Bringing antivenoms to Sub-Saharan Africa

Comprehensive Review of Epidemiology and Treatment of Snakebite Envenomation in West Africa: Case of Benin

Snakebite envenomation (SBE) constitutes a public health, social, and economic problem affecting poor communities in intertropical and subtropical regions. This review sought to synthesize literature on snakebite envenomation in Benin to highlight research perspectives and strategies for better management of the menace. A literature search performed in multidisciplinary electronic databases showed that the prevalence of SBE is high in Benin, but the incidences, associated morbidities, and mortalities are greatly underestimated. Most snake envenomations are by Echis ocellatus in Northern Benin during the rainy season. Adults involved in agricultural activities are the most affected. The absence of antivenin serum in the most affected areas explains the preference for alternative and traditional medicine as the first-line treatment for SBE in Benin. In conclusion, it would be imperative to revitalize the snakebite reporting system in order to have better epidemiological data and to develop a sustainable national strategy for the control and management of snakebite envenomation.

Real life condition evaluation of Inoserp PAN-AFRICA antivenom effectiveness in Cameroon

BACKGROUND

Snakebites is a serious public health issue but remains a neglected tropical disease. Data on antivenom effectiveness are urgently needed in Africa. We assessed effectiveness of Inoserp PAN-AFRICA (IPA), the recommended antivenom available in Cameroon.

METHODOLOGY/PRINCIPAL FINDINGS

We enrolled 447 patients presenting with snakebite in 14 health facilities across Cameroon. At presentation, cytotoxicity, coagulation troubles and neurotoxicity were graded. We administered two to four vials of antivenom to patients based on hemotoxic or neurotoxic signs. We renewed antivenom administration to patients with persistence of bleedings or neurotoxicity 2 hours after each injection. We defined early improvement as a reduction of the grade of envenomation symptoms 2 hours after first injection. Medium-term effectiveness was investigated looking at disappearance of symptoms during hospitalization. After hospital discharge, a home visit was planned to assess long-term outcomes. Between October 2019 and May 2021, we enrolled 447 (93.7%), including 72% from the savannah regions. The median [IQR] age was 25 [14-40]. Envenomation was diagnosed in 369 (82.6%) participants. The antivenom was administered to 356 patients (96.5%) of whom 256 (71.9%) received one administration. Among these patients, cytotoxic symptoms were observed in 336 (94.4%) participants, coagulation disorders in 234 (65.7%) participants and neurotoxicity in 23 (6.5%) participants. Two hours after the first administration of antivenom, we observed a decrease in coagulation disorders or neurotoxicity in 75.2% and 39.1% of patients, respectively. Complete cessation of bleedings and neurotoxicity occurred in 96% and 93% of patients within 24 hours, respectively. Sequelae have been observed in 9 (3%) patients at the home visit 15 days after hospital admission and 11 (3%) died including one before antivenom injection.

CONCLUSIONS/SIGNIFICANCE

We confirmed good effectiveness of the IPA and highlighted the rapid improvement in bleeding or neurotoxicity after the first administration. Sequential administrations of low doses of antivenom, rigorously assessed at short intervals for an eventual renewal, can preserve patient safety and save antivenom.

TRIAL REGISTRATION

NCT03326492.

Comparing Traditional and Toxin-Oriented Approaches towards Antivenom Production against Bitis arietans Snake Venom

Accidents with snakes are responsible for about 32,000 deaths annually in sub-Saharan Africa, caused mostly by snakes from the genus Bitis, in particular Bitis arietans. B. arietans venom is composed of a complex mixture of toxins, mainly metalloproteases, serine proteases, phospholipases, lectins, and disintegrins. In this work, we compared two approaches to anti-B. arietans antivenom production: immunization with crude snake venom ("traditional approach") and immunization with selected key toxins isolated from the snake venom ("toxin oriented" approach). Fractions from B. arietans venom were isolated by size exclusion chromatography. Crude venom and samples containing serine proteases or metalloproteases were selected for the immunization of BALB/c mice. Anti-B. arietans and anti-serine proteases plasmas showed a similar recognition profile and higher titers and affinity than the anti-metalloproteases plasma. Cross-recognition of other Bitis venoms was observed, but with low intensity. Although the plasma of all experimental groups inhibited the enzymatic activity of B. arietans venom in vitro, in vivo protection was not achieved. Our results have shown limitations in both approaches considered. Based on this, we proposed a model of polyclonal, species-specific, monovalent antivenoms that could be used as a base to produce customizable polyvalent sera for use in sub-Saharan Africa.

Anti-Metalloproteases: Production and Characterization of Polyclonal IgG Anti-F2 Fraction Antibodies Purified from the Venom of the Snake Bitis arietans

Bitis arietans is a medically important snake found in Sub-Saharan Africa. The envenomation is characterized by local and systemic effects, and the lack of antivenoms aggravates the treatment. This study aimed to identify venom toxins and develop antitoxins. The F2 fraction obtained from Bitis arietans venom (BaV) demonstrated the presence of several proteins in its composition, including metalloproteases. Titration assays carried out together with the immunization of mice demonstrated the development of anti-F2 fraction antibodies by the animals. The determination of the affinity of antibodies against different Bitis venoms was evaluated, revealing that only BaV had peptides recognized by anti-F2 fraction antibodies. In vivo analyses demonstrated the hemorrhagic capacity of the venom and the effectiveness of the antibodies in inhibiting up to 80% of the hemorrhage and 0% of the lethality caused by BaV. Together, the data indicate: (1) the prevalence of proteins that influence hemostasis and envenomation; (2) the effectiveness of antibodies in inhibiting specific activities of BaV; and (3) isolation and characterization of toxins can become crucial steps in the development of new alternative treatments. Thus, the results obtained help in understanding the envenoming mechanism and may be useful for the study of new complementary therapies.

