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

Haemotoxic snake venoms: their functional activity, impact on snakebite victims and pharmaceutical promise

Snake venoms are mixtures of numerous proteinacious components that exert diverse functional activities on a variety of physiological targets. Because the toxic constituents found in venom vary from species to species, snakebite victims can present with a variety of life-threatening pathologies related to the neurotoxic, cytotoxic and haemotoxic effects of venom. Of the 1·8 million people envenomed by snakes every year, up to 125 000 die, while hundreds of thousands survive only to suffer with life-changing long-term morbidity. Consequently, snakebite is one of the world's most severe neglected tropical diseases. Many snake venoms exhibit strong haemotoxic properties by interfering with blood pressure, clotting factors and platelets, and by directly causing haemorrhage. In this review we provide an overview of the functional activities of haemotoxic venom proteins, the pathologies they cause in snakebite victims and how their exquisite selectivity and potency make them amenable for use as therapeutic and diagnostic tools relevant for human medicine.

Peptidomimetic hydroxamate metalloproteinase inhibitors abrogate local and systemic toxicity induced by Echis ocellatus (saw-scaled) snake venom

The ability of two peptidomimetic hydroxamate metalloproteinase inhibitors, Batimastat and Marimastat, to abrogate toxic and proteinase activities of the venom of Echis ocellatus from Cameroon and Ghana was assessed. Since this venom largely relies for its toxicity on the action of zinc-dependent metalloproteinases (SVMPs), the hypothesis was raised that toxicity could be largely eliminated by using SVMP inhibitors. Both hydroxamate molecules inhibited local and pulmonary hemorrhagic, in vitro coagulant, defibrinogenating, and proteinase activities of the venoms in conditions in which venom and inhibitors were incubated prior to the test. In addition, the inhibitors prolonged the time of death of mice receiving 4 LD₅₀s of venom by the intravenous route. Lower values of IC₅₀ were observed for in vitro and local hemorrhagic activities than for systemic effects. When experiments were performed in conditions that simulated the actual circumstances of snakebite, i.e. by administering the inhibitor after envenoming, Batimastat completely abrogated local hemorrhage if injected immediately after venom. Moreover, it was also effective at inhibiting lethality and defibrinogenation when venom and inhibitor were injected by the intraperitoneal route. Results suggest that these, and possibly other, metalloproteinase inhibitors may become an effective adjunct therapy in envenomings by E. ocellatus when administered at the anatomic site of venom injection rapidly after the bite.

Preclinical evaluation of three polyspecific antivenoms against the venom of Echis ocellatus: Neutralization of toxic activities and antivenomics

Snakebite envenoming has a heavy burden in the public health in sub-Saharan Africa. The viperid species Echis ocellatus (carpet viper or saw-scaled viper) is the medically most important snake in the savannahs of western sub-Saharan Africa. Several antivenoms are being distributed and used in this region for the treatment of envenomings by E. ocellatus, but the preclinical efficacy of some of these antivenoms has not been assessed. The present study evaluated the preclinical efficacy against E. ocellatus venom of three polyspecific antivenoms: (a) Snake Venom Antiserum (Pan Africa), manufactured by Premium Serums and Vaccines (India); (b) Snake Venom Antiserum (Africa), manufactured by VINS Bioproducts (India); and (c) Antivipmyn(®) Africa, manufactured by Instituto Bioclon (Mexico). Antivenomics analysis revealed the ability of the three antivenoms to immunocapture the majority of components of the venoms of E. ocellatus from Cameroon, Nigeria and Mali, although their maximal immunocapturing capability varied. Bioclon and Premium Serums antivenoms were effective in the neutralization of lethal, hemorrhagic and in vitro coagulant activities of the venom of E. ocellatus from Cameroon, albeit with different potencies. VINS antivenom neutralized hemorrhagic activity of this venom, but failed to neutralize lethality at the highest antivenom dose tested, and had a low neutralizing efficacy against in vitro coagulant effect.

Efficacy of Indian polyvalent snake antivenoms against Sri Lankan snake venoms: lethality studies or clinically focussed in vitro studies

In vitro antivenom efficacy studies were compared to rodent lethality studies to test two Indian snake antivenoms (VINS and BHARAT) against four Sri Lankan snakes. In vitro efficacy was tested at venom concentrations consistent with human envenoming. Efficacy was compared statistically for one batch from each manufacturer where multiple vials were available. In binding studies EC50 for all VINS antivenoms were less than BHARAT for D. russelii [553 μg/mL vs. 1371 μg/mL;p = 0.016), but were greater for VINS antivenoms compared to BHARAT for N. naja [336 μg/mL vs. 70 μg/mL;p < 0.0001]. EC50 of both antivenoms was only slighty different for E. carinatus and B. caeruleus. For procoagulant activity neutralisation, the EC50 was lower for VINS compared to BHARAT - 60 μg/mL vs. 176 μg/mL (p < 0.0001) for Russell's viper and 357 μg/mL vs. 6906μg/mL (p < 0.0001) for Saw-scaled viper. Only VINS antivenom neutralized in vitro neurotoxicity of krait venom. Both antivenoms partially neutralized cobra and didn't neutralize Russell's viper neurotoxicity. Lethality studies found no statistically significant difference in ED50 values between VINS and BHARAT antivenoms. VINS antivenoms appeared superior to BHARAT at concentrations equivalent to administering 10 vials antivenom, based on binding and neutralisation studies. Lethality studies were inconsistent suggesting rodent death may not measure relevant efficacy outcomes in humans.

