First clinical experiences with a new ovine Fab Echis ocellatus snake bite antivenom in Nigeria: randomized comparative trial with Institute Pasteur Serum (Ipser) Africa antivenom

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.

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.

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.

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.

Amputation and disability following snakebite in Nigeria

Snakebite is an important cause of amputation and disability in rural communities throughout the tropics. However, the details of the causes, types and estimates of disability are lacking. This report describes 16 snakebite victims who had amputations, including two who had above-knee amputations. The patients presented with limb swelling (16), gangrene (15), ischaemia (4) and three had possible compartment syndrome. All the patients used ineffective time wasting remedies that were potentially harmful as first-aid. The median delay to hospital following bite was 2.5 days. In order to prevent disability, efforts should be made to: reduce delay before hospital presentation; improve the knowledge of first-aid; provide effective antivenoms; improve wound and clinical care in communities; and improve facilities.

Development of a sensitive enzyme immunoassay for measuring taipan venom in serum

The detection and measurement of snake venom in blood is important for confirming snake identification, determining when sufficient antivenom has been given, detecting recurrence of envenoming, and in forensic investigation. Venom enzyme immunoassays (EIA) have had persistent problems with poor sensitivity and high background absorbance leading to false positive results. This is particularly problematic with Australasian snakes where small amounts of highly potent venom are injected, resulting in low concentrations being associated with severe clinical effects. We aimed to develop a venom EIA with a limit of detection (LoD) sufficient to accurately distinguish mild envenoming from background absorbance at picogram concentrations of venom in blood. Serum samples were obtained from patients with taipan bites (Oxyuranus spp.) before and after antivenom, and from rats given known venom doses. A sandwich EIA was developed using biotinylated rabbit anti-snake venom antibodies for detection. For low venom concentrations (i.e. <1 ng/mL) the assay was done before and after addition of antivenom to the sample (antivenom difference method). The LoD was 0.15 ng/mL for the standard assay and 0.1 ng/mL for the antivenom difference method. In 11 pre-antivenom samples the median venom concentration was 10 ng/mL (Range: 0.3-3212 ng/mL). In four patients with incomplete venom-induced consumption coagulopathy the median venom concentration was 2.4 ng/mL compared to 30 ng/mL in seven patients with complete venom-induced consumption coagulopathy. No venom was detected in any post-antivenom sample and the median antivenom dose prior to this first post-antivenom sample was 1.5 vials (1-3 vials), including 7 patients administered only 1 vial. In rats the assay distinguished a 3-fold difference in venom dose administered and there was small inter-individual variability. There was small but measurable cross-reactivity with black snake (Pseudechis), tiger snake (Notechis) and rough-scale snake (Tropidechis carinatus) venoms with the assay for low venom concentrations (<1 ng/mL). The use of biotinylation and the antivenom difference method in venom EIA produces a highly sensitive assay that will be useful for determining antivenom dose, forensic and clinical diagnosis.

Snake bite

Snake bite is a common and frequently devastating environmental and occupational disease, especially in rural areas of tropical developing countries. Its public health importance has been largely ignored by medical science. Snake venoms are rich in protein and peptide toxins that have specificity for a wide range of tissue receptors, making them clinically challenging and scientifically fascinating, especially for drug design. Although the full burden of human suffering attributable to snake bite remains obscure, hundreds of thousands of people are known to be envenomed and tens of thousands are killed or maimed by snakes every year. Preventive efforts should be aimed towards education of affected communities to use proper footwear and to reduce the risk of contact with snakes to a minimum through understanding of snakes' behaviour. To treat envenoming, the production and clinical use of antivenom must be improved. Increased collaboration between clinicians, epidemiologists, and laboratory toxinologists should enhance the understanding and treatment of envenoming.

Snakebite envenoming from a global perspective: Towards an integrated approach

Snakebite envenoming is a neglected public health challenge of compelling importance in many regions of the world, particularly sub-Saharan Africa, Asia, Latin America and Papua-New Guinea. Addressing the problem of snakebite effectively demands an integrated multifocal approach, targeting complex problems and involving many participants. It must comprise: (a) Acquisition of reliable information on the incidence and mortality attributable to snakebite envenoming, and the number of people left with permanent sequelae. (b) Improvements in production of effective and safe antivenoms, through strategies aimed at strengthening the technological capacity of antivenom manufacturing laboratories. (c) Increasing the capacity of low-income countries to produce specific immunogens(snake venoms) locally, and to perform their own quality control of antivenoms. (d) Commitments from regional producers to manufacture antivenoms for countries where antivenom production is not currently feasible. (e) Implementation of financial initiatives guaranteeing the acquisition of adequate volumes of antivenom at affordable prices in low-income countries. (f) Performance of collaborative studies on the safety and effectiveness of antivenoms assessed preclinically and by properly designed clinical trials. (g) Development of antivenom distribution programmes tailored to the real needs and epidemiological situations of rural areas in each country. (h) Permanent training programmes for health staff, particularly in rural areas where snakebites are frequent.(i) Implementation of programmes to support those people whose snakebites resulted in chronic disabilities. (j) Preventive and educational programmes at the community level, with the active involvement of local organizations and employing modern methods of health promotion. Such an integrated approach, currently being fostered by the Global Snake Bite Initiative of the International Society on Toxinology and by the World Health Organization, will help to alleviate the enormous burden of human suffering inflicted by snakebite envenoming.

