An open, randomized comparative trial of two antivenoms for the treatment of envenoming by Sri Lankan Russell's viper (Daboia russelii russelii)

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.

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.

Assessment of quality and pre-clinical efficacy of a newly developed polyvalent antivenom against the medically important snakes of Sri Lanka

Snake envenomation is a severe problem in Sri Lanka (SL) and Indian polyvalent antivenom (PAV) is mostly used for treating snakebite albeit due to geographical variation in venom composition, Indian PAV shows poor efficacy in neutralizing the lethality and toxicity of venom from the same species of snakes in SL. Therefore, the quality and in vivo venom neutralization potency of a country-specific PAV produced against the venom of the five most medically important snakes of SL (Daboia russelii, Echis carinatus, Hypnale hypnale, Naja naja, Bungarus caeruleus) was assessed. LC-MS/MS analysis of two batches of PAV showed the presence of 88.7-97.2% IgG and traces of other plasma proteins. The tested PAVs contained minor amounts of undigested IgG and F(ab')2 aggregates, showed complement activation, were devoid of IgE, endotoxin, and content of preservative was below the threshold level. Immunological cross-reactivity and in vitro neutralization of enzymatic activities, pharmacological properties demonstrated superior efficacy of SL PAV compared to Indian PAV against SL snake venoms. The in vivo neutralization study showed that the tested PAVs are potent to neutralize the lethality and venom-induced toxicity of SL snake venoms. Therefore, our study suggests that introduction of SL-specific PAV will improve snakebite management in SL.

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.

Comparison of rotational thromboelastometry parameters with 20-minute whole blood clotting test as a predictor of envenoming in Russell's viper bite patients

BACKGROUND

Coagulopathy is an important and common systemic clinical syndrome caused by snake envenoming. The major clinical effect of Russell's viper (RV) envenoming is haematotoxicity. The 20-min whole blood clotting test (WBCT20) is the standard test for identification of envenoming in resource-limited settings. However, its reliability as a diagnostic test has been questioned. Rotational thromboelastometry (ROTEM) assays different phases of clot formation from initiation to fibrinolysis. Our objective was to compare parameters of ROTEM with WBCT20 and the international normalized ratio (INR) as predictors of envenoming in RV bite patients.

METHODS

Fifty-three patents with RV bite presenting to Anuradhapura Hospital, Sri Lanka were recruited. Epidemiological and clinical data were obtained. Venous blood samples were collected at admission for ROTEM, INR and WBCT20.

RESULTS

A total of 46 of 53 patients with RV bites received antivenom serum (AVS); 74% had a non-clottable WBCT20. All 46 had at least one abnormal ROTEM parameter and 93% had a prolonged EXTEM clotting time (EXTEM-CT). The sensitivity of a prolonged INR was only 55%.

CONCLUSIONS

EXTEM-CT is a better predictor of envenoming and the need for AVS than WBCT20 in RV bites (p=0.02). It provides a numerical value that can be used post-AVS to objectively assess the response and decide on further treatment.

Determinants of snakebite mortality in Asia: A systematic review

PURPOSE

This systemic review summarizes the evidence exploring the determinants of mortality due to snakebite envenomation in Asia.

MATERIALS AND METHODS

The database PubMed, Web of Science and Science Direct were searched to identify the relevant literatures concerning mortality due to snakebites mortality in Asia. All the articles chosen were critically appraised for its quality using a mixed-method assessment tool by two independent reviewers with discrepancies sorted by a third person.

RESULTS

A total of 7 studies were included in the final analysis which was 3 cross-sectional studies, 2 case reports, 1 observation prospective study and 1 randomized control trial study. Two studies were conducted in India and two studies in Sri Lanka while one study was conducted in Taiwan, Vietnam and Nepal respectively. The cases of snakebite victims were retrieved from the year of 1987 until 2017. In total, there were 762 cases of snakebite victims recorded, with 61 of those victims succumbed to death. From the final total of 7 studies, 4 of the studies showed snakebites mortality were related to delayed treatment access and 3 studies due to suboptimal care.

CONCLUSION

Mortality and morbidity can be reduced if there is a quick access for victims to emergency medical care, rapid transfer time to hospital and receiving immediate optimal medical treatment from trained medical staff once in the hospital or dispensary.

Risk factors associated with snake antivenom reaction and the role of skin test

Antivenom reactions are a common complication of snake antivenom. This study aimed to identify predicators of antivenom reaction and the involvement of antivenom skin test in antivenom reaction development. This retrospective cohort study was conducted in six medical institutions in Taiwan. Data were extracted from the Chang Gung Research Database (CGRD) from January 2006 to December 2016. The association between antivenom reaction and patient demographics, type and dose of antivenom, and skin test results was analyzed. The study enrolled 799 patients, including 219 who developed antivenom reactions. Compared to patients receiving both freeze-dried hemorrhagic (FH) and freeze-dried neurotoxic (FN) antivenom, those administered a single type had a lower antivenom reaction risk (adjusted odds ratios [aORs]: 0.5 and 0.4, 95% confidence interval [CI]: 0.35-0.74 and 0.24-0.69, FH and FN respectively). Patients administered a higher antivenom dose (≥ 5 vials) had higher antivenom reaction risk (aOR: 1.8, 95% CI: 1.23-2.76). A positive skin test result was also associated with antivenom reaction (aOR: 16.7, 95% CI: 5.42-51.22). The skin test showed high specificity (98.5%, 95% CI: 97.49%-99.83%) but low sensitivity (17.5%, 95% CI: 10.74%-24.18%). The antivenom skin test should be abolished because of the extremely low sensitivity and possible misinterpretation of results because of the limitation of this examination.