Cost-Effectiveness of Antivenoms for Snakebite Envenoming in 16 Countries in West Africa

Background

Snakebite poisoning is a significant medical problem in agricultural societies in Sub Saharan Africa. Antivenom (AV) is the standard treatment, and we assessed the cost-effectiveness of making it available in 16 countries in West Africa.

Methods

We determined the cost-effectiveness of AV based on a decision-tree model from a public payer perspective. Specific AVs included in the model were Antivipmyn, FAV Afrique, EchiTab-G and EchiTab-Plus. We derived inputs from the literature which included: type of snakes causing bites (carpet viper (Echis species)/non-carpet viper), AV effectiveness against death, mortality without AV, probability of Early Adverse Reactions (EAR), likelihood of death from EAR, average age at envenomation in years, anticipated remaining life span and likelihood of amputation. Costs incurred by the victims include: costs of confirming and evaluating envenomation, AV acquisition, routine care, AV transportation logistics, hospital admission and related transportation costs, management of AV EAR compared to the alternative of free snakebite care with ineffective or no AV. Incremental Cost Effectiveness Ratios (ICERs) were assessed as the cost per death averted and the cost per Disability-Adjusted-Life-Years (DALY) averted. Probabilistic Sensitivity Analyses (PSA) using Monte Carlo simulations were used to obtain 95% Confidence Intervals of ICERs.

Results

The cost/death averted for the 16 countries of interest ranged from $1,997 in Guinea Bissau to $6,205 for Liberia and Sierra Leone. The cost/DALY averted ranged from $83 (95% Confidence Interval: $36-$240) for Benin Republic to $281 ($159–457) for Sierra-Leone. In all cases, the base-case cost/DALY averted estimate fell below the commonly accepted threshold of one time per capita GDP, suggesting that AV is highly cost-effective for the treatment of snakebite in all 16 WA countries. The findings were consistent even with variations of inputs in 1—way sensitivity analyses. In addition, the PSA showed that in the majority of iterations ranging from 97.3% in Liberia to 100% in Cameroun, Guinea Bissau, Mali, Nigeria and Senegal, our model results yielded an ICER that fell below the threshold of one time per capita GDP, thus, indicating a high degree of confidence in our results.

Conclusions

Therapy for SBE with AV in countries of WA is highly cost-effective at commonly accepted thresholds. Broadening access to effective AVs in rural communities in West Africa is a priority.

Antivenom is the main intervention against snakebite poisoning but is relatively scarce, unaffordable and the situation has been compounded further by the recent cessation of production of effective antivenoms and marketing of inappropriate products. Given this crisis, we assessed the cost effectiveness of providing antivenoms in West Africa by comparing costs associated with antivenom treatment against their health benefits in decreasing mortality. In the most comprehensive analyses ever conducted, it was observed the incremental cost effectiveness ratio of providing antivenom ranged from $1,997 in Guinea Bissau to $6,205 for Liberia and Sierra-Leone per death averted while cost per Disability Adjusted Life Year (DALY) averted ranged from $83 for Benin Republic to $281 for Sierra-Leone. There is probability of 97.3–100% that antivenoms are very cost-effective in the analyses. These demonstrate antivenom is highly cost-effective and compares favorably to other commonly funded healthcare interventions. Providing and broadening antivenom access throughout areas at risk in rural West Africa should be prioritized given the considerable reduction in deaths and DALYs that could be derived at a relatively small cost.

Prospective, consecutive case series of 158 snakebite patients treated at Savannakhet provincial hospital, Lao People's Democratic Republic with high incidence of anaphylactic shock to horse derived F(ab')2 antivenom

Snakebites are a seriously neglected public health problem in Lao PDR. Community-based cross-sectional surveys in two districts of Savannakhet province in Southern Laos revealed an incidence of up to 1105 snakebites per 100,000 persons per year. In contrast the number of snakebite patients treated in district and provincial hospitals are low. In order to improve health care for snakebite victims, antivenom was introduced to Savannakhet provincial hospital in July 2013 and medical staff has been trained in management of venomous snakebites at the same time. After the intervention the number of snakebite patients treated at the provincial hospital increased significantly from 4 patients in 2012 to 158 snakebite patients between July 2013 and November 2015. They were included into a prospective, consecutive case series. Median age was 32 years (range 1.5-70 years) and male-to-female ratio 2.2:1. Forty patients were bitten by Malayan pit vipers, 26 by green pit vipers, 24 by cobras, including 3 cases of venom ophthalmia, 5 by kraits, 8 by non-venomous species and in 55 cases the snake could not be identified. Forty-three out of 158 patients received horse derived F(ab')2 antivenom from Queen Saovabha Memorial Institute (QSMI) in Bangkok. Twenty-three patients (53%) developed early adverse reactions (EARs) within one hour after antivenom administration, including 13 patients (30%) with severe anaphylaxis. This extremely high rate of severe EARs turns the use of antivenom into a risky intervention. In contrast a retrospective chart review from Chulalongkorn University in Bangkok found only 3.5% early reactions including 1.2% severe anaphylactic reactions using the same antivenom from QSMI between 1997 and 2006. The reason for this enormous difference remains unclear. A better understanding of the aetiology and pathophysiology behind antivenom induced anaphylaxis is crucial in order to identify patients at risk and to improve safety of antivenom administration.

