratio (w/w) and setting pH at 3.2. Precipitation and digestion co-performance required 2 h-long incubation at 21 °C. Final polishing was accomplished by a combination of diafiltration and flow-through chromatography. In vivo neutralization potency of the F(ab')2 product against the venom's lethal toxicity was determined.

RESULTS

Only three consecutive steps, performed under finely tuned conditions, were sufficient for preservation of the highest process recovery with the overall yield of 74%, comparing favorably to others. At the same time, regulatory requirements were met. Final product was aggregate- and pepsin-free. Its composition profile was analyzed by mass spectrometry as a quality control check. Impurities, present in minor traces, were identified mostly as IgG/IgM fragments, contributing to active drug. Specific activity of the F(ab')2 preparation with respect to the plasma was increased 3.9-fold.

CONCLUSION

A highly streamlined mode for production of equine F(ab')2 antivenom was engineered. In addition to preservation of the highest process yield and fulfillment of the regulatory demands, performance simplicity and rapidity in the laboratory setting were demonstrated. Suitability for large-scale manufacturing appears promising.

Animal derived antibodies should be considered alongside convalescent human plasma to deliver treatments for COVID-19

Published data on the first 5,000 coronavirus patients to receive plasma shows promise in the United States. However, delivering convalescent plasma therapies in low- and even middle-income countries is both difficult and costly. Here we discuss the advantages and disadvantages of antisera raised in animals that may allow poorer countries to control the devastating effects of COVID-19.

Antivenom Neutralization of Coagulopathic Snake Venom Toxins Assessed by Bioactivity Profiling Using Nanofractionation Analytics

Venomous snakebite is one of the world's most lethal neglected tropical diseases. Animal-derived antivenoms are the only standardized specific therapies currently available for treating snakebite envenoming, but due to venom variation, often this treatment is not effective in counteracting all clinical symptoms caused by the multitude of injected toxins. In this study, the coagulopathic toxicities of venoms from the medically relevant snake species Bothropsasper, Calloselasmarhodostoma, Deinagkistrodonacutus, Daboiarusselii, Echiscarinatus and Echisocellatus were assessed. The venoms were separated by liquid chromatography (LC) followed by nanofractionation and parallel mass spectrometry (MS). A recently developed high-throughput coagulation assay was employed to assess both the pro- and anticoagulant activity of separated venom toxins. The neutralization capacity of antivenoms on separated venom components was assessed and the coagulopathic venom peptides and enzymes that were either neutralized or remained active in the presence of antivenom were identified by correlating bioassay results with the MS data and with off-line generated proteomics data. The results showed that most snake venoms analyzed contained both procoagulants and anticoagulants. Most anticoagulants were identified as phospholipases A2s (PLA2s) and most procoagulants correlated with snake venom metalloproteinases (SVMPs) and serine proteases (SVSPs). This information can be used to better understand antivenom neutralization and can aid in the development of next-generation antivenom treatments.

Reviewing evidence of the clinical effectiveness of commercially available antivenoms in sub-Saharan Africa identifies the need for a multi-centre, multi-antivenom clinical trial

Background

Snakebite envenoming kills more than more than 20,000 people in Sub-Saharan Africa every year. Poorly regulated markets have been inundated with low-price, low-quality antivenoms. This review aimed to systematically collect and analyse the clinical data on all antivenom products now available in markets of sub-Saharan Africa.

Methodology/Principal findings

Our market analysis identified 12 polyspecific and 4 monospecific antivenom products in African markets. Our search strategy was first based on a systematic search of publication databases, followed by manual searches and discussions with experts. All types of data, including programmatic data, were eligible. All types of publications were eligible, including grey literature. Cohorts of less than 10 patients were excluded. 26 publications met the inclusion criteria. Many publications had to be excluded because clinical outcomes were not clearly linked to a specific product. Our narrative summaries present product-specific clinical data in terms of safety and effectiveness against the different species and envenoming syndromes. Three products (EchiTabPlus, EchiTabG, SAIMR-Echis-monovalent) were found to have been tested in robust clinical studies and found effective against envenoming caused by the West African carpet viper (Echis ocellatus). Four products (Inoserp-Panafricain, Fav-Afrique, SAIMR-Polyvalent, Antivipmyn-Africa) were found to have been evaluated only in observational single-arm studies, with varying results. For nine other products, there are either no data in the public domain, or only negative data suggesting a lack of effectiveness.