Envenoming after carpet viper (Echis ocellatus) bite during pregnancy: timely use of effective antivenom improves maternal and foetal outcomes

The report describes successful management of 10 women in 2nd and 3rd pregnancy trimesters with EchiTab IgG antivenom after carpet viper (Echis ocellatus) envenoming. All women survived but foetal loss in a victim with delayed presentation and a case of mild hypersensitivity reaction were recorded. Excellent outcomes can be achieved in rural and semi-nomadic populations without specialized care and immediate access and provision of effective antivenoms is paramount in curtailing snakebite maternal morbidity, mortality and foetal loss.

Failure of a new antivenom to treat Echis ocellatus snake bite in rural Ghana: the importance of quality surveillance

This study compares two antivenoms used to treat Echis ocellatus snake bite patients at Mathias Hospital, Yeji, central Ghana. FAV-Afrique antivenom (Aventis Pasteur) was given to 278 patients during 2001--2003, whilst Asna Antivenom C (Bharat Serum and Vaccines Ltd) was used in 2004 to treat 66 patients. The two groups had comparable patient attributes, time from snake bite to treatment and staff adherence to the tested treatment protocol. The antivenom C group required more repeat doses and twice the amount of antivenom to treat coagulopathy. Of greater concern, the antivenom C mortality rate was 12.1%, a marked rise from the 1.8% rate in the earlier FAV-Afrique antivenom group. In this study, antivenom C was ineffective as treatment for West African E. ocellatus snake venom. This illustrates the absolute need for regional pilot tests to assess the effectiveness of a new antivenom against local snake venoms before its sole and general distribution in a region is initiated.

Treatment of snakebite in Australia: the current evidence base and questions requiring collaborative multicentre prospective studies

Despite the wealth of anecdotes and case reports there are fundamental questions of management of snakebite in Australia that remain unresolved or for which the current evidence is limited. The efficacy in the field, potential limitations and possibility of improvements in pressure immobilisation first aid need objective studies in humans. Optimal bandage sizes, stretch and pressure for different sized limbs need further evaluation, as does the use of pressure pads. Better definitions of specific clinical envenoming syndromes attributable to individual snake species are required, including elucidation of within-genus variations, similarities and differences. Venom studies suggest this is especially important for species within the brown snake (Pseudonaja) and death adder (Acanthophis) genera. Appropriate antivenom types, doses and dosing intervals for individual snake species should be more formally studied in patients. Especially important are confirmation of the need for higher doses of brown snake antivenom, while possibly limiting unnecessarily high doses, confirmation of the critical importance of early antivenom use to prevent pre-synaptic neurotoxicity in Taipan and tiger snake bites and ascertainment of whether larger doses of antivenom are unhelpful in Taipan bites after specified time delays. Confirmation of clinical efficacy and dosing recommendations for use of tiger snake (Notechis) antivenom in envenoming from Australian copperhead (Austrelaps spp.), broad headed (Hoplocephalus spp.) and rough-scaled snakes (Tropidechis carinatus) also require formal study in patients. Other examples of clinical relevance of cross-specificity of current and future monospecific antivenoms and whether there are geographical variations in antivenom responses within species will require elucidation. Prospective multicentre collaborative studies with predefined data collection and serial venom level assays are proposed as the way forward in Australia to help resolve therapeutic uncertainties and to establish a firmer evidence base for best-practice treatment guidelines for Australasian elapid snakebite.

Enzyme immunoassays in brown snake (Pseudonaja spp.) envenoming: Detecting venom, antivenom and venom–antivenom complexes

Although a commercial snake venom detection kit (SVDK) is available to distinguish between the five major snake groups in Australia, there is no assay for quantifying venom or antivenom concentrations in envenomed patients. Serum samples were obtained from patients with brown snake (Pseudonaja spp.) envenoming before and after the administration of antivenom and patients with suspected brown snake bites but no evidence of envenoming. Enzyme immunoassays (EIAs) were developed for free venom, free antivenom and the venom-antivenom complex. Standard samples measured in duplicate had a coefficient of variation of less than 10%. The EIA for venom was able to detect brown snake venom down to concentrations of 3 ng/mL. A high baseline absorbance was measured in some patients that did not change with the addition of excess antivenom to the samples. In these patients, the baseline absorbance was subtracted from all measurements to calculate the true venom concentration. The EIA for brown snake antivenom had a limit of detection of 20 microg/mL, but 50 microg/mL was used as a cut-off based on assays in patients who had not received antivenom. The EIA for venom-antivenom complexes was unable to detect these at the low venom concentrations that occurred in patients. Quantification of venom and antivenom will help to determine the dose of antivenom required to bind venom and to establish appropriate end points for antivenom treatment.