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.

Understanding and confronting snakebite envenoming: The harvest of cooperation

During 45 years, the Instituto Clodomiro Picado (ICP, University of Costa Rica) has developed an ambitious scientific, technological, productive, and social program aimed at providing a better understanding of snakes and their venoms, contributing to the development, production and distribution of antivenoms, improving the prevention and management of snakebite envenomings, and strengthening human resources in science and technology. Among other topics, its research agenda has focused on the local tissue alterations induced by viperid snake venoms, i.e. myonecrosis, hemorrhage, dermonecrosis, extracellular matrix degradation, lymphatic vessel damage, and inflammation. In addition, the preclinical efficacy of antivenoms has been thoroughly investigated, together with the technological development of novel antivenoms. ICP's project has been based on a philosophical frame characterized by: (a) An integrated approach for confronting the problem of snakebites, involving research, production, extension activities, and teaching; (b) a cooperative and team work perspective in the pursuit of scientific, technological, productive, and social goals; (c) a search for excellence and continuous improvement in the quality of its activities; and (d) a vision of solidarity and compassion, based on the realization that snakebite envenomings mostly affect impoverished vulnerable populations in the rural settings of developing countries. A key aspect in this program has been the consolidation of international partnerships with groups of all continents, within a frame of academic and social cooperation, some of which are described in this review.

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

CONTEXT

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

OBJECTIVE

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

MATERIALS AND METHODS

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

RESULTS

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

DISCUSSION

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

CONCLUSION

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

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.

High-dose versus low-dose antivenom in the treatment of poisonous snake bites: A systematic review

Though snake antivenom (SAV) is the mainstay of therapy for poisonous snake bites, there is no universally accepted standard regimen regarding the optimum dose (low vs. high). We therefore, undertook this systematic review to address this important research question. We searched all the published literature through the major electronic databases till August 2014. Randomized clinical trials (RCTs) were included. Eligible trials compared low versus high dose SAV in poisonous snake bite. The review has been registered at PROSPERO (Registration number: CRD42014009700). Of 36 citations retrieved, a total of 5 RCTs (n = 473) were included in the final analyses. Three trials were open-label, 4 conducted in Indian sub-continent and 1 in Brazil. The doses of SAV varied in the high dose group from 40 ml to 550 ml, and in the low dose group from 20 ml to 220 ml. There was no significant difference between the two groups for any of the outcomes except duration of hospital stay, which was lower in the low dose group. The GRADE evidence generated was of "very low quality." Low-dose SAV is equivalent or may be superior to high-dose SAV in management of poisonous snake bite. Low dose is also highly cost-effective as compared to the high dose. But the GRADE evidence generated was of "very low quality" as most were open label trials. Further trials are needed to make definitive recommendations regarding the dose and these should also include children <9 years of age.

Cost-effectiveness of antivenoms for snakebite envenoming in Nigeria

Background

Snakebite envenoming is a major public health problem throughout the rural tropics. Antivenom is effective in reducing mortality and remains the mainstay of therapy. This study aimed to determine the cost-effectiveness of using effective antivenoms for Snakebite envenoming in Nigeria.

Methodology

Economic analysis was conducted from a public healthcare system perspective. Estimates of model inputs were obtained from the literature. Incremental Cost Effectiveness Ratios (ICERs) were quantified as deaths and Disability-Adjusted-Life-Years (DALY) averted from antivenom therapy. A decision analytic model was developed and analyzed with the following model base-case parameter estimates: type of snakes causing bites, antivenom effectiveness to prevent death, untreated mortality, risk of Early Adverse Reactions (EAR), mortality risk from EAR, mean age at bite and remaining life expectancy, and disability risk (amputation). End-user costs applied included: costs of diagnosing and monitoring envenoming, antivenom drug cost, supportive care, shipping/freezing antivenom, transportation to-and-from hospital and feeding costs while on admission, management of antivenom EAR and free alternative snakebite care for ineffective antivenom.

Principal Findings

We calculated a cost/death averted of ($2330.16) and cost/DALY averted of $99.61 discounted and $56.88 undiscounted. Varying antivenom effectiveness through the 95% confidence interval from 55% to 86% yield a cost/DALY averted of $137.02 to $86.61 respectively. Similarly, varying the prevalence of envenoming caused by carpet viper from 0% to 96% yield a cost/DALY averted of $254.18 to $78.25 respectively. More effective antivenoms and carpet viper envenoming rather than non-carpet viper envenoming were associated with lower cost/DALY averted.