Comparación de la eficacia, la seguridad y la farmacocinética de los antivenenos antiofídicos: revisión de literatura

En Colombia se presentan anualmente alrededor de 5000 casos de mordedura de serpiente y su tratamiento se basa en la neutralización con inmunoglobulinas completas purificadas, sin embargo, globalmente se utilizan antivenenos faboterápicos. Objetivo: Dar a conocer diferencias entre las generaciones de antivenenos, la importancia del veneno en la producción de anticuerpos, comparar aspectos farmacocinéticos y los efectos adversos en pacientes. Materiales Métodos: Se realizó una búsqueda de literatura en bases de datos utilizando combinaciones de los descriptores y términos Mesh, en inglés y español. Se cotejaron parámetros farmacocinéticos en estudios preclínicos y los efectos adversos en estudios clínicos. Resultados: Se encontraron diferencias debidas al tamaño de la fracción de la inmunoglobulina que la compone, así entre más pequeña es ésta, se observa mayor distribución a los tejidos y una vida media más corta, comparada con las moléculas más pesadas. Se encontraron estudios con disminución de efectos adversos con antivenenos faboterápicos 

Clinico-epidemiology and management of Russell's viper (Daboia russelii) envenoming in dogs in Sri Lanka

INTRODUCTION

Russell's viper envenoming in dogs is a significant problem in Sri Lanka. The current study focused on investigating clinical profile, laboratory findings of three selected tests and to develop a treatment strategy with Indian polyvalent Anti-Venom Serum (AVS). It was also intended to report adverse effects and complications caused by both Russell's viper venom (RVV) and AVS in Russell's Viper (RV) envenomed dogs.

OBJECTIVE

To evaluate and report the clinical manifestations, to find out the minimum effective vials of AVS and to record AVS induced adverse reactions of RV envenoming in dogs.

MATERIALS AND METHODS

A prospective study was conducted on Russell's viper bitten dogs (n = 65) admitted to the Veterinary Teaching Hospital (VTH) in Sri Lanka. Indian polyvalent AVS was used to treat all the envenomed dogs. The number of vials of AVS that was administered to a patient was decided upon by a second degree polynomial model with a number of vials of AVS in the X axis verses Prothrombine Time (PT), Activated Partial Thromboplastine Time (aPTT) and Clotting Time (CT) in the Y axis respectively.

RESULTS

Varying degrees of pain were exhibited by all the victim dogs. Mild swelling and necrosis at the site of bite was seen in 54% (n = 35) and 37% (n = 24) of dogs respectively. Prolonged values of, PT, aPTT and CT were seen from all the RV envenomed dogs. The mean leukocyte count in these dogs was 39.79 × 103/μL (normal range; 4-20 × 103/μL) (IQR:29.05 × 103/μL-45.92 × 103/μL). Statistical analysis showed that the initial vials of 7 AVS would be the minimum required vials. Therefore, a range of 6-15 AVS vials in total were administered to these dogs and in 7.6% (n = 5) of dogs, the results of PT, aPTT and CT became normal with 6 AVS vials at 32-97 minutes. Acute Renal Failure (ARF) was detected from 29% (n = 19) of dogs as a complication.

CONCLUSIONS

Systemic clinical signs of haemorrhagic lesions, cardio respiratory toxicities were common in Russell's viper envenomed dogs. Initially 6 vials of AVS must be administered. AVS induced reactions were reported commonly. Russell's viper envenoming was found to be lethal in dogs.

Biosynthetic Oligoclonal Antivenom (BOA) for Snakebite and Next-Generation Treatments for Snakebite Victims

Snakebite envenoming is a neglected tropical disease that each year claims the lives of 80,000–140,000 victims worldwide. The only effective treatment against envenoming involves intravenous administration of antivenoms that comprise antibodies that have been isolated from the plasma of immunized animals, typically horses. The drawbacks of such conventional horse-derived antivenoms include their propensity for causing allergenic adverse reactions due to their heterologous and foreign nature, an inability to effectively neutralize toxins in distal tissue, a low content of toxin-neutralizing antibodies, and a complex manufacturing process that is dependent on husbandry and procurement of snake venoms. In recent years, an opportunity to develop a fundamentally novel type of antivenom has presented itself. By using modern antibody discovery strategies, such as phage display selection, and repurposing small molecule enzyme inhibitors, next-generation antivenoms that obviate the drawbacks of existing plasma-derived antivenoms could be developed. This article describes the conceptualization of a novel therapeutic development strategy for biosynthetic oligoclonal antivenom (BOA) for snakebites based on recombinantly expressed oligoclonal mixtures of human monoclonal antibodies, possibly combined with repurposed small molecule enzyme inhibitors.

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.

Recent Advances in Next Generation Snakebite Antivenoms

With the inclusion of snakebite envenoming on the World Health Organization’s list of Neglected Tropical Diseases, an incentive has been established to promote research and development effort in novel snakebite antivenom therapies. Various technological approaches are being pursued by different research groups, including the use of small molecule inhibitors against enzymatic toxins as well as peptide- and oligonucleotide-based aptamers and antibody-based biotherapeutics against both enzymatic and non-enzymatic toxins. In this article, the most recent advances in these fields are presented, and the advantages, disadvantages, and feasibility of using different toxin-neutralizing molecules are reviewed. Particular focus within small molecules is directed towards the inhibitors varespladib, batimastat, and marimastat, while in the field of antibody-based therapies, novel recombinant polyclonal plantivenom technology is discussed.