Snakebite in northern Cameroon: 134 victims of bites by the saw-scaled or carpet viper, Echis ocellatus

Echis ocellatus is one of the most deadly snakes known to humans, yet the procurement of antivenom for the treatment of these snakebites in Africa has become increasingly difficult and expensive. There is no consensus for the management of victims, and little is known of actual recent experiences with these cases in ordinary health care settings in Africa. All cases of snakebite reliably identified as bites of E. ocellatus and admitted to Kolofata District Hospital, northern Cameroon, from January 1993 to December 2002 were described retrospectively or prospectively. Of 134 cases admitted, 63% were male, three-quarters were aged < 30 years, and 85% survived. Pasteur polyvalent antivenom for Africa was administered intravenously in all but 1 case, but patients rarely received more than 10 mL. In most cases, appropriate antivenom can be administered effectively at a fraction of the recommended dose (20-60 mL), even in patients with serious complications presenting days after having been bitten; however, death is more likely in late presenters.

Pharmacokinetics of a F(ab')2 scorpion antivenom in healthy human volunteers

This paper presents the first study of F(ab')2 scorpion antivenom pharmacokinetics in humans. We have studied the pharmacokinetics of an antiscorpion venom preparation (Alacramyn) in eight human healthy volunteers. The fabotherapic was administered as a 47.5 mg i.v. bolus. Blood samples were drawn at 0, 5, 15, 30, 45, 60, 90, 120, 180 and 360 min after antivenom administration. Subsequently, the volunteers made seven visits to the hospital. Four of them at 24 h intervals, one at day 10, and one at day 21. We measured antivenom plasmatic concentrations using a specific high sensitivity ELISA method for F(ab')2. The time course of F(ab')2 in serum of seven subjects was well described by a lineal combination of three exponential components; a four exponential component model was necessary to fit the eighth subject. The most significant antivenom pharmacokinetic parameters determined were: AUC(infinity)=596.9 (369.3, 891.2) mg h l(-1); V(c) = 3.1 (2.3, 4.3)l; V(ss) = 15.4 (12.8, 39.9)l; MRT = 250.0 (218.8, 310.2) h; CL = 96.6 (58.0, 139.2) ml h(-1); t(1/2,tau1) (also called t(1/2,alpha)) = 0.25 (0.13, 0.37) h; t(1/2,tau(z)) (corresponding to the slowest component) = 161.3 (141.0, 212.0) h.

Antigenic relationships and relative immunogenicities of isolated metalloproteinases from Echis ocellatus venom

The antigenic relationship between snake venom metalloproteinases (SVMPs) was analysed using rabbit antisera raised against the native forms of two SVMPs purified from Echis ocellatus venom. Using enzyme-linked immunosorbent assay (ELISA), western blotting and two-dimensional SDS-PAGE, our findings show that antibodies raised against EoVMP1, a non-haemorrhagic class P-I 24kDa SVMP, and EoVMP2, a haemorrhagic class P-III 56kDa SVMP, demonstrate cross-reactivities which relate to the domain hierarchy observed in class P-I to P-III/IV SVMPs. A third 65kDa P-III metalloproteinase (designated EoVMP3) was also isolated from E. ocellatus venom using hydrophobic interaction, size exclusion and anion exchange chromatography. In comparative immunoassays, EoVMP2 and EoVMP3 bound strongly to the commercial monovalent ovine Fab fragment antivenom EchiTAbtrade mark (raised against the same venom), but EoVMP1 showed no cross-reactivity. This could indicate that antivenoms may lack antibodies to potentially important venom components.

Production and purification of ovine anti-tetanus antibody

We used the ovine as bioreactor for the production and optimization of anti-tetanus toxin antibody. Four female sheep were immunized with human tetanus vaccine (TT-alum) every two weeks for 16 weeks, after which serum was collected and its titer was estimated by ELISA. The highest titer obtained was 39,000 IU ml-1. To optimize a purification protocol for ovine anti-tetanus toxin, we used four procedures; weak anion (DEAE-Sephadex), weak cation (CM-Sephadex), ammonium sulfate precipitation alone or in combination with caprylic acid. Fifty percent saturation with ammonium sulfate combined with caprylic acid gave us the highest yield of protein with specific activity and the purest Fab product.