Conclusions/Significance

Clinical data vary among the different antivenom products currently in African markets. Some products are available commercially although they have been found to lack effectiveness. The World Health Organization should strengthen its capacity to assess antivenom products, support antivenom manufacturers, and assist African countries and international aid organizations in selecting appropriate quality antivenoms.

Snakebite envenomation represents one of the most neglected tropical medical conditions worldwide. Despite high levels of morbidity and mortality associated with snakebite, its neglected nature has compromised the availability and evaluation of antivenom treatment. This review was initiated by Médecins Sans Frontières’ / Doctors Without Borders (MSF) Access Campaign, as the existing antivenom access crisis in sub-Saharan Africa was deepening. This study sought to review the clinical data pertaining to each antivenom product currently available for use in sub-Saharan Africa. 16 different antivenoms were identified. A total of 26 studies met the inclusion criteria. Given the heterogeneity of study methodology and quality, data for individual antivenoms are presented in the form of a narrative analysis. Only two studies reported clinical data collected from randomized controlled trials. Consistent monitoring of the side effects of antivenom treatment was lacking. The absence of good quality data for the majority of antivenoms in sub-Saharan Africa is a major concern. Further robust data collection is required, while urgent investments are needed at the global level to ensure a sustained production of safe and effective antivenom treatment, and its affordable access across sub-Saharan Africa.

Refinement strategy for antivenom preparation of high yield and quality

Antivenoms from hyperimmune animal plasma are the only specific pharmaceuticals against snakebites. The improvement of downstream processing strategies is of great interest, not only in terms of purity profile, but also from yield-to-cost perspective and rational use of plasma of animal origin. We report on development of an efficient refinement strategy for F(ab')2-based antivenom preparation. Process design was driven by the imperative to keep the active principle constantly in solution as a precautionary measure to preserve stability of its conformation (precipitation of active principle or its adsorption to chromatographic stationary phase has been completely avoided). IgG was extracted from hyperimmune horse plasma by 2% (V/V) caprylic acid, depleted from traces of precipitating agent and digested by pepsin. Balance between incomplete IgG fraction breakdown, F(ab')2 over-digestion and loss of the active principle's protective efficacy was achieved by adjusting pepsin to substrate ratio at the value of 4:300 (w/w), setting pH to 3.2 and incubation period to 1.5 h. Final polishing was accomplished by a combination of diafiltration and flow-through chromatography. Developed manufacturing strategy gave 100% pure and aggregate-free F(ab')2 preparation, as shown by size-exclusion HPLC and confirmed by MS/MS. The overall yield of 75% or higher compares favorably to others so far reported. This optimised procedure looks also promising for large-scale production of therapeutic antivenoms, since high yield of the active drug and fulfillment of the regulatory demand considering purity was achieved. The recovery of the active substance was precisely determined in each purification step enabling accurate estimation of the process cost-effectiveness.

The validity, reliability and minimal clinically important difference of the patient specific functional scale in snake envenomation

Objective

Valid, reliable, and clinically relevant outcome measures are necessary in clinical studies of snake envenomation. The aim of this study was to evaluate the psychometric (validity and reliability) and clinimetric (minimal clinically important difference [MCID]) properties of the Patient-Specific Functional Scale (PSFS) in snakebite envenomation.

Methods

We performed a secondary analysis of two existing snakebite trials that measured clinical outcomes using the PSFS as well as other quality of life and functional assessments. Data were collected at 3, 7, 10, and 17 days. Reliability was determined using Cronbach’s alpha for internal consistency and the intraclass correlation coefficient (ICC) for temporal stability at 10 and 17 days. Validity was assessed using concurrent validity correlating with the other assessments. The MCID was evaluated using the following criteria: (1) the distribution of stable patients according to both standard error of measurement (SEM) and responsiveness techniques, and (2) anchor-based methods to compare between individuals and to detect discriminant ability of a positive change with a receiver operator characteristic (ROC) curve and optimal cutoff point.

Results

A total of 86 patients were evaluated in this study. The average PSFS scores were 5.37 (SD 3.23), 7.95 (SD 2.22), and 9.12 (SD 1.37) at 3, 7, and 10 days, respectively. Negligible floor effect was observed (maximum of 8% at 3 days); however, a ceiling effect was observed at 17 days (25%). The PSFS showed good reliability with an internal consistency of 0.91 (Cronbach’s alpha) (95% CI 0.88, 0.95) and a temporal stability of 0.83 (ICC) (95% CI 0.72, 0.89). The PSFS showed a strong positive correlation with quality of life and functional assessments. The MCID was approximately 1.0 for all methods.