A prospective cohort study of the effectiveness of the primary hospital management of all snakebites in Kurunegala district of Sri Lanka

INTRODUCTION

Sri Lanka records substantial numbers of snakebite annually. Primary rural hospitals are important contributors to health care. Health care planning requires a more detailed understanding of snakebite within this part of the health system. This study reports the management and epidemiology of all hospitalised snakebite in the Kurunegala district in Sri Lanka.

METHODOLOGY

The district has 44 peripheral/primary hospitals and a tertiary care hospital-Teaching Hospital, Kurunegala (THK). This prospective study was conducted over one year. All hospitals received copies of the current national guidelines on snakebite management. Clinical and demographic details of all snakebite admissions to primary hospitals were recorded by field researchers and validated by comparing with scanned copies of the medical record. Management including hospital transfers was independently assessed against the national guidelines recommendation. Population rates were calculated and compared with estimates derived from recent community based surveys.

RESULTS

There were 2186 admissions of snakebites and no deaths in primary hospitals. An additional 401 patients from the district were admitted directly to the teaching hospital, 2 deaths were recorded in this group. The population incidence of hospitalized snakebite was 158/100,000 which was significantly lower than community survey estimates of 499/100,000. However there was no significant difference between the incidence of envenomation of 126/100,000 in hospitalised patients and 184/100,000 in the community survey. The utilisation of antivenom was appropriate and consistent with guidelines. Seventy patients received antivenom. Anaphylactic reactions to antivenom occurred in 22 patients, treatment reactions was considered to be outside the guidelines in 5 patients. Transfers from the primary hospital occurred in 399(18%) patients but the majority (341) did not meet the guideline criteria. A snake was identified in 978 cases; venomous snakebites included 823 hump-nosed viper (Hypnalespp), 61 Russell's viper, 14 cobra, 13 common krait, 03 saw scaled viper.

CONCLUSIONS

Primary hospitals received a significant number of snakebites that would be missed in surveys conducted in tertiary hospitals. Adherence to guidelines was good for the use of antivenom but not for hospital transfer or treatment of anaphylaxis. The large difference in snakebite incidence between community and hospital studies could possibly be due to non-envenomed patients not presenting. As the majority of snakebite management occurs in primary hospitals education and clinical support should be focused on that part of the health system.

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.

Characterization of Daboia russelii and Naja naja venom neutralizing ability of an undocumented indigenous medication in Sri Lanka

Background

Indigenous medicinal practice in Sri Lanka talks about powerful compounds extracted from native plants for treating venomous snake bites which are hardly documented in literature but are used by the indigenous doctors for thousand years.

Objective

We screened the neutralizing ability of a herbal preparation practiced in indigenous medicine of Sri Lanka, consisting of Sansevieria cylindrica, Jatropha podagrica and Citrus aurantiifolia, for its ability to neutralize venom toxins of Naja naja (Common Cobra) and Daboia russelii (Russell's viper).

Materials and methods

The venom toxicity was evaluated using a 5-day old chicken embryo model observing the pathophysiology and the mortality for six hours, in the presence or absence of the herbal preparation. The known toxin families to exist in snake venom, such as Phospholipase A₂, Snake venom Metalloprotease, were evaluated to understand the mechanism of venom neutralizing ability of the herbal preparation.

Results

The LD₅₀ of D. russelii venom, as measured using the 5-day old chicken embryo model, was 4.8 ± 0.865 ug (R² = 84.8%, P = 0.079). The pre-incubation of venom with the herbal preparation increased the LD₅₀ of D. russelii venom to 17.64 ± 1.35 μg (R² = 81.0%, P = 0.100), showing a clear neutralizing action of D. russelii venom toxicity by the herbal medicine. Whereas the pre-incubation of venom with the 1× venom neutralizing dose of commercially available polyvalent anti-venom serum shifted the LD₅₀ venom only up to 5.5 ± 1.35 μg (R² = 98.8%, P = 0.069). In the presence of the herbal preparation, Phospholipase A₂ activity of D. russelii venom was significantly reduced from 9.2 × 10⁻³ mM min⁻¹ to 8.0 × 10⁻³ mM min⁻¹ and that of N. naja from 2.92 × 10⁻² mM min⁻¹ to 0.188 × 10⁻² mM min⁻¹. Further, the pre-incubation of N. naja venom with the herbal preparation significantly reduced its Metalloprotease activity from 0.069 units min⁻¹ to 0.019 units min⁻¹.

Conclusion

The herbal preparation shows a clear neutralizing action against the toxicities of D. russelii and N. naja venoms demonstrating the potential to be used as a plant based antidote for snake envenomation.

Development of a new polyspecific antivenom for snakebite envenoming in Sri Lanka: Analysis of its preclinical efficacy as compared to a currently available antivenom

A new whole IgG, freeze-dried, polyspecific antivenom was prepared from the plasma of horses immunized with the venoms of the snakes Daboia russelii, Echis carinatus, Hypnale hypnale, and Naja naja from Sri Lanka. The preclinical neutralizing ability of this antivenom against several toxic and enzymatic activities of these four venoms was analyzed, and compared with that of a batch of VINS antivenom (India) being currently used in Sri Lanka. The activities tested were: lethality, hemorrhagic, in vitro coagulant, proteinase and phospholipase A₂. Both antivenoms neutralized, to a different extent, these activities of the venom of D. russelii, E. carinatus, and N. naja. In general, the polyspecific Sri Lankan antivenom was more effective than the Indian antivenom in the neutralization of the venoms of D. russelii and E. carinatus, whereas the Indian antivenom showed a higher efficacy against the venom of N. naja. Regarding H. hypnale, the new Sri Lankan antivenom was effective in the neutralization of all activities tested, whereas the Indian antivenom neutralized lethality but not hemorrhagic, coagulant, proteinase and PLA₂ activities, in agreement with the fact that this venom is not included in the immunization mixture for this antivenom. Results suggest that the new polyspecific Sri Lankan antivenom has a satisfactory preclinical neutralizing profile and compares favorably with the Indian antivenom. This is ready to be tested in a clinical trial to evaluate its efficacy and safety in human victims of snakebite envenomings by D. russelii, E. carinatus and H. hypnale in Sri Lanka.