[Incidence of snakebites in rural communities living in the Paoua savannah and Mbaïki forest areas in Central African Republic]

Introduction

Snakebite is one of the most deadly neglected tropical diseases in Africa with more than 20,000 deaths reported each year. According to recent data from hospital in Central African Republic studies, the Paoua health district reports between 300 and 400 cases of ophidian envenomation each year. However, no epidemiological study on snakebites has been conducted at national level, nor a control strategy developed. The objective of this study is to describe the epidemiological aspects of snakebites in two rural communities, one located in savannah zone and the other in forest zone (both secondary and primary forest) in order to ensure adequate management of snakebites in these regions.

Method

Prospective community-based study in two health districts in the Central African Republic, the health district of Paoua in savannah area and the health district of Mbaïki in forest area, from December 2019 to January 2021. Snakebites were investigated in the community by selected trained people in charge of reporting data regarding all known cases of snakebites occurring during the study period. The data were actively notified either by health personal or community health workers in order to determine the circumstances and severity of the bite, its management and the clinical course in case of envenomation.

Results

A total of 412 snakebite cases were recorded during the study period, of which 198 cases occurred in the rural community of the forest zone and 214 in the community of the savannah zone. Case fatality rate was 5% in the forest zone and 1% in the savanna zone. The incidence rate of snakebite was significantly higher in savannah children compared to those in the forest (98/100,000 vs. 25.1/100,000; p<0.00001) while this incidence rate was significantly lower from age 45 onwards in the savannah area compared to the forest area (167/100,000 vs. 200/100,000; p=0.02). The case fatality rate of children and adults up to 44 years of age appeared to be significantly higher in the forest zone (7 deaths vs 1 death). Snakebites occurred significantly more frequently during field activities in the savannah zone than in the forest zone (51% vs 26%; p<0.0001). The symptomatology of bites was dominated by edema of the bitten limb and bleeding in the two study areas, compatible with cytotoxic and hemorrhagic syndromes due to viper bites.

Conclusion

With an incidence rate of more than 160 cases per 100,000 inhabitants in the active population aged 15-44 years in rural communities of the forest and savannah zone, snakebites remain a public health problem in Central African Republic. A study on the toxicity of snakebites in Central African Republic is recommended. Besides, it is urgent to make anti-venomous serums available in health facilities in order to reduce the mortality related to the envenomation.

Antibodies as Snakebite Antivenoms: Past and Future

Snakebite envenomation is considered a neglected tropical disease, affecting tens of thousands of people each year. The recommended treatment is the use of antivenom, which is composed of immunoglobulins or immunoglobulin fragments obtained from the plasma of animals hyperimmunized with one (monospecific) or several (polyspecific) venoms. In this review, the efforts made in the improvement of the already available antivenoms and the development of new antivenoms, focusing on snakes of medical importance from sub-Saharan Africa and Latin America, are described. Some antivenoms currently used are composed of whole IgGs, whereas others use F(ab’)2 fragments. The classic methods of attaining snake antivenoms are presented, in addition to new strategies to improve their effectiveness. Punctual changes in immunization protocols, in addition to the use of cross-reactivity between venoms from different snakes for the manufacture of more potent and widely used antivenoms, are presented. It is known that venoms are a complex mixture of components; however, advances in the field of antivenoms have shown that there are key toxins that, if effectively blocked, are capable of reversing the condition of in vivo envenomation. These studies provide an opportunity for the use of monoclonal antibodies in the development of new-generation antivenoms. Thus, monoclonal antibodies and their fragments are described as a possible alternative for the production of antivenoms, regardless of the venom. This review also highlights the challenges associated with their development.

Echis ocellatus Venom-Induced Reproductive Pathologies in Rat Model; Roles of Oxidative Stress and Pro-Inflammatory Cytokines

This study reported reproductive pathologies associated with Echis ocellatus venom in animal model. Twenty male Wistar rats with body weight between 180 and 220 g were selected randomly into two groups (n = 10). Rats in group 1 served as the control while rats in group 2 were envenomed with a single intraperitoneal injection of 0.055 mg/kg−1 (LD6.25) of E. ocellatus venom on the first day and a repeated dose on the twenty fifth day. Both control and envenomed rats were monitored for fifty consecutive days. The venom caused a significant (p < 0.05) reduction in sperm motility, count, and volume, with increased sperm anomalies in envenomed rats compared to the control. Likewise, serum concentrations of male reproductive hormones were significantly (p < 0.05) higher in envenomed rats. Increased levels of malondialdehyde were accompanied by a significant (p < 0.05) decrease in reduced glutathione and catalase activity in the epididymis and testis tissues of envenomed rats. The venom enhanced the release of epididymal and testicular tumor necrosis factor-alpha and interleukin1-beta compared to the control. Furthermore, severe pathological defects were noticed in tissues of the testis and epididymis of envenomed rats. This study demonstrated that E. ocellatus venom toxins can induce reproductive dysfunction in male victims of snake envenoming.

Prospects and Challenges of Developing Plant-Derived Snake Antivenin Natural Products: A Focus on West Africa

Snakebite envenomation (SBE) is an important public health issue that is now receiving renewed attention following its reclassification as a Neglected Tropical Disease (NTD). Most incidences occur in rural areas of resource-limited countries, as such, timely and appropriate medical care for SBE is often inaccessible. The administration of anti-snake venom serum (ASV) is the only effective definitive treatment of SBE, but treatment failure to available ASVs is not uncommon. Emerging evidence highlights the potential of small-molecule compounds as inhibitors against toxins of snake venom. This presents an encouraging prospect to develop an alternative therapeutic option for the treatment SBE, that may be amenable for use at the point of care in resource-constraint settings. In view of the pivotal role of natural products in modern drug discovery programmes, there is considerable interest in ethno-pharmacological mining of medicinal plants and plant-derived medicinal compounds toward developing novel snake venom-neutralising therapeutics. In this review, we compile a collection of medicinal plants used in the treatment of SBE in West Africa and highlight their promise as potential botanical drugs or as sources of novel small-molecule compounds for the treatment of SBE. The challenges that must be surmounted to bring this to fruition including the need for (sub) regional collaboration have been discussed.