Assessment of the viral safety of antivenoms fractionated from equine plasma

Antivenoms are preparations of intact or fragmented (F(ab′)₂ or Fab) immunoglobulin G (IgG) used in human medicine to treat the severe envenomings resulting from the bites and stings of various animals, such as snakes, spiders, scorpions, or marine animals, or from the contact with poisonous plants. They are obtained by fractionating plasma collected from immunized horses or, less frequently, sheep. Manufacturing processes usually include pepsin digestion at acid pH, papain digestion, ammonium sulphate precipitation, caprylic acid precipitation, heat coagulation and/or chromatography. Most production processes do not have deliberately introduced viral inactivation or removal treatments, but antivenoms have never been found to transmit viruses to humans. Nevertheless, the recent examples of zoonotic diseases highlight the need to perform a careful assessment of the viral safety of antivenoms.

This paper reviews the characteristics of equine viruses of antivenoms and discusses the potential of some manufacturing steps to avoid risks of viral contamination. Analysis of production parameters indicate that acid pH treatments and caprylic acid precipitations, which have been validated for the manufacture of some human IgG products, appear to provide the best potential for viral inactivation of antivenoms. As many manufacturers of antivenoms located in developing countries lack the resources to conduct formal viral validation studies, it is hoped that this review will help in the scientific understanding of the viral safety factors of antivenoms, in the controlled implementation of the manufacturing steps with expected impact on viral safety, and in the overall reinforcement of good manufacturing practices of these essential therapeutic products.

Venomous snakebites worldwide with a focus on the Australia-Pacific region: current management and controversies

Snakebites are estimated to cause approximately 100,000 deaths each year worldwide and disproportionately affect rural populations in resource-poor settings. Snake venoms may produce local tissue damage and/or distinct clinical syndromes, including neurotoxicity, coagulopathy, hypotension, rhabdomyolysis, and renal failure. Field management is aimed at delaying systemic absorption of toxins, minimizing local damage and infection, and expediting transport to medical facilities. The use of the pressure-immobilization method remains controversial. The use of antivenom, administered in a timely fashion and in adequate doses, is the mainstay of hospital treatment of significant envenomation. The availability, efficacy, and safety of antivenoms vary throughout the world, with a current crisis in antivenom supplies.

Life-threatening envenoming by the Saharan horned viper (Cerastes cerastes) causing micro-angiopathic haemolysis, coagulopathy and acute renal failure: clinical cases and review

BACKGROUND

The desert horned vipers (Cerastes cerastes and C. gasperettii) are the most familiar snakes of the great deserts of North Africa and the Middle East, including the plains of Iraq. They are responsible for many human snake bites. In Western countries, they are popular among exotic-snake keepers.

AIM

To investigate mechanisms of life-threatening envenoming and treatment.

DESIGN

Clinical investigation.

METHODS

Clinical and laboratory studies with measurement of serum venom antigen concentrations by enzyme immunoassay.

RESULTS

Two men bitten while handling captive Saharan horned vipers (Cerastes cerastes) in Europe developed extensive local swelling and life-threatening systemic envenoming, characterized by coagulopathy, increased fibrinolysis, thrombocytopenia, micro-angiopathic haemolytic anaemia and acute renal failure. The clinical picture is explicable by the presence in C. cerastes venom of several thrombin-like, Factor-X-activating, platelet-aggregating, haemorrhagic and nephrotoxic components. In one case, prophylactic use of subcutaneous epinephrine may have contributed to intracranial haemorrhage. The roles in treatment of heparin (rejected) and specific antivenom (recommended) are discussed.

DISCUSSION

Cerastes cerastes is capable of life-threatening envenoming in humans. Optimal treatment of envenoming is by early administration of specific antivenom, and avoidance of ineffective and potentially-dangerous ancillary methods.

Antibody zymography: a novel adaptation of zymography to determine the protease-neutralising potential of specific antibodies and snake antivenoms

A common problem in the development of antibody-based therapeutics is the selection, usually from a large population, of specific antibodies with the desired function. One of our research objectives is to identify antibodies capable of neutralising the most important haemorrhagic and haemostasis-disruptive proteases from viper venom. Here, we describe a modification of conventional gelatin-zymography that permits the identification of antibodies capable of neutralising gelatinolytic proteases. We demonstrate that the gelatinolytic activity of viper venom proteases is neutralised by addition of viper antivenom to the matrix of conventional gelatin-zymograms. Venom protein gelatinolytic activity was unaffected by inclusion of antibody from control, non-immunised animals or immunoglobulin-depleted serum. The application of this antibody zymogram technique for future research on snake venoms is evaluated in the context of identified limitations.

