An examination of the activity of expired and mistreated commercial Australian antivenoms

Anticoagulant activity in Australasian elapid snake venoms and neutralisation with antivenom and varespladib

The venoms of Australasian elapid snakes are known to possess coagulant activity, including some with strong procoagulant activity and others with anticoagulant activity, although the latter are less well known. This study investigates the anticoagulant activity of Australasian elapid snake venoms, and whether this activity is neutralised by commercial snake antivenom and varespladib (PLA2 inhibiting agent). Clotting assays were completed for 34 species of Australasian elapids. Antivenom neutralisation assays with tiger snake antivenom (TSAV) were performed on five species to determine if there was cross-neutralisation. Varespladib neutralisation assays were also completed for the same five species. All Pseudechis species venoms had anticoagulant activity, except P. porphyriacus, which was procoagulant. Pseudechis species venoms had similar anticoagulant potency ranging from the most potent P. colletti venom to the least potent P. butleri venom. The three Austrelaps (copperhead) species venoms were the next most potent anticoagulants. Six further snakes, Elapognathus coronatus, Acanthophis pyrrhus, A. antarcticus, Suta suta, Denisonia devisi and D. maculata, had weaker anticoagulant activity, except for D. maculata which had similar anticoagulant activity to Pseudechis species. Tiger Snake Antivenom (1200mU/mL) neutralised the anticoagulant effect of P. australis for concentrations up to 1 mg/mL. TSAV (1200mU/mL) also neutralised P. colletti, D. maculata, A. superbus and A. pyrrhus venoms at their EC50, demonstrating cross neutralisation. Varespladib neutralised the anticoagulant effect of P. australis venom at 5 μM and for venoms of P. colletti, D. maculata, A. superbus and A. pyrrhus. We found anticoagulant activity to be present in six genera of Australasian snakes at low concentrations, which can be completely neutralised by both antivenom and varespladib. Anticoagulant activity in Australian elapid venoms was associated with species possessing high PLA2 activity without procoagulant snake venom serine proteases.

Fangs and foliage: Unearthing the haemotoxic secrets of cannabis-dwelling rattlesnakes

Despite a recent surge in high-throughput venom research that has enabled many species to be studied, some snake venoms remain understudied. The long-tailed rattlesnakes (Crotalus ericsmithi, C. lannomi, and C. stejnegeri) are one group where such research lags, largely owing to the rarity of these snakes and the hazardous areas, ripe with drug (marijuana and opium) production, they inhabit in Mexico. To fill this knowledge gap, we used multiple functional assays to examine the coagulotoxic (including across different plasma types), neurotoxic, and myotoxic activity of the venom of the long-tailed rattlesnakes. All crude venoms were shown to be potently anticoagulant on human plasma, which we discovered was not due to the destruction of fibrinogen, except for C. stejnegeri displaying minor fibrinogen destruction activity. All venoms exhibited anticoagulant activity on rat, avian, and amphibian plasmas, with C. ericsmithi being the most potent. We determined the mechanism of anticoagulant activity by C. ericsmithi and C. lannomi venoms to be phospholipid destruction and inhibition of multiple coagulation factors, leading to a net disruption of the clotting cascade. In the chick biventer assay, C. ericsmithi and C. lannomi did not exhibit neurotoxic activity but displayed potential weak myotoxic activity. BIRMEX® (Faboterápico Polivalente Antiviperino) antivenom was not effective in neutralising this venom effect. Overall, this study provides an in-depth investigation of venom function of understudied long-tailed rattlesnakes and provides a springboard for future venom and ecology research on the group.

African polyvalent antivenom can maintain pharmacological stability and ability to neutralise murine venom lethality for decades post-expiry: evidence for increasing antivenom shelf life to aid in alleviating chronic shortages

INTRODUCTION

Antivenom is a lifesaving medicine for treating snakebite envenoming, yet there has been a crisis in antivenom supply for many decades. Despite this, substantial quantities of antivenom stocks expire before use. This study has investigated whether expired antivenoms retain preclinical quality and efficacy, with the rationale that they could be used in emergency situations when in-date antivenom is unavailable.