Conclusions

With an MCID of approximately 1 point, the PSFS is a valid and reliable tool to assess quality of life and functionality in patients with snake envenomation.

The snakebite problem and antivenom crisis from a health-economic perspective

The scourge of snakebite has been well documented but largely ignored by the global health community for several decades, especially the role that economics has played in causing and exacerbating this crisis. Every year millions of people in low and middle-income countries face death, disability and disadvantage from snakebite envenoming (SBE) without access to appropriate treatment. Health-economic factors pervade every aspect of this neglected problem. A multitude of financial and commercial factors helped to cause, and now perpetuate, shortages of high quality, affordable and region-appropriate antivenom in areas where they are most needed. Alongside the death, physical disability and psychological anguish from SBE is a debilitating financial toll, which includes both direct costs of treatment and indirect costs from lost income. SBE is a problem that disproportionately affects poor, rural and agrarian communities, with most victims being young and industrious subsistence workers. The burden of envenoming is often felt by families and communities that can least afford it, and negatively impacts local and national productivity. The lack of long-term investment in health systems to properly manage SBE has led to insufficient funding for antivenom development, procurement, quality control and distribution, despite highly favourable cost effectiveness of some antivenoms. This has contributed to market failures that have seen antivenom output fall and become inaccessible to most victims. Solutions to these problems exist and are achievable, however the challenge for advocates is to appreciate the importance of health-economics and ensure that strategies to redress the economic causes and consequences of SBE are themselves cost-effective and financially sustainable.

Delayed double reading of whole blood clotting test (WBCT) results at 20 and 30 minutes enhances diagnosis and treatment of viper envenomation

Background

The whole blood clotting test (WBCT) is a simple test of coagulation that is often used in the assessment, diagnosis, and therapeutic monitoring of snakebite patients in sub-Saharan Africa. WBCT requires only a clean glass tube and several milliliters of venous blood and is ideal for use in poorly equipped health centers throughout the rural areas where 95% of snakebites occur. However, questions surrounding the accuracy and reliability of the test remain unanswered due to variations in testing conditions and a lack of comparative research with which to validate them. This is the first study to evaluate WBCT results at both 20-min (WBCT20) and 30-min (WBCT30) reading times in the same group of snakebite patients.

Methods

In order to define the best reading time, the authors compared the results of serial WBCT evaluation at both 20 and 30 min after collection in 23 patients treated for snake envenomation in Bembèrèkè, northern Benin.

Results

WBCT results were identical at both reading times in patients without coagulopathy or when coagulation was restored permanently following a single dose of antivenom. Out of 17 patients with coagulopathy, 14 showed discrepancies between WBCT20 and WBCT30 results in at least one pair of serial evaluations. These could be completely contradictory results (e.g. normal clot at WBCT20 and no clot at WBCT30) or a marked difference in the quality of the clot (e.g. no clotting activity at WBCT20 and an unstable partial clot at WBCT30). WBCT discrepancies were encountered most frequently in three situations: initial normalization of hemostasis following antivenom therapy, detection of a secondary resumption of coagulopathy, or final restoration of hemostasis after a secondary resumption had occurred.

Conclusions

This study suggests that the WBCT is robust and that a sequential reading should improve the diagnosis and monitoring of venom-induced coagulopathies. It also indicates the possibility of discrepancies in the sensitivity of WBCT20 and WBCT30 for detecting the resolution or reoccurrence of coagulopathy and identifies how these findings, if confirmed, may be used to increase the efficacy and efficiency of antivenom treatment in the field.