Protocol and monitoring to improve snake bite outcomes in rural Ghana

A study was conducted in Mathias Hospital, Yeji, an area of Ghana, where snake bite cases are an important cause of morbidity and mortality, with a case fatality rate of 11% (8/72). Case management difficulties included uncertainty about the assessment of the severity of envenoming, the dosage of antivenom, and the response to treatment. An intervention with several components was introduced: development of a treatment protocol, staff training, monitoring of compliance and patient education. During a 33-month post-intervention period there was excellent protocol compliance, fewer snake bite complications, and a fall in mortality rate to 1.3% (3/238) compared with a 15-month baseline review. There was a 50% increase in snake bite admissions and fewer delays. To improve snake bite outcomes in comparable settings, particularly if inexperienced staff are involved in care, we recommend a similar quality assurance project, involving case review and use of a treatment protocol with monitoring of compliance to sustain an improved approach.

Pharmacokinetic-pharmacodynamic relationships of immunoglobulin therapy for envenomation

Parenteral administration of horse- and sheep-derived antivenoms constitutes the cornerstone in the therapy of envenomations induced by animal bites and stings. Depending on the type of neutralising molecule, antivenoms are made of: (i) whole IgG molecules (150 kDa), (ii) F(ab')(2) immunoglobulin fragments (100 kDa) or (iii) Fab immunoglobulin fragments (50 kDa). Because of their variable molecular mass, these three types of antivenoms have different pharmacokinetic profiles. Fab fragments have the largest volume of distribution and readily reach extravascular compartments. They are catabolised mainly by the kidney, having a more rapid clearance than F(ab')(2) fragments and IgG. On the other hand, IgG molecules have a lower volume of distribution and a longer elimination half-life, showing the highest cycling through the interstitial spaces in the body. IgG elimination occurs mainly by extrarenal mechanisms. F(ab')(2) fragments display a pharmacokinetic profile intermediate between those of Fab fragments and IgG molecules. Such diverse pharmacokinetic properties have implications for the pharmacodynamics of these immunobiologicals, since a pronounced mismatch has been described between the pharmacokinetics of venoms and antivenoms. Some venoms, such as those of scorpions and elapid snakes, are rich in low-molecular-mass neurotoxins of high diffusibility and large volume of distribution that reach their tissue targets rapidly after injection. In contrast, venoms rich in high-molecular-mass toxins, such as those of viperid snakes, have a pharmacokinetic profile characterised by a rapid initial absorption followed by a slow absorption process from the site of venom injection. Such delayed absorption has been linked with recurrence of envenomation when antibody levels in blood decrease. This heterogeneity in pharmacokinetics and mechanism of action of venom components requires a detailed analysis of each venom-antivenom system in order to determine the most appropriate type of neutralising molecule for each particular venom. Besides having a high affinity for toxicologically relevant venom components, an ideal antivenom should possess a volume of distribution as similar as possible to that of the toxins being neutralised. Moreover, high levels of neutralising antibodies should remain in blood for a relatively prolonged time to assure neutralisation of toxins reaching the bloodstream later in the course of envenomation, and to promote redistribution of toxins from extravascular compartments to blood. Additional studies are required on different venoms and antivenoms in order to further understand the pharmacokinetic-pharmacodynamic relationships of antibodies and their fragments and to optimise the immunotherapy of envenomations.

Defibrination and systemic bleeding caused by an imported African snakebite

A 55-year-old man was referred from Burkina Fasso for coagulation disorders with severe spontaneous systemic bleeding. He had been bitten six days before by a snake that could not be definitely identified. No specific treatment had been started in Africa. The patient was admitted with severe anaemia, incoagulable blood with undetectable fibrinogen. Multiple haematomas in the chest and abdomen were found at computed tomography. Blood transfusions and the administration of fresh frozen plasma and fibrinogen did not result in any clinical or biological improvement. The clinical course was dramatically reversed after the infusion of two vials of Pasteur polyspecific antivenom (Echis-Bitis-Naja). According to the geographical distribution of this snake species, it seems very likely that the snakebite was caused by Echis ocellatus. Even given with delay, the antivenom was effective and well tolerated.

Cloning of a prothrombin activator-like metalloproteinase from the West African saw-scaled viper, Echis ocellatus

Systemic envenoming by the saw-scaled viper, Echis ocellatus, is responsible for more deaths than any other snake in West Africa. Despite its medical importance, there have been few investigations into the toxin composition of the venom of this viper. Here we describe the isolation of E. ocellatus venom gland cDNAs encoding a protein of 514 amino acids that showed 91% sequence similarity to Ecarin, a prothrombin-activating metalloproteinase from the venom of the East African viper, E. pyramidum leakeyi, that induces severe consumption coagulopathy. Structural similarities between the E. ocellatus metalloproteinase and analogues in venoms of related vipers suggest that antibodies raised to phylogenetically conserved E. ocellatus metalloproteinase domains may have potential for cross-specific and cross-generic neutralisation of analogous venom toxins.