Conclusions/Significance

Treatment of snakebite envenoming in Nigeria is cost-effective with a cost/death averted of $2330.16 and cost/DALY averted of $99.61 discounted, lower than the country's gross domestic product per capita of $1555 (2013). Expanding access to effective antivenoms to larger segments of the Nigerian population should be a considered a priority.

Snake bite is a major public health problem throughout rural communities in West Africa and leads to a significant number of deaths and disabilities per year. Even though effective antivenoms exist against the locally prevalent carpet viper and other poisonous snakes, they are generally not available in community settings, possibly because of their high acquisition cost. We evaluated the cost-effectiveness of making antivenom more broadly available in Nigeria by comparing the treatment costs associated with antivenom therapy against their medical benefit in reducing the risk of mortality. We find that the incremental cost effectiveness ratio (ICER) associated with making antivenom available in Nigeria was $2,330 per death averted and $100 per disability adjusted life year (DALY) averted. Both of these suggest that snakebite antivenom is highly cost-effective in Nigeria and they also compare very favorably against other commonly funded health interventions for which similar estimates exist. Since a substantial reduction in mortality and DALYs could be achieved at a relatively modest upfront cost, expanding access to antivenom to broader parts of the population should be a priority consideration for future investments in healthcare.

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.

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.

Medically important differences in snake venom composition are dictated by distinct postgenomic mechanisms

Variation in venom composition is a ubiquitous phenomenon in snakes and occurs both interspecifically and intraspecifically. Venom variation can have severe outcomes for snakebite victims by rendering the specific antibodies found in antivenoms ineffective against heterologous toxins found in different venoms. The rapid evolutionary expansion of different toxin-encoding gene families in different snake lineages is widely perceived as the main cause of venom variation. However, this view is simplistic and disregards the understudied influence that processes acting on gene transcription and translation may have on the production of the venom proteome. Here, we assess the venom composition of six related viperid snakes and compare interspecific changes in the number of toxin genes, their transcription in the venom gland, and their translation into proteins secreted in venom. Our results reveal that multiple levels of regulation are responsible for generating variation in venom composition between related snake species. We demonstrate that differential levels of toxin transcription, translation, and their posttranslational modification have a substantial impact upon the resulting venom protein mixture. Notably, these processes act to varying extents on different toxin paralogs found in different snakes and are therefore likely to be as important as ancestral gene duplication events for generating compositionally distinct venom proteomes. Our results suggest that these processes may also contribute to altering the toxicity of snake venoms, and we demonstrate how this variability can undermine the treatment of a neglected tropical disease, snakebite.

Diagnosis of snakebite and the importance of immunological tests in venom research

In many cases of envenoming following snake bite, the snake responsible for the accident remains unidentified; this frequently results in difficulty deciding which antivenom to administer to the systemically-envenomed victim, especially when only monospecific antivenoms are available. Normally the specific diagnosis of snake bite can be conveniently made using clinical and laboratory methods. Where clinical diagnosis depends upon the recognition of specific signs of envenoming in the patient, laboratory diagnosis is based on the changes which occur in envenomed victims including the detection of abnormalities in blood parameters, presence/absence of myoglobinuria, changes in certain enzyme levels, presence/absence of neurotoxic signs and the detection in the blood of specific venom antigens using immunologically-based techniques, such as enzyme immunoassay. It is the latter which is the main subject of this review, together with the application of techniques currently used to objectively assess the effectiveness of new and existing antivenoms, to assess first aid measures, to investigate the possible use of such methods in epidemiological studies, and to detect individual venom components. With this in mind, we have discussed in some detail how such techniques were developed and how they have helped in the treatment of envenoming particularly and in venom research in general.

A multicomponent strategy to improve the availability of antivenom for treating snakebite envenoming

Snakebite envenoming is a common but neglected public health problem, particularly in impoverished rural regions of sub-Saharan Africa, Asia and Latin America. The only validated treatment for this condition is passive immunotherapy with safe and effective animal-derived antivenoms. However, there is a long-lasting crisis in the availability of these life-saving medications, particularly in sub-Saharan Africa and parts of Asia. We herein advocate a multicomponent strategy to substantially improve the availability of safe and effective antivenoms at the global level. This strategy is based on: (i) preparing validated collections of representative venom pools from the most medically dangerous snakes in high-risk regions of the world; (ii) strengthening the capacity of national antivenom manufacturing and quality control laboratories and their regulatory authorities and establishing new facilities in developing countries through technology transfer, as an integral part of efforts to develop their biological products industry; (iii) getting established laboratories to generate antivenoms for various regions of the world; and (iv) getting governments and relevant organizations to give snakebite envenoming due recognition within national and international public health policy frameworks. These ways of making antivenom available should be complemented by actions to improve health information systems, the accessibility of antivenoms, the training of medical and nursing staff, and community-based education. Such a multicomponent strategy involving stakeholders on many levels could help consolidate sustainable improvements in antivenom availability worldwide.