Neurotoxicity in Russell's viper (Daboia russelii) envenoming in Sri Lanka: a clinical and neurophysiological study

CONTEXT

Russell's viper is more medically important than any other Asian snake, due to number of envenoming's and fatalities. Russell's viper populations in South India and Sri Lanka (Daboia russelii) cause unique neuromuscular paralysis not seen in other Russell's vipers.

OBJECTIVE

To investigate the time course and severity of neuromuscular dysfunction in definite Russell's viper bites, including antivenom response.

METHODOLOGY

We prospectively enrolled all patients (>16 years) presenting with Russell's viper bites over 14 months. Cases were confirmed by snake identification and/or enzyme immunoassay. All patients had serial neurological examinations and in some, single fibre electromyography (sfEMG) of the orbicularis oculi was performed.

RESULTS

245 definite Russell's viper bite patients (median age: 41 years; 171 males) presented a median 2.5 h (interquartile range: 1.75-4.0 h) post-bite. All but one had local envenoming and 199 (78%) had systemic envenoming: coagulopathy in 166 (68%), neurotoxicity in 130 (53%), and oliguria in 19 (8%). Neurotoxicity was characterised by ptosis (100%), blurred vision (93%), and ophthalmoplegia (90%) with weak extraocular movements, strabismus, and diplopia. Neurotoxicity developed within 8 h post-bite in all patients. No bulbar, respiratory or limb muscle weakness occurred. Neurotoxicity was associated with bites by larger snakes (p < 0.0001) and higher peak serum venom concentrations (p = 0.0025). Antivenom immediately decreased unbound venom in blood. Of 52 patients without neurotoxicity when they received antivenom, 31 developed neurotoxicity. sfEMG in 27 patients with neurotoxicity and 23 without had slightly elevated median jitter on day 1 compared to 29 normal subjects but normalised thereafter. Neurological features resolved in 80% of patients by day 3 with ptosis and weak eye movements resolving last. No clinical or neurophysiological abnormality was detected at 6 weeks or 6 months.

CONCLUSION

Sri Lankan Russell's viper envenoming causes mild neuromuscular dysfunction with no long-term effects. Indian polyvalent antivenom effectively binds free venom in blood but does not reverse neurotoxicity.

Adverse reactions to snake antivenom, and their prevention and treatment

Antivenom is the mainstay of treatment of snakebite envenoming. However, adverse reactions to snake antivenom that is available are common in many parts of the world where snakebite is prevalent. Both acute (anaphylactic or pyrogenic) and delayed (serum sickness type) reactions occur. Acute reactions are usually mild but severe systemic anaphylaxis may develop, often within an hour or so of exposure to antivenom. Serum sickness after antivenom has a delayed onset between 5 and 14 days after its administration. Ultimately, the prevention reactions will depend mainly on improving the quality of antivenom. Until these overdue improvements take place, doctors will have to depend on pharmacological prophylaxis, where the search for the best prophylactic agent is still on-going, as well as careful observation of patients receiving antivenom in preparation for prompt management of acute as well as delayed reactions when they occur.

Benefits of using heterologous polyclonal antibodies and potential applications to new and undertreated infectious pathogens

BACKGROUND

Passive immunotherapy using polyclonal antibodies (immunoglobulins) has been used for over a century in the treatment and post-exposure prophylaxis of various infections and toxins. Heterologous polyclonal antibodies are obtained from animals hyperimmunised with a pathogen or toxin.

AIMS

The aims of this review are to examine the history of animal polyclonal antibody therapy use, their development into safe and effective products and the potential application to humans for emerging and neglected infectious diseases.

METHODS

A literature search of OVID Medline and OVID Embase databases was undertaken to identify articles on the safety, efficacy and ongoing development of polyclonal antibodies. The search contained database-specific MeSH and EMTREE terms in combination with pertinent text-words: polyclonal antibodies and rare/neglected diseases, antivenins, immunoglobulins, serum sickness, anaphylaxis, drug safety, post marketing surveillance, rabies, human influenza, Dengue, West Nile, Nipah, Hendra, Marburg, MERS, Hemorrhagic Fever Virus, and Crimean-Congo. No language limits were applied. The final search was completed on 20.06.2015. Of 1960 articles, title searches excluded many irrelevant articles, yielding 303 articles read in full. Of these, 179 are referenced in this study.

RESULTS

Serum therapy was first used in the 1890s against diphtheria. Early preparation techniques yielded products contaminated with reactogenic animal proteins. The introduction of enzymatic digestion, and purification techniques substantially improved their safety profile. The removal of the Fc fragment of antibodies further reduces hypersensitivity reactions. Clinical studies have demonstrated the efficacy of polyclonal antibodies against various infections, toxins and venoms. Products are being developed against infections for which prophylactic and therapeutic options are currently limited, such as avian influenza, Ebola and other zoonotic viruses.

CONCLUSIONS

Polyclonal antibodies have been successfully applied to rabies, envenomation and intoxication. Polyclonal production provides an exciting opportunity to revolutionise the prognosis of both longstanding neglected tropical diseases as well as emerging infectious threats to humans.