Fractionation of equine antivenom using caprylic acid precipitation in combination with cationic ion-exchange chromatography

A combined process of caprylic acid (CA) precipitation and ion-exchange chromatography on SP-Sepharose was studied as a means to fractionate pepsin-digested horse antivenom F(ab')(2) antibody. In the CA precipitation, the optimal concentration for fractionation of F(ab')(2) from pepsin-digested horse plasma was 2%, in which 89.61% of F(ab')(2) antibody activity was recovered in the supernatant with 1.5-fold purification. A significant amount of pepsin was not precipitated and remained active under these conditions. An analytical cation exchanger Protein-Pak SP 8HR HPLC column was tested to establish optimal conditions for the effective separation of IgG, albumin, pepsin and CA from the F(ab')(2) product. From these results, the supernatant from CA precipitation of pepsin-digested plasma was subjected to a SP-Sepharose column chromatography using a linear salt gradient. With stepwise elution, a peak containing F(ab')(2) antibody could be obtained by elution with 0.25 M NaCl. The total recovery of antibody was 65.56% with 2.91-fold purification, which was higher than that achieved by ammonium sulfate precipitation. This process simultaneously and effectively removed residual pepsin, high molecular weight aggregates and CA in the final F(ab')(2) product, and should be suitable for large-scale fractionation of therapeutic equine antivenoms.

Formulation of a liquid ovine Fab-based antivenom for the treatment of envenomation by the Nigerian carpet viper (Echis ocellatus)

Most antivenoms are required for use in tropical or sub-tropical countries where temperatures may be high and refrigerated storage unavailable or unreliable. Although freeze-dried products can be expected to have maximal storage stability, many antivenoms are manufactured in liquid form to lower their cost and ease their use. We developed a liquid formulation of an existing freeze-dried antivenom against the carpet viper (Echis ocellatus) for use in Nigeria. When Fab fragments, prepared from antisera raised in sheep, were exposed to pH between 3.0 and 8.0, time and temperature dependent precipitation of some populations of the Fab product occurred over the range 4.5-7.0. Formulation of the Fab fragments in acetate buffer (20 mM) at pH 4.0 provided a clear, colourless, particle-free and stable product which retained neutralising potency for at least one year at 4 degrees C and room temperature. An accelerated study indicated stability for at least 4 weeks at 37 degrees C which may be considered equivalent to four years at 4 degrees C. The presence of sugars (sorbitol at 20 g/l or mannitol at 50 g/l) or sodium chloride (153 mM) had no effect in stabilising Fab at high temperature (37 degrees C) and, in agreement with the prediction of these accelerated studies, no beneficial effect of mannitol was found in real-time studies after one year.

Clinical toxinology--where are we now?

Clinical toxinology encompasses a broad range of medical conditions resulting from envenomation by venomous terrestrial and marine organisms, and also poisoning from ingestion of animal and plant toxins. Toxin-related disease is an important cause of morbidity and mortality worldwide, particularly in the tropical and subtropical continents. Snake bite is the single most important toxin-related disease, causing substantial mortality in many parts of Africa, Asia, and the Americas. The most important snake families are Viperidae and Elapidae, causing a range of clinical effects including local necrosis, neurotoxicity, coagulopathy and hemorrhage, myotoxicity and renal toxicity. These effects vary according to geography and group of snake. Arachnid envenomation results mainly in morbidity, particularly scorpion stings which can cause severe systemic envenomation. Spider bite is far less of a problem, and the majority of medically important cases can be attributed to widow spiders (Latrodectus spp.) and recluse spiders (Loxosceles spp.). Marine-related envenomations are common, but severe effects are less so. Plant and mushroom poisoning occur in most parts of the world, but the types and methods of poisoning vary considerably between continents. Management of toxin-related disease is often difficult, and in many cases meticulous supportive care is all that is available. The mainstay of treatment is the use of antivenoms for many envenomations and poisoning, although these do not exist for all dangerous organisms. Unfortunately antivenoms are not an economically viable product, so development and manufacture of these agents have been limited. This is now further worsened by a current shortage of antivenom. There is a need for improvement in the preventionand management of toxin-related disease. This will require well-designed studies to define the extent of the problem, initiatives to improve the prevention and management of these conditions, and development of new, and continuation of current, antivenom supplies.