Anticomplementary activity of horse IgG and F(ab')2 antivenoms

Envenomation by poisonous animals is a neglected condition according to the World Health Organization (WHO). Antivenoms are included in the WHO Essential Medicines List. It has been assumed that immunoglobulin G (IgG) antivenoms could activate the complement system through Fc and induce early adverse reactions (EARs). However, data in the literature indicate that F(ab')2 fragments can also activate the complement system. Herein, we show that several batches of IgG and F(ab')2 antivenoms from the Butantan, Vital Brazil, and Clodomiro Picado Institutes activated the complement classical pathway and induced the production of C3a; however, only those antivenoms from Clodomiro Picado generated C5a. Different protein profiles (IgG heavy chain, protein contaminants, and aggregates) were observed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analyses. Our results show that various antivenoms from different producers are able to activate the classical pathway of the complement system and generate anaphylatoxins, and these findings suggest that factors, such as composition, contaminant proteins, and aggregates, may influence the anticomplementary activity of antivenoms in vitro. Therefore, there is a need to further improve antivenom production methods to reduce their anticomplementary activity and potential to cause EARs.

Public health aspects of snakebite care in West Africa: perspectives from Nigeria

Snakebite envenoming is a major public health problem among rural communities of the Nigerian savanna. The saw-scaled or carpet viper (Echis ocellatus) and, to a lesser extent, the African cobras (Naja spp.) and puff adders (Bitis arietans) have proved to be the most important cause of mortality and morbidity. The main clinical features of E. ocellatus envenoming are systemic hemorrhage, incoagulable blood, shock, local swelling, bleeding and, occasionally, necrosis. Bites may be complicated by amputation, blindness, disability, disfigurement, mutilation, tissue destruction and psychological consequences. Antivenom remains the hallmark and mainstay of envenoming management while studies in Nigeria confirm its protection of over 80% against mortality from carpet-viper bites. However, the availability, distribution and utilization of antivenom remain challenging although two new antivenoms (monospecific EchiTab G and trispecific EchiTab ICP-Plus) derived from Nigerian snake venoms have proven very effective and safe in clinical trials. A hub-and-spoke strategy is suggested for broadening antivenom access to endemic rural areas together with instituting quality assurance, standardization and manpower training. With the advent of antivenomics, national health authorities must be aided in selecting and purchasing antivenoms appropriate to their national needs while manufacturers should be helped in practical ways to improve the safety, efficacy and potential coverage against snake venoms and pricing of their products.

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.

Factors affecting snakebite mortality in north-eastern Nigeria

Snakebite is an important cause of mortality among rural dwellers in the savannah region of West Africa. We conducted a retrospective review of snakebite patients managed by experienced medical staff at Kaltungo in north-eastern Nigeria to determine the cause of death. During a 36 month period there were 94 deaths among 6687 victims (1.41%). Relative risk (RR) of mortality increased to 2.29 (95% CI 1.35-3.89) during a period when source of antivenom became unreliable. The increase was not due to seasonal variation. In a logistic regression model predictors of mortality were new central nervous system (CNS) features (Odds ratio (OR) = 24.61; 95% CI 6.93-87.41) and delay from bite to hospitalization (OR for every 1 h delay = 1.01; 95% CI 1.00-1.02). Treatment with antivenom was protective (OR = 0.17; 95% CI 0.03-0.96). Relationship of anaemia and shock to mortality were not maintained following adjustment. Effort should be made to provide regionally appropriate, affordable and effective antivenoms in addition to enforcement of continuous regulatory control measures. Antivenoms should be distributed to affected areas and treatment access points of care expanded to communities to diminish travel time. The populations at risk should be educated on avoiding unnecessary delays and on prevention of bites.

Safety of intravenous equine F(ab')2: insights following clinical trials involving 1534 recipients of scorpion antivenom

INTRODUCTION

The technology of antivenom production has gradually changed since the earliest production of antisera around the turn of the 20th century. Use of early antisera was associated with frequent acute adverse reactions and serum sickness. New F(ab')2 products, manufactured using pepsin degradation of immunoglobulin together with precipitation of unwanted protein and albumin serum fractions, should in concept cause fewer immune reactions in clinical use.

METHODS

A linked set of five prospective clinical trials of an equine F(ab')2 antivenom, together with one historical control study, were completed during development of the product for a Biological License Application through the US FDA. Adverse events were recorded and categorized, with particular attention to the frequency of immune reactions.

RESULTS

A total of 1534 patients ages 0.1-90.5 years received antivenom, in Arizona and in Mexico, for treatment of scorpion envenomation. Total dosing ranged from 1 to 5 vials except for one outlier who received 10 vials. Estimated protein exposure was 12-275 mg per patient (outlier, up to 550 mg). Three patients (0.2%) had acute reactions to antivenom infusion (one urticaria, one urticaria and dyspnea, and one panic attack). Eight (0.5%) had rashes suggestive of Type 3 immune reactions, although none had the full syndrome of serum sickness. Two women were treated for envenomation during the first trimester of pregnancy, one of whom subsequently experienced a spontaneous abortion.

CONCLUSIONS

Rates of immune reaction to this product were two orders of magnitude lower than the range (up to 75% for early and 81% for late reactions) historically reported with use of minimally refined whole immunoglobulin products against a variety of infections and envenomations. Lower protein dose, greater purity of the active component, lack of the immunogenic Fc portion of the immunoglobulin molecule, and slow intravenous infusion are likely to be the reason for this. Clinical implications of a safer product include that it can be employed in settings where antivenom was once considered too dangerous to use, such as primary care clinics and remote rural areas.