Clinical studies of the effectiveness and safety of antivenoms

In the 1890s, hyperimmune sera proved effective in animals against challenge by the snake venom against which they had been raised. They were first used, apparently successfully, in a human patient in about 1895. Since then, antivenoms have become accepted as the only reliable specific treatment for snake-bite envenoming. Despite decades of accumulated clinical experience and a number of published randomized comparative and observational studies, the clinical effectiveness and safety of some antivenoms remain open to question, due to a lack of robust randomized controlled trial data. Antivenoms in some poorly regulated markets may have high rates of potentially fatal adverse effects and their use must be balanced by demonstrable effectiveness. Even those manufactured to strict regulatory requirements may pose a rare risk of severe adverse reactions. Most antivenoms currently marketed around the world were registered without first being studied clinically. There is increasing pressure to subject antivenoms, even those that are long-established, to the same protocols of rigorous pre-clinical and clinical assessment that are standard regulatory requirements for other drugs. Conventional clinical testing progresses through Phases I, II, III to IV. Most authorities consider antivenoms too dangerous to be used in Phase I studies in healthy volunteers. An alternative method for preliminary estimation of safety, dose-finding and effectiveness, is proposed - the "3 + 3" dose escalation or de-escalation design, in volunteer patients, as used in oncology to test cytotoxic drugs. Antivenoms are so widely used and well trusted, that there are few ethical justifications for placebo controls. However, placebo might be ethically justified if there were no proven effective treatment and or if withholding or delaying treatment posed acceptably negligible risks to the participants. Antivenom trials are most urgently needed in low-to middle-income countries where there are many practical, logistical and funding challenges. Basic requirements for clinical trials include identification of the biting species of snake in every case; the use of objective, clinically-relevant endpoints, such as restoration of blood coagulability; definition of inclusion, exclusion and withdrawal criteria; assurance of antivenom safety; ethical considerations; inclusion of one or more control (comparator) groups; and analysis based on intention to treat. The highest quality evidence comes from Phase II and larger Phase III studies that have been designed as statistically powerful, randomized, controlled trials (RCTs), ideally with blinding of patients and investigators to avoid bias. Because of the challenges to carrying out clinical trials of antivenoms, Phase IV trials (post-marketing surveillance) are potentially more important and useful than for most other drugs.

Snakebite: When the Human Touch Becomes a Bad Touch

Many issues and complications in treating snakebite are a result of poor human social, economic and clinical intervention and management. As such, there is scope for significant improvements for reducing incidence and increasing patient outcomes. Snakes do not target humans as prey, but as our dwellings and farms expand ever farther and climate change increases snake activity periods, accidental encounters with snakes seeking water and prey increase drastically. Despite its long history, the snakebite crisis is neglected, ignored, underestimated and fundamentally misunderstood. Tens of thousands of lives are lost to snakebites each year and hundreds of thousands of people will survive with some form of permanent damage and reduced work capacity. These numbers are well recognized as being gross underestimations due to poor to non-existent record keeping in some of the most affected areas. These underestimations complicate achieving the proper recognition of snakebite’s socioeconomic impact and thus securing foreign aid to help alleviate this global crisis. Antivenoms are expensive and hospitals are few and far between, leaving people to seek help from traditional healers or use other forms of ineffective treatment. In some cases, cheaper, inappropriately manufactured antivenom from other regions is used despite no evidence for their efficacy, with often robust data demonstrating they are woefully ineffective in neutralizing many venoms for which they are marketed for. Inappropriate first-aid and treatments include cutting the wound, tourniquets, electrical shock, immersion in ice water, and use of ineffective herbal remedies by traditional healers. Even in the developed world, there are fundamental controversies including fasciotomy, pressure bandages, antivenom dosage, premedication such as adrenalin, and lack of antivenom for exotic snakebites in the pet trade. This review explores the myriad of human-origin factors that influence the trajectory of global snakebite causes and treatment failures and illustrate that snakebite is as much a sociological and economic problem as it is a medical one. Reducing the incidence and frequency of such controllable factors are therefore realistic targets to help alleviate the global snakebite burden as incremental improvements across several areas will have a strong cumulative effect.

Preclinical antivenom-efficacy testing reveals potentially disturbing deficiencies of snakebite treatment capability in East Africa

BACKGROUND

Antivenom is the treatment of choice for snakebite, which annually kills an estimated 32,000 people in sub-Saharan Africa and leaves approximately 100,000 survivors with permanent physical disabilities that exert a considerable socioeconomic burden. Over the past two decades, the high costs of the most polyspecifically-effective antivenoms have sequentially reduced demand, commercial manufacturing incentives and production volumes that have combined to create a continent-wide vacuum of effective snakebite therapy. This was quickly filled with new, less expensive antivenoms, many of which are of untested efficacy. Some of these successfully marketed antivenoms for Africa are inappropriately manufactured with venoms from non-African snakes and are dangerously ineffective. The uncertain efficacy of available antivenoms exacerbates the complexity of designing intervention measures to reduce the burden of snakebite in sub-Saharan Africa. The objective of this study was to preclinically determine the ability of antivenoms available in Kenya to neutralise the lethal effects of venoms from the most medically important snakes in East Africa.