Retrospective hospital-based study on snakebite envenomation in Sudan

BACKGROUND

Snakebite statistics are lacking in Sudan despite the high estimated burden. In this study we aimed to describe the incidence of snakebite envenomation and death in Sudan and to show the state-wise distribution of snakebite episode.

METHODS

We retrospectively analyzed hospital-based data on snakebite for 2014-2018. Data were obtained from the annual health statistical reports of the Ministry of Health. Descriptive statistics were used to illustrate the results.

RESULTS

A total of 63 160 people were envenomed during 2014-2018 with an average of 12 632 cases/year. The death rate between inpatient cases was 2.5%. The annual incidence was 18- 47 cases/100 000 population. Gadarif state recorded the highest incidence (132/100 000 population) of snakebite envenomation in Sudan whereas Northern state had the least incidence (5/100 000 population). The 15-24 y age group experienced the highest risk of snakebite and males were more exposed to snakebites than females.

CONCLUSIONS

Although hospital-based records underestimate the burden of snakebite, they can still provide an insight regarding the actual numbers. Here, we highlight the at-risk states in Sudan to be targeted for further questionnaire-based epidemiological studies and to guide health authorities to reduce the burden of snakebite envenomation by insuring proper antivenom distribution to the highly affected areas.

Delays, fears and training needs: Perspectives of health workers on clinical management of snakebite revealed by a qualitative study in Kitui County, Kenya

Key aims of the WHO Strategy to halve snakebite morbidity and mortality include health system strengthening and training of health workers. This requires knowledge of local health system needs and capacity, health worker training needs, and factors influencing health worker decision-making in snakebite management. This study explored health worker experiences and perceptions of snakebite management, both individually and in the context of their local health system.

We used a qualitative study design with semi-structured interviews (n = 14) and focus group discussions (n = 4). We employed a combination of sampling strategies aiming to achieve maximum variation among key informants within resource limitations. We recruited health workers (n = 33) of varying roles from purposively selected tier 2, 3 and 4 health facilities (n = 12) and the community (tier 1) in four sub-counties in Kitui County, Kenya. We conducted inductive thematic analysis of all transcripts.

The results identified that health workers recognised snake envenoming as a time-critical emergency in which delay in care seeking, sometimes exacerbated by health system referral delays, was a major barrier to effective management of patients. Clinicians strongly voiced a need for training in snakebite management, diagnosis and antivenom administration. Unexpressed needs for training were demonstrated in traditional remedy ineffectiveness, syndromic management, and critical appraisal of treatment effectiveness. Under-resourcing in antivenom, other medication, equipment, infrastructure and staffing also challenged management. Fear of snakebite and fear of antivenom, both linked to past experiences, influenced clinical decision-making.

Our findings clearly indicate a need in Kitui County for training programmes that equip health workers for clinical decision-making in snakebite management. We further identify community intervention needs to facilitate prompt presentation to healthcare, including practical affordable transport solutions, and systematic health system resourcing needs. In addition, we recommend supportive supervision and further research in response to the emotional stress resulting from managing difficult cases in under-resourced settings.

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Health workers managing snakebite patients expressed:•

Care-seeking and referral delays as major challenges to effective treatment.

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Anxiety managing severe cases and antivenom adverse reactions.

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Gaps in the availability of essential resources, from antivenom to electricity.

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Almost unanimous training needs in case management, diagnosis and antivenom use.

Integrating human behavior and snake ecology with agent-based models to predict snakebite in high risk landscapes

Snakebite causes more than 1.8 million envenoming cases annually and is a major cause of death in the tropics especially for poor farmers. While both social and ecological factors influence the chance encounter between snakes and people, the spatio-temporal processes underlying snakebites remain poorly explored. Previous research has focused on statistical correlates between snakebites and ecological, sociological, or environmental factors, but the human and snake behavioral patterns that drive the spatio-temporal process have not yet been integrated into a single model. Here we use a bottom-up simulation approach using agent-based modelling (ABM) parameterized with datasets from Sri Lanka, a snakebite hotspot, to characterise the mechanisms of snakebite and identify risk factors. Spatio-temporal dynamics of snakebite risks are examined through the model incorporating six snake species and three farmer types (rice, tea, and rubber). We find that snakebites are mainly climatically driven, but the risks also depend on farmer types due to working schedules as well as species present in landscapes. Snake species are differentiated by both distribution and by habitat preference, and farmers are differentiated by working patterns that are climatically driven, and the combination of these factors leads to unique encounter rates for different landcover types as well as locations. Validation using epidemiological studies demonstrated that our model can explain observed patterns, including temporal patterns of snakebite incidence, and relative contribution of bites by each snake species. Our predictions can be used to generate hypotheses and inform future studies and decision makers. Additionally, our model is transferable to other locations with high snakebite burden as well.

The WHO strategy for prevention and control of snakebite envenoming: a sub-Saharan Africa plan

Snakebite is a critical public health issue in tropical countries, particularly in Africa, where 20% of snakebites globally occur. In 2017, the WHO added snakebite envenoming to the category A of neglected tropical diseases. In 2019, thanks to broad institutional and international NGO support, including strong mobilization of African experts and governments, WHO launched a strategy for prevention and control of snakebite envenoming with more ambitious goals. In sub-Saharan Africa, accessibility of antivenoms and symptomatic, adjuvant or replacement therapy is a priority. Several antivenoms are available but their evaluation has not been properly carried out and they remain expensive. To date, there are no manufacturers of antivenom in sub-Saharan Africa (except in South Africa), which requires their importation from other continents. The lack of experience in antivenom choice and its use by health authorities, health personnel and population largely explains the shortage in sub-Saharan Africa. The deficiency of epidemiological data does not allow the implementation of appropriate and efficient care. It is crucial to strengthen the health system which does not have the necessary means for emergency management in general and envenoming in particular. Providing peripheral health centers with antivenoms would decrease complications and deaths. The motivation of communities at risk, identified through the epidemiological data, would be to reduce the delay in consultation that is detrimental to the efficiency of treatment. Partnerships need to be coordinated to optimize resources from international institutions, particularly African ones, and share the burden of treatment costs among all stakeholders. We propose here a project of progressive implementation of antivenom manufacturing in sub-Saharan Africa. The various steps, from the supply of appropriate venoms to the production of purified specific antibodies and vial filling, would be financed by international, regional and local funding promoting technology transfer from current manufacturers compensated by interest on the sale of antivenoms.