Medically significant late bleeding after treated crotaline envenomation: a systematic review

STUDY OBJECTIVE

We estimate the proportion of patients with crotaline snake envenomation who are treated with Crotalidae polyvalent immune Fab (ovine) antivenom and who develop medically significant late bleeding.

METHODS

We performed a systematic review of all published cohort studies of North American crotaline snake envenomation patients treated with Fab antivenom. We searched PubMed, Ovid MEDLINE, and EMBASE from January 1, 1997, to April 30, 2012. Data were extracted by 2 trained researchers. Late bleeding was defined as bleeding that began or recurred after initial control of the envenomation syndrome. Medically significant late bleeding was defined a priori as late bleeding treated with RBC transfusion, vasoactive drug infusion, surgery, or rehospitalization or associated with a hemoglobin decrease of greater than or equal to 3 g/dL, hematocrit decrease of greater than or equal to 8%, disability, or death. Summary incidence and 95% confidence intervals (CIs) were calculated with a random-effects Poisson regression model.

RESULTS

Nineteen unique cohort studies were identified. Four studies collected data prospectively, and in 9 studies, patients were followed actively after hospital discharge. A total of 1,017 subjects were enrolled in these cohort studies. Late bleeding was reported in 9 subjects (0.9%; 95% CI 0.4% to 2.2%), of whom 5 subjects (0.5%; 95% CI 0.1% to 1.7%) had medically significant late bleeding. Three patients received RBC transfusion; no deaths or permanent sequelae were reported. Estimates of risk may be affected by underreporting.

CONCLUSION

Medically significant late bleeding appears to be uncommon in snakebite victims treated with Fab antivenom.

Antivenom therapy of carpet viper (Echis ocellatus) envenoming: effectiveness and strategies for delivery in West Africa

In West Africa, response to specific, geographically appropriate, antivenom is often dramatic following carpet viper (Echis ocellatus) envenoming with rapid restoration of blood coagulability and resolution of spontaneous haemorrhage. Envenoming from Australasian snakes causing similar coagulopathies may respond less dramatically and the effectiveness of antivenom is being questioned. Here we have reviewed and re-analysed all published preclinical and clinical studies on envenoming and antivenom therapy conducted in West Africa to determine the effectiveness of antivenom. 22 studies provided relevant information: 12 observational studies, 4 RCTs and 6 preclinical studies. Four comparative studies confirmed statistically significant protection against mortality ranging from 57 to 87% using specific antivenoms compared to non-specific or no antivenoms. Meta-analysis estimated combined Odds Ratio (95% CI) of 0.25 (0.14-0.45) of dying among those treated with specific antivenom or 75% (95% CI: 55-86%) protection against death. Mortality more than doubled during times when stocks of reliable antivenoms ran out, with Relative Risk (95% CI)] of 2.33 (1.26-4.06). Serum kinetics of venom antigen/antivenom levels also confirmed that decline of venom antigen levels coincided with resolution of coagulopathy while decline of antivenom levels was associated with venom antigen reappearance and recurrence of coagulopathy. Preclinical and antivenomics analysis confirmed efficacy of regionally appropriate antivenoms against E. ocellatus and related species' venoms in Sub-Saharan Africa but not against Asian Echis carinatus venom. Antivenoms raised against E. carinatus were ineffective in human studies. In West Africa, specific antivenom is effective in managing carpet viper envenoming. A centralized hub-and-spoke strategy is suggested for broadening antivenom access to endemic rural areas together with instituting quality assurance, standardization and manpower training. Benefits, risks, cost-effectiveness and feasibility of the approach should be formally assessed.

Redi award lecture: clinical studies of snake-bite in four tropical continents

Research is discussed in the areas of venomous snake taxonomy, epidemiology, species diagnosis, defining the clinical phenotype of human envenoming, pathophysiological mechanisms of envenoming, clinical testing of antivenoms and prevention of snake-bite through community education. This work was carried out over the past 40 years in many countries in four tropical continents. The help and friendship of a large number of collaborators is gratefully acknowledged.

Consequences of neglect: analysis of the sub-Saharan African snake antivenom market and the global context

BACKGROUND

The worldwide neglect of immunotherapeutic products for the treatment of snakebite has resulted in a critical paucity of effective, safe and affordable therapy in many Third World countries, particularly in Africa. Snakebite ranks high among the most neglected global health problems, with thousands of untreated victims dying or becoming permanently maimed in developing countries each year because of a lack of antivenom-a treatment that is widely available in most developed countries. This paper analyses the current status of antivenom production for sub-Saharan African countries and provides a snapshot of the global situation.

METHODS

A global survey of snake antivenom products was undertaken in 2007, involving 46 current and former antivenom manufacturers. Companies producing antivenom for use in sub-Saharan Africa were re-surveyed in 2010 and 2011.