Snake antivenom for snake venom induced consumption coagulopathy

BACKGROUND

Snake venom induced consumption coagulopathy is a major systemic effect of envenoming. Observational studies suggest that antivenom improves outcomes for venom induced consumption coagulopathy in some snakebites and not others. However, the effectiveness of snake antivenom in all cases of venom induced consumption coagulopathy is controversial.

OBJECTIVES

To assess the effect of snake antivenom as a treatment for venom induced consumption coagulopathy in people with snake bite.

SEARCH METHODS

The search was done on 30 January 2015. We searched the Cochrane Injuries Group's Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library), Ovid MEDLINE(R), Ovid MEDLINE(R) In-Process & Other Non-Indexed Citations, Ovid MEDLINE(R) Daily and Ovid OLDMEDLINE(R), Embase Classic+Embase (OvidSP), three other sources, clinical trials registers, and we also screened reference lists.

SELECTION CRITERIA

All completed, published or unpublished, randomised, controlled trials with a placebo or no treatment arm, where snake antivenom was administered for venom induced consumption coagulopathy in humans with snake bites.

DATA COLLECTION AND ANALYSIS

Two authors reviewed the identified trials and independently applied the selection criteria.

MAIN RESULTS

No studies met the inclusion criteria for this review.

AUTHORS' CONCLUSIONS

Randomised placebo-controlled trials are required to investigate the effectiveness of snake antivenom for clinically relevant outcomes in patients with venom induced consumption coagulopathy resulting from snake bite. Although ethically difficult, the routine administration of a treatment that has a significant risk of anaphylaxis cannot continue without strong evidence of benefit.

Protective effect of Euphorbia hirta and its components against snake venom induced lethality

ETHNOPHARMACOLOGICAL RELEVANCE

Despite the use of snake anti-venom therapy, herbal medicine is still in practice to treat snakebites. Euphorbia hirta is traditionally used as antidote for snakebites and also for numerous other ailments. However, the scientific evidence for its anti-snake venom property is still lacking.

MATERIALS AND METHODS

Methanolic extract of E. hirta was evaluated for anti-venom activity under in vitro and ex vivo conditions. Histopathological changes in the vital organs of the mice were also monitored. UHPLC-SRM/MS was used to estimate the phenolic constituents whereas GC-MS analysis was performed to analyze the volatile metabolites present. The major compound was further evaluated for its contribution to the overall inhibitory potential of the extract.

RESULTS

Methanolic extract of E. hirta completely inhibited the venom enzymes under in vitro and reduced the edema ratio. The extract increased the survival time (>24h) of mice which was further evidenced by histopathological analysis of vital organs. Phytochemical analysis revealed higher content of phenolic (144 mg/g extract) compounds in the extract. UHPLC-SRM/MS demonstrated that ellagic acid, gallic acid and quinic acid are the major phenolics whereas GC-MS analysis revealed pyrogallol as the major constituent (60.07%) among the volatile components of the extract. It was also shown that pyrogallol has the ability to differentially inhibit venom protease but not phospholipase A2.

CONCLUSION

The present study confirmed that E. hirta methanolic extract was able to completely inhibit Naja naja venom induced toxicity under in vitro as well as ex vivo conditions, thus providing scientific evidence to its traditional use.

The Effect of a Polyvalent Antivenom on the Serum Venom Antigen Levels of Naja sputatrix (Javan Spitting Cobra) Venom in Experimentally Envenomed Rabbits

The treatment protocol of antivenom in snake envenomation remains largely empirical, partly due to the insufficient knowledge of the pharmacokinetics of snake venoms and the effects of antivenoms on the blood venom levels in victims. In this study, we investigated the effect of a polyvalent antivenom on the serum venom antigen levels of Naja sputatrix (Javan spitting cobra) venom in experimentally envenomed rabbits. Intravenous infusion of 4 ml of Neuro Polyvalent Snake Antivenom [NPAV, F(ab')2 ] at 1 hr after envenomation caused a sharp decline of the serum venom antigen levels, followed by transient resurgence an hour later. The venom antigen resurgence was unlikely to be due to the mismatch of pharmacokinetics between the F(ab')2 and venom antigens, as the terminal half-life and volume of distribution of the F(ab')2 in serum were comparable to that of venom antigens (p > 0.05). Infusion of an additional 2 ml of NPAV was able to prevent resurgence of the serum venom antigen level, resulting in a substantial decrease (67.1%) of the total amount of circulating venom antigens over time course of envenomation. Our results showed that the neutralization potency of NPAV determined by neutralization assay in mice may not be an adequate indicator of its capability to modulate venom kinetics in relation to its in vivo efficacy to neutralize venom toxicity. The findings also support the recommendation of giving high initial dose of NPAV in cobra envenomation, with repeated doses as clinically indicated in the presence of rebound antigenemia and symptom recurrence.

Detection of venom after antivenom administration is largely due to bound venom

Detection of recurrent venom post-antivenom in snake envenoming is commonly reported and thought to be due to insufficient antivenom. However, relatively few reports of recurrence have venom measurement, and in most cases patients clinically improve, despite venom detected post-antivenom. We hypothesized that persistent or recurrent venom detection post-antivenom is due to detecting bound venom. Multiple (>4) serum samples were available from 255 Russell's viper (Daboia russelii) envenomed patients. Enzyme-linked immunosorbent assay was used to measure venom, antivenom and venom-antivenom (VAV) complexes. In 79/255 (31%) there was persistent/recurrent venom detected despite antivenom being present. In these post-antivenom samples, VAV was also detected at the same time as venom was detected. Anti-horse (aH) antiserum was bound to UltraLink (UL) resin and added to in vitro venom-antivenom mixtures, and 15 pre- and post-antivenom samples from patients. There was significantly less free venom detected in in vitro venom-antivenom mixtures to which ULaH had been added compared to those without ULaH added. In 9 post-antivenom patient samples the addition of ULaH reduced venom detected by a median of 80% (69%-88%) compared to only 20% in four pre-antivenom samples. This suggests that the detection of persistent/recurrent venom post-antivenom is due to bound and not free venom.