Ethnomedicinal plants used for snakebite treatments in Ethiopia: a comprehensive overview

Traditional medicine plays an important role in the daily lives of people living in rural parts of Ethiopia. Despite the fact that Ethiopia has a long history of using traditional medicinal plants as an alternative medicine source, there is no checklist compiling these plants used for snakebite treatment. This review collected and compiled available knowledge on and practical usage of such plants in the country. A literature review on medicinal plants used to treat snakebites was conducted from 67 journal articles, PhD dissertation and MSc theses available online. Data that summarize scientific and folk names, administration methods, plant portion used for treatment and method of preparation of recipes were organized and analyzed based on citation frequency. The summarized results revealed the presence of 184 plant species distributed among 67 families that were cited for treating snakebite in Ethiopia. In this literature search, no single study was entirely dedicated to the study of traditional medicinal plants used for the treatment of snakebite in Ethiopia. Most of the species listed as a snakebite remedy were shrubs and climbers (44%) followed by herbs (33%) and trees (23%). Fabaceae was the most predominant family with the greatest number of species, followed by Solanaceae and Vitaceae. Remedies are mainly prepared from roots and leaves, through decoctions, infusions, powders and juices. Most remedies were administered orally (69%). The six most frequently mentioned therapeutically important plants were Nicotiana tabacum, Solanum incanum, Carissa spinanrum, Calpurnia aurea, Croton macrostachyus and Cynodon dactylon. Authors reviewed the vegetal substances involved in snakebite management and their action mode. In addition to screening the biologically active ingredients and pharmacological activities of these plant materials, future studies are needed to emphasize the conservation and cultivation of important medicinal plants of the country.

A synthetic biology approach for consistent production of plant-made recombinant polyclonal antibodies against snake venom toxins

Antivenoms developed from the plasma of hyperimmunized animals are the only effective treatment available against snakebite envenomation but shortage of supply contributes to the high morbidity and mortality toll of this tropical disease. We describe a synthetic biology approach to affordable and cost-effective antivenom production based on plant-made recombinant polyclonal antibodies (termed pluribodies). The strategy takes advantage of virus superinfection exclusion to induce the formation of somatic expression mosaics in agroinfiltrated plants, which enables the expression of complex antibody repertoires in a highly reproducible manner. Pluribodies developed using toxin-binding genetic information captured from peripheral blood lymphocytes of hyperimmunized camels recapitulated the overall binding activity of the immune response. Furthermore, an improved plant-made antivenom (plantivenom) was formulated using an in vitro selected pluribody against Bothrops asper snake venom toxins and has been shown to neutralize a wide range of toxin activities and provide protection against lethal venom doses in mice.

Shortcomings in snake bite management in rural Cameroon: a case report

BACKGROUND

Snake bites are an important public health problem in developing countries with most bites occurring in rural areas. Severe envenomation often occurs in children and following bites to the face. Prompt administration of potent anti-venom remains the mainstay of management. However in Cameroon, the use of anti-venoms is limited by non-availability, high cost (where available) and poor mastery of treatment guidelines.

CASE PRESENTATION

We present a 10-year-old muslim Cameroonian child from an enclaved rural area, brought to the hospital 12 h after a snake bite to the face, with signs of severe envenomation. Despite the suboptimal anti-venom dose administered to this patient due to a stock out of this medication, supportive therapy was beneficial in ensuring a positive outcome and satisfactory recovery.

CONCLUSION

This highlights snake bites as a public health problem due to the lack of snake anti-venoms in peripheral health facilities, rendering them unable to appropriately manage these cases. National health policies should encourage constant peripheral availability of anti-venoms and the institution of an intervention package for snake bite management, comprising: treatment protocol, staff training, monitoring of compliance and community education to help reduce the mortality and morbidity from snake bites.

Preclinical Evaluation of the Efficacy of Antivenoms for Snakebite Envenoming: State-of-the-Art and Challenges Ahead

Animal-derived antivenoms constitute the mainstay in the therapy of snakebite envenoming. The efficacy of antivenoms to neutralize toxicity of medically-relevant snake venoms has to be demonstrated through meticulous preclinical testing before their introduction into the clinical setting. The gold standard in the preclinical assessment and quality control of antivenoms is the neutralization of venom-induced lethality. In addition, depending on the pathophysiological profile of snake venoms, the neutralization of other toxic activities has to be evaluated, such as hemorrhagic, myotoxic, edema-forming, dermonecrotic, in vitro coagulant, and defibrinogenating effects. There is a need to develop laboratory assays to evaluate neutralization of other relevant venom activities. The concept of the 3Rs (Replacement, Reduction, and Refinement) in Toxinology is of utmost importance, and some advances have been performed in their implementation. A significant leap forward in the study of the immunological reactivity of antivenoms against venoms has been the development of “antivenomics”, which brings the analytical power of mass spectrometry to the evaluation of antivenoms. International partnerships are required to assess the preclinical efficacy of antivenoms against snake venoms in different regions of the world in order to have a detailed knowledge on the neutralizing profile of these immunotherapeutics.

Successful post-exposure prophylaxis of Ebola infected non-human primates using Ebola glycoprotein-specific equine IgG

Herein we describe production of purified equine IgG obtained from horses immunized with plasmid DNA followed by boosting with Kunjin replicon virus-like particles both encoding a modified Ebola glycoprotein. Administration of the equine IgG over 5 days to cynomolgus macaques infected 24 hours previously with a lethal dose of Ebola virus suppressed viral loads by more than 5 logs and protected animals from mortality. Animals generated their own Ebola glycoprotein-specific IgG responses 9-15 days after infection, with circulating virus undetectable by day 15-17. Such equine IgG may find utility as a post-exposure prophylactic for Ebola infection and provides a low cost, scalable alternative to monoclonal antibodies, with extensive human safety data and WHO-standardized international manufacturing capability available in both high and low income countries.