RESULTS

The amount of antivenom manufactured for sub-Saharan Africa increased between 2007 and 2010/11, however output and procurement remained far below that required to treat the estimated 300,000-500,000 snakebite victims each year. Variable potency and inappropriate marketing of some antivenoms mean that the number of effective treatments available may be as low as 2.5% of projected needs. Five companies currently market antivenom for sale in Africa; three others have products in the final stages of development; and since 2007 one has ceased production indefinitely. Most current antivenom producers possess a willingness and capacity to raise output. However inconsistent market demand, unpredictable financial investment and inadequate quality control discourage further production and threaten the viability of the antivenom industry.

CONCLUSION

Financial stimulus is urgently needed to identify and develop dependable sources of high-grade antivenoms, support current and emerging manufacturers, and capitalise on existing unutilised production capacity. Investing to ensure a consistent and sustainable marketplace for efficacious antivenom products will drive improvements in quality, output and availability, and save thousands of lives each year.

Improving antivenom availability and accessibility: science, technology, and beyond

Snakebite envenomings constitute a serious and neglected public health problem. Despite the fact that effective treatment exists, i.e. administration of animal-derived antivenoms, the availability and accessibility of these life-saving immunobiologicals is deficitary in various parts of the world, particularly in sub-Saharan Africa and some regions of Asia. This article discusses some of the problems that need to be circumvented in order to improve the availability and accessibility of antivenoms. The conglomerate of antivenom manufacturers is highly heterogeneous in terms of technological base, qualification of staff, implementation of Good Manufacturing Practices (GMPs), and volume of production. Therefore, improvements in antivenom quality and availability should be based on strategies tailored to the situation of each region or country; in this context, three different scenarios are discussed. Accessibility of antivenoms demands concerted efforts at multiple levels, including raising the awareness of public health authorities on the relevance of the problem, implementing innovative antivenom purchasing schemes, strengthening national distribution channels on the basis of robust epidemiological information, improving the cold chain and the provision of health services in remote rural settings, supporting the correct use of antivenoms, and promoting the involvement of local community organizations in various aspects of prevention and management. These tasks should be envisaged in terms of synergistic, interprogrammatic and intersectorial interventions, with the participation of many players.

Efficacy of IgG and F(ab')2 antivenoms to neutralize snake venom-induced local tissue damage as assessed by the proteomic analysis of wound exudate

Proteomic analysis of wound exudates represents a valuable tool to investigate tissue pathology and to assess the therapeutic success of various interventions. In this study, the ability of horse-derived IgG and F(ab')(2) antivenoms to neutralize local pathological effects induced by the venom of the snake Bothrops asper in mouse muscle was investigated by the proteomic analysis of exudates collected in the vicinity of affected tissue. In experiments involving the incubation of venom and antivenom prior to injection in mice, hemorrhagic activity was completely abolished and local muscle-damaging activity was significantly reduced by the antivenoms. In these conditions, the relative amounts of several intracellular and extracellular matrix proteins were reduced by the action of antivenoms, whereas the relative amounts of various plasma proteins were not modified. Because not all intracellular proteins were reduced, it is likely that there is a residual cytotoxicity not neutralized by antivenoms. In experiments designed to more closely reproduce the actual circumstances of envenoming, that is, when antivenom is administered after envenomation, the number of proteins whose amounts in exudates were reduced by antivenoms decreased, underscoring the difficulty in neutralizing local pathology due to the very rapid onset of venom-induced pathology. In these experiments, IgG antivenom was more efficient than F(ab')(2) antivenom when administered after envenomation, probably as a consequence of differences in their pharmacokinetic profiles.

Revisiting saw-scaled viper (Echis carinatus) bites in the Jaffna Peninsula of Sri Lanka: distribution, epidemiology and clinical manifestations

In Sri Lanka, the saw-scaled viper (Echis carinatus) is distributed in the arid, dry and sandy coastal plains and in a prospective study we describe its bites in the Jaffna peninsula. Of the 304 snake bite admissions to the Jaffna Hospital in 2009, 217 (71.4%) were bitten by either venomous species or envenomed by unidentified snakes. There were 99 (45.6%) reported saw-scaled viper bites, of which 26 were confirmed cases. The length of the offending snakes ranged from 228-310mm and bites mainly occurred in the nearby islands. The median age of the confirmed cases was 34 years (range 1.5-72 years); occupations included housewives (8, 31%), school children (4, 15%) and farmers (2, 8%). In 18 patients (69%), bites occurred in daylight and in 8 (31%) within or near the compounds. The fingers were bitten in 8 (31%) and toes/foot in 11 (42%) cases. There were 2 (8%) dry bites and 19 patients (73%) developed local swelling; one patient developed haemorrhagic blisters. In 24 patients (92%), blood incoagulability manifested between 40 and 1095min after the bite, and three patients (12%) developed spontaneous bleeding. One patient (4%) developed mild acute renal dysfunction. The median time for correction of coagulopathy was 802min (range 180-1669min) with Indian polyvalent antivenom. All recovered. The saw scaled viper is responsible for most venomous bites in the Jaffna peninsula.

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.