A new Pan African polyspecific antivenom developed in response to the antivenom crisis in Africa

Currently there is a crisis in the supply of antivenom for treatment of snake bite in sub-Saharan Africa. Commercial pressures have resulted in the reduction or even cessation of production of antivenom by European manufacturers while continued production of antivenom in Africa has been threatened by the privatisation of the only remaining company based in Africa. As a consequence, there has been an increase in snake bite morbidity and mortality in many African countries. Two Latin American antivenom manufacturers have agreed to produce antivenom suitable for Africa, using venoms from the species which are of the greatest medical importance in sub-Saharan Africa. Preclinical in vivo assays of neutralising potency demonstrated that a new Pan African antivenom produced in Colombia compared favourably with the existing commercial monospecific and polyspecific antivenoms. This new antivenom, and a similar product being manufactured in Costa Rica, are now candidates for clinical testing at an appropriate site in Africa.

The purification and partial characterisation of two novel metalloproteinases from the venom of the West African carpet viper, Echis ocellatus

Separation of previously uncharacterised Echis ocellatus venom by phenyl-Superose FPLC (Fast Liquid Protein Chromatography) yielded eight protein fractions. Three of these displayed high proteolytic activity when assayed by in vivo and in vitro assays (including enzyme linked immunosorbant assay), and were further separated using Superdex 75 and Mono-Q FPLC. This resulted in the purification of a non-haemorrhagic 24 kDa metalloproteinase (EoVMP1, pI 7.0), and a haemorrhagic 56 kDa metalloproteinase (EoVMP2, pI 5.5). Following tryptic digest, short amino acid sequences of EoVMP1 and EoVMP2 were obtained using Edman degradation. Both sequences displayed homology when aligned with existing snake venom metalloproteinases (SVMPs). The strong homology observed among previously well-characterised SVMPs suggests that principles governing the interaction of substrates and inhibitors are likely to be similar for EoVMP1, EoVMP2 and all members of the reprolysin family.

Persistent coagulopathy in snake bite

Bleeding diathesis is a cardinal feature of viperine bite, which has been thought to last not more than 24 hours. There is scarcity of literature about prolonged bleeding disorder in snake envenomation. Various explanations suggested in the literature include-temporary decrease in antivenin levels, rapid elimination of antivenin from circulation or continuous release of unneutralised venom from the envenomated site. Two children with prolonged coagulopathy lasting for more than a week, correction of which required more than 300 ml of antisnake venom are reported here.

A protocol for 'enhanced pepsin digestion': a step by step method for obtaining pure antibody fragments in high yield from serum

The digestion of ovine antiserum under acidic conditions (pH 3.5) by pepsin is highly effective at reducing all unwanted serum components to low molecular weight (< or =13 kDa) fragments while leaving the approximately 100-kDa F(ab')(2) intact. The pH is then raised to 6 to stop further digestion and the reaction mixture centrifuged or filtered to remove any insoluble contaminants. Next, unwanted low molecular weight fragments are removed by diafiltration with a 30-kDa nominal molecular weight cut-off membrane leaving an F(ab')(2) solution contaminated only with some pepsin and a small amount of the aggregated low molecular weight fragments. Material of this purity is suitable for many applications but, since all the contaminants are highly acidic, they can be easily removed by passage down an anion-exchange column to yield F(ab')(2) that is essentially free from pepsin and aggregates with a typical purity of over 96% and yields of 16-19 g/l serum. When an antivenom was processed, approximately 78% of the original serum's toxin neutralising capacity was recovered. This simple, high yield protocol for processing serum to highly purified F(ab')(2) avoids the need for an initial or any subsequent salt precipitation step and can be utilised for either bench or large scale production. If required, a mild reducing agent may be used finally to create Fab fragments.

Intramuscular administration of antivenoms in experimental envenomation by Bothrops asper: comparison between Fab and IgG

The efficacy of intramuscular (im) administration of sheep Fab and IgG antivenoms was assessed in a mouse experimental model of envenomation by Bothrops asper, in order to test if the more rapid absorption of Fab improves neutralization. Both antivenoms were adjusted to have a similar neutralizing potency in assays involving preincubation of venom and antivenom. Neither antivenom was effective in neutralizing lethality, nor in prolonging the time of death, in mice injected with either 3, 2 or 1.5 LD(50)s of venom by the intraperitoneal (ip) route, in experiments in which antivenoms were administered im immediately after envenomation. Antivenoms were effective in the neutralization of defibrinating activity, even if treatment was performed 30 min after envenomation, with no differences between IgG and Fab. Regarding neutralization of local effects, i.e. myonecrosis and hemorrhage, im administration of antivenoms at a site distant from the venom-injection site was completely ineffective in reducing the extent of local tissue damage. However, partial neutralization of these effects was achieved if antivenoms were administered im at the same site of venom injection, provided treatment was performed immediately after envenomation. Fab antivenom was slightly more effective than IgG antivenom in the neutralization of myotoxicity under these conditions, although a similar efficacy was observed between these antivenoms regarding neutralization of hemorrhagic effect. Our observations do not evidence major differences in the neutralizing ability of Fab and IgG antivenoms when applied by the im route, and do not support the hypothesis that im administration of Fab antivenoms constitutes an effective alternative to treat B. asper envenomations.