Hematologic effects and complications of snake envenoming

Hematologic abnormalities are the most common effects of snake envenoming globally. Venom-induced consumption coagulopathy (VICC) is the commonest and most important. Other hematologic abnormalities are an anticoagulant coagulopathy and thrombotic microangiopathy. Venom-induced consumption coagulopathy is a venom-induced activation of the clotting pathway by procoagulant toxins, resulting in clotting factor consumption and coagulopathy. The type of procoagulant toxin differs between snakes and can activate prothrombin, factor X, and factor V or consume fibrinogen. The most useful investigation in VICC is a prothrombin time/international normalized ratio. The d-dimer may assist in early diagnosis, but fibrinogen levels often add little in the clinical setting. Bedside investigations would be ideal, but point-of-care testing international normalized ratio and whole blood clotting tests have been shown to be unreliable in VICC. The major complication of VICC is hemorrhage, including intracranial hemorrhage which is often fatal. The role of antivenom in VICC is controversial and may only be beneficial for some types of snakes including Echis spp where the duration of abnormal clotting is reduced from more than a week to 24 to 48 hours. In contrast, antivenom does not appear to speed the recovery of VICC in Australian snake envenoming. Other treatments for VICC include factor replacement, observation and prevention of trauma, and heparin. An Australian study showed that fresh-frozen plasma speeds recovery of VICC, but early use may increase consumption. There is no evidence to support heparin.

Detection of venom after antivenom is not associated with persistent coagulopathy in a prospective cohort of Russell's viper (Daboia russelii) envenomings

BACKGROUND

Venom recurrence or persistence in the circulation after antivenom treatment has been documented many times in viper envenoming. However, it has not been associated with clinical recurrence for many snakes, including Russell's viper (Daboia spp.). We compare the recovery of coagulopathy to the recurrence or persistence of venom in patients with Russell's viper envenoming.

METHODOLOGY/PRINCIPAL FINDINGS

The study included patients with Russell's viper (D. russelii) envenoming presenting over a 30 month period who had Russell's viper venom detected by enzyme immunoassay. Demographics, information on the snake bite, and clinical effects were collected for all patients. All patients had serum collected for venom specific enzyme immunoassay and citrate plasma to measure fibrinogen levels and prothrombin time (international normalised ratio; INR). Patients with venom recurrence/persistence were compared to those with no detectable recurrence of venom. There were 55 patients with confirmed Russell's viper envenoming and coagulopathy with low fibrinogen concentrations: 31 with venom recurrence/persistence, and 24 with no venom detected post-antivenom. Fibrinogen concentrations increased and INR decreased after antivenom in both the recurrence and non-recurrence patients. Clinical features, laboratory parameters, antivenom dose and length of hospital were similar for both groups. Pre-antivenom venom concentrations were higher in patients with venom recurrence/persistence with a median venom concentration of 385 ng/mL (16-1521 ng/mL) compared to 128 ng/mL (14-1492 ng/mL; p = 0.008).

CONCLUSION

Recurrence of Russell's viper venom was not associated with a recurrence of coagulopathy and length of hospital stay. Further work is required to determine if the detection of venom recurrence is due to the venom specific enzyme immunoassay detecting both venom-antivenom complexes as well as free venom.

Comparison of F(ab')2 versus Fab antivenom for pit viper envenomation: a prospective, blinded, multicenter, randomized clinical trial

Background. Crotalidae Polyvalent Immune Fab (Ovine) has been the only antivenom commercially available in the US since 2007 for treatment of Crotalinae envenomation. Late coagulopathy can occur or recur after clearance of Fab antivenom, often after hospital discharge, lasting in some cases more than 2 weeks. There have been serious, even fatal, bleeding complications associated with recurrence phenomena. Frequent follow-up is required, and additional intervention or hospitalization is often necessary. F(ab')₂ immunoglobulin derivatives have longer plasma half life than do Fab. We hypothesized that F(ab')₂ antivenom would be superior to Fab in the prevention of late coagulopathy following treatment of patients with Crotalinae envenomation. Methods. We conducted a prospective, double-blind, randomized clinical trial, comparing late coagulopathy in snakebitten patients treated with F(ab')₂ with maintenance doses [F(ab')₂/F(ab')₂], or F(ab')₂ with placebo maintenance doses [F(ab')₂/placebo], versus Fab with maintenance doses [Fab/Fab]. The primary efficacy endpoint was coagulopathy (platelet count < 150 K/mm³, fibrinogen level < 150 mg/dL) between end of maintenance dosing and day 8. Results. 121 patients were randomized at 18 clinical sites and received at least one dose of study drug. 114 completed the study. Of these, 11/37 (29.7%) in the Fab/Fab cohort experienced late coagulopathy versus 4/39 (10.3%, p < 0.05) in the F(ab')₂/F(ab')₂ cohort and 2/38 (5.3%, p < 0.05) in the F(ab')₂/placebo cohort. The lowest heterologous protein exposure was with F(ab')₂/placebo. No serious adverse events were related to study drug. In each study arm, one patient experienced an acute serum reaction and one experienced serum sickness. Conclusions. In this study, management of coagulopathic Crotalinae envenomation with longer-half-life F(ab')₂ antivenom, with or without maintenance dosing, reduced the risk of subacute coagulopathy and bleeding following treatment of envenomation.