Preclinical evaluation of caprylic acid-fractionated IgG antivenom for the treatment of Taipan (Oxyuranus scutellatus) envenoming in Papua New Guinea

BACKGROUND

Snake bite is a common medical emergency in Papua New Guinea (PNG). The taipan, Oxyuranus scutellatus, inflicts a large number of bites that, in the absence of antivenom therapy, result in high mortality. Parenteral administration of antivenoms manufactured in Australia is the current treatment of choice for these envenomings. However, the price of these products is high and has increased over the last 25 years; consequently the country can no longer afford all the antivenom it needs. This situation prompted an international collaborative project aimed at generating a new, low-cost antivenom against O. scutellatus for PNG.

METHODOLOGY/PRINCIPAL FINDINGS

A new monospecific equine whole IgG antivenom, obtained by caprylic acid fractionation of plasma, was prepared by immunising horses with the venom of O. scutellatus from PNG. This antivenom was compared with the currently used F(ab')(2) monospecific taipan antivenom manufactured by CSL Limited, Australia. The comparison included physicochemical properties and the preclinical assessment of the neutralisation of lethal neurotoxicity and the myotoxic, coagulant and phospholipase A(2) activities of the venom of O. scutellatus from PNG. The F(ab')(2) antivenom had a higher protein concentration than whole IgG antivenom. Both antivenoms effectively neutralised, and had similar potency, against the lethal neurotoxic effect (both by intraperitoneal and intravenous routes of injection), myotoxicity, and phospholipase A(2) activity of O. scutellatus venom. However, the whole IgG antivenom showed a higher potency than the F(ab')(2) antivenom in the neutralisation of the coagulant activity of O. scutellatus venom from PNG.

CONCLUSIONS/SIGNIFICANCE

The new whole IgG taipan antivenom described in this study compares favourably with the currently used F(ab')(2) antivenom, both in terms of physicochemical characteristics and neutralising potency. Therefore, it should be considered as a promising low-cost candidate for the treatment of envenomings by O. scutellatus in PNG, and is ready to be tested in clinical trials.

Pre-clinical assays predict pan-African Echis viper efficacy for a species-specific antivenom

Background

Snakebite is a significant cause of death and disability in subsistent farming populations of sub-Saharan Africa. Antivenom is the most effective treatment of envenoming and is manufactured from IgG of venom-immunised horses/sheep but, because of complex fiscal reasons, there is a paucity of antivenom in sub-Saharan Africa. To address the plight of thousands of snakebite victims in savannah Nigeria, the EchiTAb Study Group organised the production, testing and delivery of antivenoms designed to treat envenoming by the most medically-important snakes in the region. The Echis saw-scaled vipers have a wide African distribution and medical importance. In an effort to maximise the clinical utility of scarce antivenom resources in Africa, we aimed to ascertain, at the pre-clinical level, to what extent the E. ocellatus-specific EchiTAbG antivenom, which was designed specifically for Nigeria, neutralised the lethal activity of venom from two other African species, E. pyramidum leakeyi and E. coloratus.

Methodology/Principal Findings

Despite apparently quite distinctive venom protein profiles, we observed extensive cross-species similarity in the immuno-reactivity profiles of Echis species-specific antisera. Using WHO standard pre-clinical in vivo tests, we determined that the monospecific EchiTAbG antivenom was as effective at neutralising the venom-induced lethal effects of E. pyramidum leakeyi and E. coloratus as it was against E. ocellatus venom. Under the restricted conditions of this assay, the antivenom was ineffective against the lethal effects of venom from the non-African Echis species, E. carinatus sochureki.

Conclusions/Significance

Using WHO-recommended pre-clinical tests we have demonstrated that the new anti-E. ocellatus monospecific antivenom EchiTAbG, developed in response to the considerable snakebite-induced mortality and morbidity in Nigeria, neutralised the lethal effects of venoms from Echis species representing each taxonomic group of this genus in Africa. This suggests that this monospecific antivenom has potential to treat envenoming by most, perhaps all, African Echis species.

Snakebite is principally a health concern of rural poor communities. The high snakebite risk of subsistence farming and paucity of effective antivenoms in sub-Saharan Africa means that many communities remain unacceptably vulnerable to snakebite mortality and morbidity. There is therefore a compelling need to maximise the utility of the snakebite therapies that are available. To address Nigeria's severe snakebite problem, the government funded a collaboration of ministry officials, antivenom manufacturers and academics (the EchiTAb Study Group) to produce, test and deliver antivenom. Accordingly, we prepared EchiTAbG, an antivenom specific for envenoming by the saw-scaled viper (E. ocellatus) which is responsible for 80% of snakebite deaths in Nigeria. Since E. ocellatus is widely distributed across the West African savannah, EchiTAbG offers considerable therapeutic promise in many countries in the region. Since other Echis species represent public health concerns elsewhere in Africa, the objective of this study was to examine the pre-clinical intra-generic venom-neutralising efficacy of EchiTAbG. Our results suggest that EchiTAbG (Nigeria registration: A6-0078) has pan-African efficacy against Echis envenoming indicating that costly investment in region-specific antivenoms therefore may not be required. This represents an important progression to minimise development costs and maximise the delivery of snakebite therapy for the continent.