METHODS

We collected venom samples from the most medically important snakes in East Africa and determined their toxicity in a mouse model. Using a 'gold standard' comparison protocol, we preclinically tested the comparative venom-neutralising efficacy of four antivenoms available in Kenya with two antivenoms of clinically-proven efficacy. To explain the variant efficacies of these antivenoms we tested the IgG-venom binding characteristics of each antivenom using in vitro IgG titre, avidity and venom-protein specificity assays. We also measured the IgG concentration of each antivenom.

FINDINGS

None of the six antivenoms are preclinically effective, at the doses tested, against all of the most medically important snakes of the region. The very limited snake polyspecific efficacy of two locally available antivenoms is of concern. In vitro assays of the abilities of 'test' antivenom IgGs to bind venom proteins were not substantially different from that of the 'gold standard' antivenoms. The least effective antivenoms had the lowest IgG content/vial.

CONCLUSIONS

Manufacture-stated preclinical efficacy statements guide decision making by physicians and antivenom purchasers in sub-Saharan Africa. This is because of the lack of both clinical data on the efficacy of most of the many antivenoms used to treat patients and independent preclinical assessment. Our preclinical efficacy assessment of antivenoms available in Kenya identifies important limitations for two of the most commonly-used antivenoms, and that no antivenom is preclinically effective against all the regionally important snakes. The potential implication to snakebite treatment is of serious concern in Kenya and elsewhere in sub-Saharan Africa, and underscores the dilemma physicians face, the need for clinical data on antivenom efficacy and the medical and societal value of establishing independent preclinical antivenom-efficacy testing facilities throughout the continent.

Snakebite envenoming

Snakebite envenoming is a neglected tropical disease that kills >100,000 people and maims >400,000 people every year. Impoverished populations living in the rural tropics are particularly vulnerable; snakebite envenoming perpetuates the cycle of poverty. Snake venoms are complex mixtures of proteins that exert a wide range of toxic actions. The high variability in snake venom composition is responsible for the various clinical manifestations in envenomings, ranging from local tissue damage to potentially life-threatening systemic effects. Intravenous administration of antivenom is the only specific treatment to counteract envenoming. Analgesics, ventilator support, fluid therapy, haemodialysis and antibiotic therapy are also used. Novel therapeutic alternatives based on recombinant antibody technologies and new toxin inhibitors are being explored. Confronting snakebite envenoming at a global level demands the implementation of an integrated intervention strategy involving the WHO, the research community, antivenom manufacturers, regulatory agencies, national and regional health authorities, professional health organizations, international funding agencies, advocacy groups and civil society institutions.

Differential procoagulant effects of saw-scaled viper (Serpentes: Viperidae: Echis) snake venoms on human plasma and the narrow taxonomic ranges of antivenom efficacies

Saw-scaled vipers (genus Echis) are one of the leading causes of snakebite morbidity and mortality in parts of Sub-Saharan Africa, the Middle East, and vast regions of Asia, constituting a public health burden exceeding that of almost any other snake genus globally. Venom-induced consumption coagulopathy, owing to the action of potent procoagulant toxins, is one of the most relevant clinical manifestations of envenomings by Echis spp. Clinical experience and prior studies examining a limited range of venoms and restricted antivenoms have demonstrated for some antivenoms an extreme lack of antivenom cross-reactivity between different species of this genus, sometimes resulting in catastrophic treatment failure. This study undertook the most comprehensive testing of Echis venom effects upon the coagulation of human plasma, and also the broadest examination of antivenom potency and cross-reactivity, to-date. 10 Echis species/populations and four antivenoms (two African, two Asian) were studied. The results indicate that the venoms are, in general, potently procoagulant but that the relative dependence on calcium or phospholipid cofactors is highly variable. Additionally, three out of the four antivenoms tested demonstrated only a very narrow taxonomic range of effectiveness in preventing coagulopathy, with only the SAIMR antivenom displaying significant levels of cross-reactivity. These results were in conflict with previous studies using prolonged preincubation of antivenom with venom to suggest effective cross-reactivity levels for the ICP Echi-Tab antivenom. These findings both inform upon potential clinical effects of envenomation in humans and highlight the extreme limitations of available treatment. It is hoped that this will spur efforts into the development of antivenoms with more comprehensive coverage for bites not only from wild snakes but also from specimens widely kept in zoological collections.