The impact of a low dose, low volume, multi-site immunization on the production of therapeutic antivenoms in Thailand

Therapeutic antivenom against snakes was first produced by Albert Calmette in 1894. Since then antivenoms have saved the life of countless snakebite victims. However, there are still many problems associated with antivenom production, for example variable percentage of responder horses, low neutralizing potency of antivenom, the large amount of snake venom needed for immunization and the difficulties encountered in producing potent polyvalent antivenoms. These problems have led to shortage and high cost of antivenom and, in some cases, failure of treatment. In 1997, a new immunization protocol for antivenom production was reported. It involves the injection of venom at low dose (approx. 2mg/horse) emulsified in Complete Freund's adjuvant in low volume (0.1-0.2 ml/site) in a total of 10 sites around the neck area of the horse. This immunization protocol has minimized the local reaction at the injection site thus allowing the use of the potent oil adjuvant. This, together with the increase in total surface area of the droplets, allow a more effective immune response to take place, e.g. enhancing the migration and activation of more antigen presenting cells and lymphocytes. The low dose, low volume multi-site immunization has resulted in dramatic improvements on the antivenom production in terms of amount of venom used for immunization, the time required to reach hyperimmune stage, the percent of responder horses and the potency of the antivenom. Furthermore, this protocol has made it possible to produce potent truly polyvalent antivenoms against several elapid and viperid snakes. This immunization protocol has alleviated various problems associated with antivenom production and has implications for immunization in general.

Immediate and delayed allergic reactions to Crotalidae polyvalent immune Fab (ovine) antivenom

Allergic reactions are the most commonly reported adverse events after administration of antivenoms. Conventional horse serum-based crotalid antivenom used in the United States (Antivenin [Crotalidae] polyvalent) can lead to both immediate and delayed hypersensitivity reactions. Crotalidae polyvalent immune Fab (ovine) (CroFab; FabAV) has recently been approved for use in the United States. Experience from premarketing trials of this product and in the administration of other types of Fab, such as in digoxin poisoning, has demonstrated these fragments to be safe and effective, with a low incidence of sequella; however, allergic reactions can occur when any animal-protein derivatives are administered to human subjects. We report in detail the nature and course of allergic reactions that occurred in 4 patients treated with FabAV. Cases of anaphylaxis, acute urticaria, angioedema, and delayed serum sickness are described. All reactions were easily treated with some combination of antihistamines, epinephrine, and steroids, with prompt resolution of signs and symptoms enabling further dosing of antivenom as required. Several of these cases may have resulted from batches of antivenom contaminated with Fc fragments. The overall incidence of immediate and delayed allergic reactions to this product appears so far to be lower than that reported with conventional whole-immunoglobulin G (IgG) antivenom, but postmarketing surveillance is warranted.

Effect of preservatives on IgG aggregation, complement-activating effect and hypotensive activity of horse polyvalent antivenom used in snakebite envenomation

Intravenous administration of antivenoms is associated with early adverse reactions in a number of cases, but the causes of this phenomenon are still unclear. The effect of preservatives (phenol and thimerosal) on IgG aggregate and dimer formation, in vitro complement-activating effect and hypotensive activity of a whole IgG horse liquid polyvalent antivenom, produced by caprylic acid fractionation, was assessed. These parameters were studied since they have been associated with the development of early adverse reactions to the administration of antivenoms and human immunoglobulins. After a three-year storage period at 4 degrees C, antivenoms with preservatives had an increased content of IgG aggregates and dimers when compared with antivenom devoid of phenol and thimerosal. These observations correlate with a slight increment in the turbidity of preservative-containing antivenoms. The three antivenoms studied (formulation: no preservatives; with phenol and thimerosal; with thimerosal alone) activated human complement in vitro, with only minor quantitative differences among them. When antivenoms were administered as a bolus intravenous injection in rats, a rapid and prominent hypotension of short duration was observed after injection of phenol-containing antivenom, whereas such an effect was absent in antivenom free of preservative and in the one containing only thimerosal. Bolus injection of saline solution with phenol resulted in a similar hypotension, indicating that the effect is due to phenol. However, when phenol-containing antivenom was diluted 1:5 with saline solution before infusion, as occurs in the clinical use of this product, no hypotension was observed. Our results stress the need to evaluate the effects of preservatives on the physicochemical and pharmacological characteristics of antivenoms.