Priority Actions and Progress to Substantially and Sustainably Reduce the Mortality, Morbidity and Socioeconomic Burden of Tropical Snakebite

The deliberations and conclusions of a Hinxton Retreat convened in September 2015, entitled “Mechanisms to reverse the public health neglect of snakebite victims” are reported. The participants recommended that the following priority actions be included in strategies to reduce the global impact of snake envenoming: (a) collection of accurate global snakebite incidence, mortality and morbidity data to underpin advocacy efforts and help design public health campaigns; (b) promotion of (i) public education prevention campaigns; (ii) transport systems to improve access to hospitals and (iii) establishment of regional antivenom-efficacy testing facilities to ensure antivenoms’ effectiveness and safety; (c) exploration of funding models for investment in the production of antivenoms to address deficiencies in some regions; (d) establishment of (i) programs for training in effective first aid, hospital management and post-treatment care of victims; (ii) a clinical network to generate treatment guidelines and (iii) a clinical trials system to improve the clinical management of snakebite; (e) development of (i) novel treatments of the systemic and local tissue-destructive effects of envenoming and (ii) affordable, simple, point-of-care snakebite diagnostic kits to improve the accuracy and rapidity of treatment; (f) devising and implementation of interventions to help the people and communities affected by physical and psychological sequelae of snakebite.

Retrospective study on the incidence of envenomation and accessibility to antivenom in Burkina Faso

Background

Snakebite is a common neglected public health issue, especially in poor rural areas of sub-Saharan Africa, Asia and Latin America. Passive immunotherapy with safe and effective antivenom is the only approved treatment for it. This study aimed to determine the incidence of snakebites, and to assess the availability and accessibility of antivenoms, from 2010 to 2014, in Burkina Faso.

Methods

The assessment of snakebite cases managed in all health facilities from 2010 to 2014 was performed from the Statistical Yearbook of the Ministry of Health. Antivenom consumption data were collected from the drug wholesalers established in Burkina Faso.

Results

Snakebites are among the five leading causes of consultations in health districts. From 2010 to 2014, 114,126 envenomation cases occurred in Burkina Faso, out of which 62,293 (54.6 %) victims have been hospitalized resulting in 1,362 (2 %) deaths. The annual incidence and mortality were respectively 130 bites and 1.75 deaths per 100,000 inhabitants. The amount of antivenom sold by wholesalers were 5,738 vials with a total cost of US$ 539,055 (annual average = US$ 107,811). The high cost of these antivenoms (between US$ 42 and 170 per dose according to brand) limited their use by rural people, the main victims of snakebites, whose income is insufficient. Thus, only 4 % of patients received antivenom treatment over the past five years. The price of antivenom was reduced in 2015 to US$ 3.4 by a public drug wholesaler.

Conclusion

The study confirmed the high burden of snakebites in Burkina Faso. To better manage envenomation, Burkina Faso implemented a strategy consisting in seeking affordable sources of antivenom supply of good quality and innovative mechanisms of subsidy.

Development of Equine IgG Antivenoms against Major Snake Groups in Mozambique

BACKGROUND

Snake envenoming is a significant public health problem in underdeveloped and developing countries. In sub-Saharan Africa, it is estimated that 90,000-400,000 envenomations occur each year, resulting in 3,500-32,000 deaths. Envenomings are caused by snakes from the Viperidae (Bitis spp. and Echis spp.) and Elapidae (Naja spp. and Dendroaspis spp.) families. The African continent has been suffering from a severe antivenom crisis and current antivenom production is only sufficient to treat 25% of snakebite cases. Our aim is to develop high-quality antivenoms against the main snake species found in Mozambique.

METHODS

Adult horses primed with the indicated venoms were divided into 5 groups (B. arietans; B. nasicornis + B. rhinoceros; N. melanoleuca; N. mossambica; N. annulifera + D. polylepis + D. angusticeps) and reimmunized two times for antivenom production. Blood was collected, and plasma was separated and subjected to antibody purification using caprylic acid. Plasmas and antivenoms were subject to titration, affinity determination, cross-recognition assays and in vivo venom lethality neutralization. A commercial anti-Crotalic antivenom was used for comparison.

RESULTS

The purified antivenoms exhibited high titers against B. arietans, B. nasicornis and B. rhinoceros (5.18 x 106, 3.60 x 106 and 3.50 x 106 U-E/mL, respectively) and N. melanoleuca, N. mossambica and N. annulifera (7.41 x 106, 3.07 x 106 and 2.60 x 106 U-E/mL, respectively), but lower titers against the D. angusticeps and D. polylepis (1.87 x 106 and 1.67 x 106 U-E/mL). All the groups, except anti-N. melanoleuca, showed significant differences from the anti-Crotalic antivenom (7.55 x 106 U-E/mL). The affinity index of all the groups was high, ranging from 31% to 45%. Cross-recognition assays showed the recognition of proteins with similar molecular weight in the venoms and may indicate the possibility of paraspecific neutralization. The three monospecific antivenoms were able to provide in vivo protection.

CONCLUSION

Our results indicate that the anti-Bitis and anti-Naja antivenoms developed would be useful for treating snakebite envenomations in Mozambique, although their effectiveness should to be increased. We propose instead the development of monospecific antivenoms, which would serve as the basis for two polyvalent antivenoms, the anti-Bitis and anti-Elapidae. Polyvalent antivenoms represent an increase in treatment quality, as they have a wider range of application and are easier to distribute and administer to snake envenoming victims.