Current treatment for venom-induced consumption coagulopathy resulting from snakebite

Venomous snakebite is considered the single most important cause of human injury from venomous animals worldwide. Coagulopathy is one of the commonest important systemic clinical syndromes and can be complicated by serious and life-threatening haemorrhage. Venom-induced consumption coagulopathy (VICC) is the commonest coagulopathy resulting from snakebite and occurs in envenoming by Viperid snakes, certain elapids, including Australian elapids, and a few Colubrid (rear fang) snakes. Procoagulant toxins activate the clotting pathway, causing a broad range of factor deficiencies depending on the particular procoagulant toxin in the snake venom. Diagnosis and monitoring of coagulopathy is problematic, particularly in resource-poor countries where further research is required to develop more reliable, cheap clotting tests. MEDLINE and EMBASE up to September 2013 were searched to identify clinical studies of snake envenoming with VICC. The UniPort database was searched for coagulant snake toxins. Despite preclinical studies demonstrating antivenom binding toxins (efficacy), there was less evidence to support clinical effectiveness of antivenom for VICC. There were no placebo-controlled trials of antivenom for VICC. There were 25 randomised comparative trials of antivenom for VICC, which compared two different antivenoms (ten studies), three different antivenoms (four), two or three different doses or repeat doses of antivenom (five), heparin treatment and antivenom (five), and intravenous immunoglobulin treatment and antivenom (one). There were 13 studies that compared two groups in which there was no randomisation, including studies with historical controls. There have been numerous observational studies of antivenom in VICC but with no comparison group. Most of the controlled trials were small, did not use the same method for assessing coagulopathy, varied the dose of antivenom, and did not provide complete details of the study design (primary outcomes, randomisation, and allocation concealment). Non-randomised trials including comparison groups without antivenom showed that antivenom was effective for some snakes (e.g., Echis), but not others (e.g., Australasian elapids). Antivenom is the major treatment for VICC, but there is currently little high-quality evidence to support effectiveness. Antivenom is not risk free, and adverse reactions can be quite common and potentially severe. Studies of heparin did not demonstrate it improved outcomes in VICC. Fresh frozen plasma appeared to speed the recovery of coagulopathy and should be considered in bleeding patients.

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

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

Neurotoxicity in snakebite--the limits of our knowledge

Snakebite is classified by the WHO as a neglected tropical disease. Envenoming is a significant public health problem in tropical and subtropical regions. Neurotoxicity is a key feature of some envenomings, and there are many unanswered questions regarding this manifestation. Acute neuromuscular weakness with respiratory involvement is the most clinically important neurotoxic effect. Data is limited on the many other acute neurotoxic manifestations, and especially delayed neurotoxicity. Symptom evolution and recovery, patterns of weakness, respiratory involvement, and response to antivenom and acetyl cholinesterase inhibitors are variable, and seem to depend on the snake species, type of neurotoxicity, and geographical variations. Recent data have challenged the traditional concepts of neurotoxicity in snake envenoming, and highlight the rich diversity of snake neurotoxins. A uniform system of classification of the pattern of neuromuscular weakness and models for predicting type of toxicity and development of respiratory weakness are still lacking, and would greatly aid clinical decision making and future research. This review attempts to update the reader on the current state of knowledge regarding this important issue.

Pathogenic mechanisms underlying adverse reactions induced by intravenous administration of snake antivenoms

Snake antivenoms are formulations of immunoglobulins, or immunoglobulin fragments, purified from the plasma of animals immunized with snake venoms. Their therapeutic success lies in their ability to mitigate the progress of toxic effects induced by snake venom components, when administered intravenously. However, due to diverse factors, such as deficient manufacturing practices, physicochemical characteristics of formulations, or inherent properties of heterologous immunoglobulins, antivenoms can induce undesirable adverse reactions. Based on the time lapse between antivenom administration and the onset of clinical manifestations, the World Health Organization has classified these adverse reactions as: 1 - Early reactions, if they occur within the first hours after antivenom infusion, or 2 - late reactions, when occurring between 5 and 20 days after treatment. While all late reactions are mediated by IgM or IgG antibodies raised in the patient against antivenom proteins, and the consequent formation of immune complexes, several mechanisms may be responsible for the early reactions, such as pyrogenic reactions, IgE-mediated reactions, or non IgE-mediated reactions. This work reviews the hypotheses that have been proposed to explain the mechanisms involved in these adverse reactions to antivenoms. The understanding of these pathogenic mechanisms is necessary for the development of safer products and for the improvement of snakebite envenomation treatment.

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.

Acute myocardial infarction following a possible direct intravenous bite of Russell's viper (Daboia russelli)

BACKGROUND

Russell's viper (Daboia russelli) bites lead to high morbidity and mortality in South Asia. Although variety of clinical manifestations is reported in viper bite victims, myocardial ischemic events are rare.

CASE PRESENTATION

We report a unique case of inferior wall ST elevation myocardial infarction due to a Russell's viper bite over a vein with possible direct intravenous envenoming, in a young male with no past history or family history suggestive of ischemic cardiac disease, from Sri Lanka. In addition, the possible mechanisms of myocardial ischemia in snake bite victims are also briefly discussed.

CONCLUSION

Importance of the awareness of physicians on the rare, yet fatal manifestations of snake envenoming is highlighted.

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

Background

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

Methods and Findings

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

Conclusions

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

Trial Registration

www.slctr.lk SLCTR/2007/005

Parallels between Russell's viper (Daboia russelii) and hump-nosed viper (Hypnale species) bites in the central hills of Sri Lanka amidst the heavy burden of unidentified snake bites

OBJECTIVE

To describe the epidemiology of snake bite in the region and attempt to compare proven Russell's viper with hump-nosed viper bites.