Purification and characterization of five snake venom metalloproteinases from Egyptian Echis pyramidum pyramidum venom

New five P-III snake venom metalloproteinases (SVMPs): EpyB2 (62 kDa), EpyB3 (62+23 kDa), EpyB4 (60 kDa), EpyB5 (67 kDa) and EpyB6 (66 kDa) of the most dangerous viper, Echis pyramidum pyramidum (Epy), were purified and characterized in a set of biochemical assays. The SVMPs were purified by applying a protocol of two successive chromatographic steps. Three purified SVMPs "EpyB2, EpyB4, and EpyB5" have hemorrhagic activity with MHDs, 7 μg, 7.6 μg and 15 μg, respectively; furthermore, they have high preference towards fibronectin, collagen, gelatin, fibrin and hemoglobin substrates compared with non-hemorrhagic SVMPs (EpyB3 and EpyB6). All the purified SVMPs showed remarkable thermal and pH stability, inhibited by metalloproteinase inhibitors and Zn(2+), Mn(2+), Ni(2+), Co(2+), Cu(2+), and Hg(2+). The purified SVMPs act as α-fibrinogenases, prothrombin activators and procoagulants. In conclusion, Epy venom has multiple SVMPs that are responsible for hemorrhagic events and thus represent a significant health hazard for victims of envenomation, however, they may be useful for treating diseases involving abnormal blood clot formation.

African adders: partial characterization of snake venoms from three Bitis species of medical importance and their neutralization by experimental equine antivenoms

BACKGROUND

An alarming number of fatal accidents involving snakes are annually reported in Africa and most of the victims suffer from permanent local tissue damage and chronic disabilities. Envenomation by snakes belonging to the genus Bitis, Viperidae family, are common in Sub-Saharan Africa. The accidents are severe and the victims often have a poor prognosis due to the lack of effective specific therapies. In this study we have biochemically characterized venoms from three different species of Bitis, i.e., Bitis arietans, Bitis gabonica rhinoceros and Bitis nasicornis, involved in the majority of the human accidents in Africa, and analyzed the in vitro neutralizing ability of two experimental antivenoms.

METHODOLOGY/PRINCIPAL FINDINGS

The data indicate that all venoms presented phospholipase, hyaluronidase and fibrinogenolytic activities and cleaved efficiently the FRET substrate Abz-RPPGFSPFRQ-EDDnp and angiotensin I, generating angiotensin 1-7. Gelatinolytic activity was only observed in the venoms of B. arietans and B. nasicornis. The treatment of the venoms with protease inhibitors indicated that Bitis venoms possess metallo and serinoproteases enzymes, which may be involved in the different biological activities here evaluated. Experimental antivenoms produced against B. arietans venom or Bitis g. rhinoceros plus B. nasicornis venoms cross-reacted with the venoms from the three species and blocked, in different degrees, all the enzymatic activities in which they were tested.

CONCLUSION

These results suggest that the venoms of the three Bitis species, involved in accidents with humans in the Sub-Saharan Africa, contain a mixture of various enzymes that may act in the generation and development of some of the clinical manifestations of the envenomations. We also demonstrated that horse antivenoms produced against B. arietans or B. g. rhinoceros plus B. nasicornis venoms can blocked some of the toxic activities of these venoms.

Engineering venom's toxin-neutralizing antibody fragments and its therapeutic potential

Serum therapy remains the only specific treatment against envenoming, but anti-venoms are still prepared by fragmentation of polyclonal antibodies isolated from hyper-immunized horse serum. Most of these anti-venoms are considered to be efficient, but their production is tedious, and their use may be associated with adverse effects. Recombinant antibodies and smaller functional units are now emerging as credible alternatives and constitute a source of still unexploited biomolecules capable of neutralizing venoms. This review will be a walk through the technologies that have recently been applied leading to novel antibody formats with better properties in terms of homogeneity, specific activity and possible safety.

The use of ecological niche modeling to infer potential risk areas of snakebite in the Mexican state of Veracruz

Background

Many authors have claimed that snakebite risk is associated with human population density, human activities, and snake behavior. Here we analyzed whether environmental suitability of vipers can be used as an indicator of snakebite risk. We tested several hypotheses to explain snakebite incidence, through the construction of models incorporating both environmental suitability and socioeconomic variables in Veracruz, Mexico.

Methodology/Principal Findings

Ecological niche modeling (ENM) was used to estimate potential geographic and ecological distributions of nine viper species' in Veracruz. We calculated the distance to the species' niche centroid (DNC); this distance may be associated with a prediction of abundance. We found significant inverse relationships between snakebites and DNCs of common vipers (Crotalus simus and Bothrops asper), explaining respectively 15% and almost 35% of variation in snakebite incidence. Additionally, DNCs for these two vipers, in combination with marginalization of human populations, accounted for 76% of variation in incidence.

Conclusions/Significance

Our results suggest that niche modeling and niche-centroid distance approaches can be used to mapping distributions of environmental suitability for venomous snakes; combining this ecological information with socioeconomic factors may help with inferring potential risk areas for snakebites, since hospital data are often biased (especially when incidences are low).

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.

Use of antivenoms for the treatment of envenomation by Elapidae snakes in Guinea, Sub-Saharan Africa

Background

In Guinea Elapids are responsible for 20% of envenomations. The associated case fatality rate (CFR) ranged 15-27%, irrespective of treatment.

Results

We studied 77 neurotoxic envenomations divided in 3 groups: a set of patients that received only traditional or symptomatic treatments, and two other groups that received either 2 or 4 initial vials of Antivipmyn® Africa renewed as necessary. CFR was 27.3%, 15.4% and 17.6%, respectively. Although antivenom treatment was likely to reduce CFR, it didn’t seem to have an obvious clinical benefit for the patients, suggesting a low treatment efficacy. Mean delay to treatment or clinical stages were not significantly different between the patients who recovered and the patients who died, or between groups. Interpretation of these results is complicated by the lack of systematic studies under comparable conditions. Of particular importance is the absence of assisted ventilation, available to patients in all the other clinical studies of neurotoxic envenomation.

Conclusion

The apparent lack of clinical benefit may have several causes. The hypothesis of a limited therapeutic window, i.e. an insufficient formation of antigen-antibody complexes once toxins are bound to their targets and/or distributed beyond the reach of antivenom, should be explored.

Correlation between annual activity patterns of venomous snakes and rural people in the Niger Delta, southern Nigeria

BACKGROUND

Venomous snakes are among the most serious health hazards for rural people in tropical regions of the world. Herein we compare the monthly activity patterns of eight venomous snake species (Elapidae and Viperidae) with those of rural people in the Niger Delta area of southern Nigeria, in order to identify the periods of highest potential risk for persons, and the human group actually at greater risk of snakebite.

RESULTS

We documented that above-ground activity of all venomous snakes peaked in the wet season, and that high snake activity and high human activity were most highly correlated between April and August. In addition, we documented that women and teenagers were at relatively higher risk of encountering a venomous snake than adult males, despite they are less often in the field than men.

CONCLUSIONS

Our results suggest that future programs devoted to mitigate the social and health effects of snakebites in the Niger Delta region should involve especially women and teenagers, with ad-hoc education projects if appropriate. We urge that international organizations working on social and health problems in the developing world, such as IRD, DFID, UNDP, should provide advice through specific programs targeted at especially these categories which have been highlighted in comparatively potential higher threat from snakebites than adult men.

Morbidity and mortality following envenomation by the common night adder (Causus rhombeatus) in three dogs

In South Africa dogs are frequently presented to veterinarians following snakebite. The offending snakes are usually puff adders (Bitis arietans), cobras (Naja spp.) and mambas (Dendroaspis spp.). Night adder (Causus rhombeatus) bites in dogs have not yet been reported in South Africa. This article deals with three cases of dogs bitten by night adders in which extensive tissue damage was noted and one fatality occurred. Night adder bites may be indistinguishable from puff adder bites. Non-specific treatment included addressing the hypovolaemia and swelling. Specific treatment involving immunotherapy using the South African polyvalent antivenom would be ineffective as it does not contain immunoglobulins against night adder venom. Veterinarians should also include night adders as the possible cause of dogs suffering from severe and painful swellings suspected to be due to snakebites.

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.

Identification of linear B-cell epitopes on myotoxin II, a Lys49 phospholipase A₂ homologue from Bothrops asper snake venom

Knowledge on toxin immunogenicity at the molecular level can provide valuable information for the improvement of antivenoms, as well as for understanding toxin structure-function relationships. The aims of this study are two-fold: first, to identify the linear B-cell epitopes of myotoxin II from Bothrops asper snake venom, a Lys49 phospholipase A₂ homologue; and second, to use antibodies specifically directed against an epitope having functional relevance in its toxicity, to probe the dimeric assembly mode of this protein in solution. Linear B-cell epitopes were identified using a library of overlapping synthetic peptides spanning its complete sequence. Epitopes recognized by a rabbit antiserum to purified myotoxin II, and by three batches of a polyvalent (Crotalidae) therapeutic antivenom (prepared in horses immunized with a mixture of B. asper, Crotalus simus, and Lachesis stenophrys venoms) were mapped using an enzyme-immunoassay based on the capture of biotinylated peptides by immobilized streptavidin. Some of the epitopes identified were shared between the two species, whereas others were unique. Differences in epitope recognition were observed not only between the two species, but also within the three batches of equine antivenom. Epitope V, located at the C-terminal region of this protein, is known to be relevant for toxicity and neutralization. Affinity-purified rabbit antibodies specific for this site were able to immunoprecipitate myotoxin II, suggesting that the two copies of epitope V are simultaneously available to antibody binding, which would be compatible with the mode of dimerization known as "conventional" dimer.

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.

[Clinical study of tolerance and effectiveness of a F(ab')(2) polyvalent antienom for African snake bites in Kindia, Guinea]

An open, pragmatic, phase IV clinical trial was undertaken to measure tolerance and assess the effectiveness of Antivipmyn® Africa, antivenom composed of lyophilized F(ab')(2) fragments of immunoglobulin G in field conditions. The study was conducted at the Institut Pasteur of Guinea (IPG) from August 2009 to February 2010. Two hundred twenty-eight victims of snakebites presented at the processing center of the IPG during this period, including one hundred fifty (65.8%) envenomations, mostly young men. One hundred twenty-four of them (82.7%) suffered from viper envenomations and 26 (17.3%) from elapid ones. All patients were treated by intravenous Antivipmyn® Africa, averaging 1.4 (± 1.0) vials, more in patients with neurotoxic envenomation than others (P < 10(-5)). Four patients (2.7%), showing cobralike envenomation, died shortly after their arrival at the IPG despite the administration of the antivenom. Ten patients showed mild side effects (rash or pruritus), out of which 5 (3.3%) were probably due to treatment. This study confirms the efficacy and safety of Antivipmyn® Africa.

Proteomic and biological characterization of the venom of the redtail coral snake, Micrurus mipartitus (Elapidae), from Colombia and Costa Rica

Venoms of the redtail coral snake Micrurus mipartitus from Colombia and Costa Rica were analyzed by "venomics", a proteomic strategy to determine their composition. Proteins were separated by RP-HPLC, followed by SDS-PAGE, in-gel tryptic digestion, identification by MALDI or ESI tandem mass spectrometry, and assignment to known protein families by similarity. These analyses were complemented with a characterization of venom activities in vitro and in vivo. Proteins belonging to seven families were found in Colombian M. mipartitus venom, including abundant three-finger toxins (3FTx; ~60% of total proteins) and phospholipases A(2) (PLA(2); ~30%), with the remaining ~10% distributed among l-amino acid oxidase, P-III metalloproteinase, Kunitz-type inhibitor, serine proteinase, and C-type lectin-like families. The venoms of two M. mipartitus specimens from Costa Rica, also referred to as M. multifasciatus in some taxonomic classifications, were also analyzed. Both samples were highly similar to each other, and partially resembled the chromatographic and identity profiles of M. mipartitus from Colombia, although presenting a markedly higher proportion of 3FTxs (~83.0%) in relation to PLA(2)s (~8.2%), and a small amount of acetylcholinesterase, not detected in the venom from Colombia. An equine antivenom against the Central American coral snake, M. nigrocinctus, did not recognize venom components of M. mipartitus from Colombia or Costa Rica by enzyme-immunoassay. Four major components of Colombian M. mipartitus venom were isolated and partially characterized. Venomics of Micrurus species may provide a valuable platform for the rational design of immunizing cocktails to obtain polyspecific antivenoms for this highly diverse group of American elapids.