METHODS

All snake bite admissions to the Toxicology Unit of Teaching Hospital Peradeniya over three year from 2006 were included.

RESULTS

Of the 776 snakebites, 665(86%) were unidentified and non-envenomed. Hump-nosed viper and Russell's viper accounted for 55(7%) and 40(5%) bites respectively, of them, incriminated snakes were found in 36(65%) and 19(48%) cases. The cobra bites-5, krait bites-0. The median ages: Russell's viper bites-41(range 16-66), hump-nosed viper bites-42(range 15-75). The gender incidence, time of bite (>58% daytime) were similar. In hump-nosed viper bite; upper limb involved in 13(36%), happened at home garden in 22(61%), none in paddy fields. In Russell's viper bite; 6(33%) occurred in paddy fields. Dry bites were similar at 5%. In hump-nosed viper bite: local effects 94%, coagulopathy 3%, acute renal failure 3% and one patient died. In Russell's viper bite; local effects 84%, coagulopathy 53%, neurotoxicity 21%. Abdominal pain occurred only in Russell's viper bites 10(53%).

CONCLUSIONS

Overwhelming numbers of unidentified, non-envenomed snakebites are common in the central hills. Some distinctive differences were observed between Russell's viper and hump-nosed viper bites.

Ending the drought: new strategies for improving the flow of affordable, effective antivenoms in Asia and Africa

The development of snake antivenoms more than a century ago should have heralded effective treatment of the scourge of snakebite envenoming in impoverished, mostly rural populations around the world. That snakebite still exists today, as a widely untreated illness that maims, kills and terrifies men, women and children in vulnerable communities, is a cruel anachronism. Antivenom can be an effective, safe and affordable treatment for snakebites, but apathy, inaction and the politicisation of public health have marginalised both the problem (making snakebite arguably the most neglected of all neglected tropical diseases) and its solution. For lack of any coordinated approach, provision of antivenoms has been pushed off the public health agenda, leading to an incongruous decline in demand for these crucial antidotes, excused and fed by new priorities, an absence of epidemiological data, and a poor regulatory framework. These factors facilitated the infiltration of poor quality products that degrade user confidence and undermine legitimate producers. The result is that tens of thousands are denied an essential life-saving medicine, allowing a toll of human suffering that is a summation of many individual catastrophes. No strategy has been developed to address this problem and to overcome the intransigence and inaction responsible for the global tragedy of snakebite. Attempts to engage with the broader public health community through the World Health Organisation (WHO), GAVI, and other agencies have failed. Consequently, the toxinology community has taken on a leadership role in a new approach, the Global Snakebite Initiative, which seeks to mobilise the resources, skills and experience of scientists and clinicians for whom venoms, toxins, antivenoms, snakes and snakebites are already fields of interest. Proteomics is one such discipline, which has embraced the potential of using venoms in bio-discovery and systems biology. The fields of venomics and antivenomics have recently evolved from this discipline, offering fresh hope for the victims of snakebites by providing an exciting insight into the complexities, nature, fundamental properties and significance of venom constituents. Such a rational approach brings with it the potential to design new immunising mixtures from which to raise potent antivenoms with wider therapeutic ranges. This addresses a major practical limitation in antivenom use recognised since the beginning of the 20th century: the restriction of therapeutic effectiveness to the specific venom immunogen used in production. Antivenomic techniques enable the interactions between venoms and antivenoms to be examined in detail, and if combined with functional assays of specific activity and followed up by clinical trials of effectiveness and safety, can be powerful tools with which to evaluate the suitability of current and new antivenoms for meeting urgent regional needs. We propose two mechanisms through which the Global Snakebite Initiative might seek to end the antivenom drought in Africa and Asia: first by establishing a multidisciplinary, multicentre, international collaboration to evaluate currently available antivenoms against the venoms of medically important snakes from specific nations in Africa and Asia using a combination of proteomic, antivenomic and WHO-endorsed preclinical assessment protocols, to provide a validated evidence base for either recommending or rejecting individual products; and secondly by bringing the power of proteomics to bear on the design of new immunising mixtures to raise Pan-African and Pan-Asian polyvalent antivenoms of improved potency and quality. These products will be subject to rigorous clinical assessment. We propose radically to change the basis upon which antivenoms are produced and supplied for the developing world. Donor funding and strategic public health alliances will be sought to make it possible not only to sustain the financial viability of antivenom production partnerships, but also to ensure that patients are relieved of the costs of antivenom so that poverty is no longer a barrier to the treatment of this important, but grossly neglected public health emergency.

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

BACKGROUND

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

METHODS AND FINDINGS

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

CONCLUSIONS

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

Coated cross-species antibodies by mannosamine-biotin adduct confer protection against snake venom without eliciting humoral immune response

Passive immunization with cross-species antibodies triggers the patient's immune response, thereby preventing repeated treatment. Mannosamine-biotin adduct (MBA) has been described as a masking agent for immunogenic reduction and here, the immunogenicity and biological activity of MBA-coated horse anti-viper venom (hsIgG) were compared to those of uncoated or PEGylated hsIgG. In in vitro tests, hsIgG binding was not affected by MBA conjugation. The immune response to hsIgG-MBA was about 8-fold and 32-fold lower than to PEG-coated and uncoated hsIgG, respectively. In vivo, hsIgG-MBA showed efficient venom-neutralization activity. We thus demonstrate the feasibility of using MBA as a masking agent for passive immunization with cross-species antibodies.