Venomic analysis and evaluation of antivenom cross-reactivity of South American Micrurus species

Coral snakes from Micrurus genus are the main representatives of the Elapidae family in South America. However, biochemical and pharmacological features regarding their venom constituents remain poorly investigated. Here, venomic analyses were carried out aiming at a deeper understanding on the composition of M. frontalis, M. ibiboboca, and M. lemniscatus venoms. In the three venoms investigated, proteins ranging from 6 to 8 kDa (3FTx) and 12 to 14 kDa (PLA(2)) were found to be the most abundant. Also, the N-terminal sequences of four new proteins, purified from the M. lemniscatus venom, similar to 3FTx, PLA(2) and Kunitz-type protease inhibitor from other Micrurus and elapid venoms are reported. Cross-reactivity among different Micrurus venoms and homologous or heterologous antivenoms was carried out by means of 2D-electrophoresis and immunoblotting. As, expected, the heterologous anti-Elapid venom displayed the highest degree of cross-reactivity. Conversely, anti-M. corallinus reacted weakly against the tested venoms. In gel digestions, followed by mass spectrometry sequencing and similarity searching, revealed the most immunogenic protein families as similar to short and long neurotoxins, weak neurotoxins, PLA(2), β-bungarotoxin, venom protein E2, frontoxin III, LAO and C-type lectin. The implications of our results for the production of Micrurus antivenoms are discussed.

Research strategies to improve snakebite treatment: challenges and progress

Antivenom is an effective treatment of snakebite but, because of the complex interplay of fiscal, epidemiological, therapeutic efficacy and safety issues, the mortality of snakebite remains unacceptably high. Efficiently combating this high level of preventable death amongst the world's most disadvantaged communities requires the globally-coordinated action of multiple intervention programmes. This is the overall objective of the Global Snakebite Initiative. This paper describes the challenges facing the research community to develop snakebite treatments that are more efficacious, safe and affordable than current therapy.

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.

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.

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

BACKGROUND

In West Africa, envenoming by saw-scaled or carpet vipers (Echis ocellatus) causes great morbidity and mortality, but there is a crisis in supply of effective and affordable antivenom (ISRCTN01257358).

METHODS

In a randomised, double-blind, controlled, non-inferiority trial, "EchiTAb Plus-ICP" (ET-Plus) equine antivenom made by Instituto Clodomiro Picado was compared to "EchiTAb G" (ET-G) ovine antivenom made by MicroPharm, which is the standard of care in Nigeria and was developed from the original EchiTAb-Fab introduced in 1998. Both are caprylic acid purified whole IgG antivenoms. ET-G is monospecific for Echis ocellatus antivenom (initial dose 1 vial) and ET-Plus is polyspecific for E. ocellatus, Naja nigricollis and Bitis arietans (initial dose 3 vials). Both had been screened by pre-clinical and preliminary clinical dose-finding and safety studies. Patients who presented with incoagulable blood, indicative of systemic envenoming by E. ocellatus, were recruited in Kaltungo, north-eastern Nigeria. Those eligible and consenting were randomly allocated with equal probability to receive ET-Plus or ET-G. The primary outcome was permanent restoration of blood coagulability 6 hours after the start of treatment, assessed by a simple whole blood clotting test repeated 6, 12, 18, 24 and 48 hr after treatment. Secondary (safety) outcomes were the incidences of anaphylactic, pyrogenic and late serum sickness-type antivenom reactions.

FINDINGS

Initial doses permanently restored blood coagulability at 6 hours in 161/194 (83.0%) of ET-Plus and 156/206 (75.7%) of ET-G treated patients (Relative Risk [RR] 1.10 one-sided 95% CI lower limit 1.01; P = 0.05). ET-Plus caused early reactions on more occasions than did ET-G [50/194 (25.8%) and 39/206 (18.9%) respectively RR (1.36 one-sided 95% CI 1.86 upper limit; P = 0.06). These reactions were classified as severe in 21 (10.8%) and 11 (5.3%) of patients, respectively.

CONCLUSION

At these doses, ET-Plus was slightly more effective but ET-G was slightly safer. Both are recommended for treating E. ocellatus envenoming in Nigeria.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN01257358.

Antivenomic assessment of the immunological reactivity of EchiTAb-Plus-ICP, an antivenom for the treatment of snakebite envenoming in sub-Saharan Africa

The immunoreactivity of EchiTAb-Plus-ICP, an antivenom developed for the treatment of snakebite envenoming in sub-Saharan Africa, to venoms of seven Echis and Bitis species, was assessed by "antivenomics." This proteomic approach is based on the ability of an antivenom to immunodeplete homologous or heterologous venom proteins. Our results show an extensive cross-reactivity of this antivenom against all Echis and Bitis venoms studied, as revealed by the complete immunodepletion of the majority of venom components, including metalloproteinases, serine proteinases, C-type lectin-like proteins, some phospholipases A(2) and L-amino acid oxidase. However, some phospholipases A(2), disintegrins and proteinase inhibitors were immunodepleted to only a partial extent. These results support the hypothesis that immunizing horses with a mixture of the venoms of Echis ocellatus, Bitis arietans, and Naja nigricollis generates antibodies capable of recognizing the majority of components of medically-relevant homologous and heterologous viperid venoms of the genera Bitis and Echis from sub-Saharan Africa.