METHODS

Using WHO guidelines and industry test requirements, we examined the in vitro stability and murine in vivo efficacy of eight batches of the sub-Saharan African antivenom, South African Institute for Medical Research polyvalent, that had expired at various times over a period of 30 years.

RESULTS

We demonstrate modest declines in immunochemical stability, with antivenoms older than 25 years having high levels of turbidity. In vitro preclinical analysis demonstrated all expired antivenoms retained immunological recognition of venom antigens and the ability to inhibit key toxin families. All expired antivenoms retained comparable in vivo preclinical efficacy in preventing the lethal effects of envenoming in mice versus three regionally and medically important venoms.

CONCLUSIONS

This study provides strong rationale for stakeholders, including manufacturers, regulators and health authorities, to explore the use of expired antivenom more broadly, to aid in alleviating critical shortages in antivenom supply in the short term and the extension of antivenom shelf life in the longer term.

Experience of using expired lyophilized snake antivenom during a medical emergency situation in Lao People's Democratic Republic--A possible untapped resource to tackle antivenom shortage in Southeast Asia

OBJECTIVES

To evaluate the safety and efficacy of expired lyophilized snake antivenom of Thai origin during a medical emergency in 2020/2021 in Lao People's Democratic Republic.

METHODS

Observational case series of patients with potentially life-threatening envenoming who consented to the administration of expired antivenom between August 2020 and May 2022.

RESULTS

A total of 31 patients received the expired antivenom. Malayan pit vipers (Calloselasma rhodostoma) were responsible for 26 (84%) cases and green pit vipers (Trimeresurus species) for two cases (6%). In three patients (10%) the responsible snake could not be identified. Of these, two presented with signs of neurotoxicity and one with coagulopathy. A total of 124 vials of expired antivenom were administered. Fifty-nine vials had expired 2-18 months earlier, 56 vials 19-36 months and nine vials 37-60 months before. Adverse effects of variable severity were observed in seven (23%) patients. All 31 patients fully recovered from systemic envenoming.

CONCLUSIONS

Under closely controlled conditions and monitoring the use of expired snake antivenom proved to be effective and safe. Discarding this precious medication is an unnecessary waste, and it could be a valuable resource in ameliorating the current shortage of antivenom. Emergency use authorization granted by health authorities and preclinical testing of expired antivenoms could provide the support and legal basis for such an approach.

In Vitro Neutralization of the Myotoxicity of Australian Mulga Snake (Pseudechis australis) and Sri Lankan Russell's Viper (Daboia russelii) Venoms by Australian and Indian Polyvalent Antivenoms

We studied the neutralisation of Sri Lankan Russell's viper (Daboia russelii) and Australian mulga snake (Pseudechis australis) venom-induced myotoxicity by Indian (Vins and Bharat) and Australian (Seqirus) polyvalent antivenoms, using the in vitro chick biventer skeletal muscle preparation. Prior addition of Bharat or Vins antivenoms abolished D. russelii venom (30 µg/mL)-mediated inhibition of direct twitches, while Australian polyvalent antivenom was not protective. Bharat antivenom prevented, while Vins and Australian polyvalent antivenoms partially prevented, the inhibition of responses to exogenous KCl. Myotoxicity of Mulga venom (10 µg/mL) was fully neutralised by the prior addition of Australian polyvalent antivenom, partially neutralised by Vins antivenom but not by Bharat antivenom. Although the myotoxicity of both venoms was partially prevented by homologous antivenoms when added 5 min after the venom, with an increasing time delay between venom and antivenom, the reversal of myotoxicity gradually decreased. However, antivenoms partially prevented myotoxicity even 60 min after venom. The effect of antivenoms on already initiated myotoxicity was comparable to physical removal of the toxins by washing the bath at similar time points, indicating that the action of the antivenoms on myotoxicity is likely to be due to trapping the toxins or steric hindrance within the circulation, not allowing the toxins to reach target sites in muscles.

Cross-reactivity of some Micrurus venoms against experimental and therapeutic anti-Micrurus antivenoms

We developed experimental equine polyvalent and monovalent antivenoms against the venoms of Micrurus (M.) fulvius, M. nigrocinctus and M. surinamensis and studied their immunochemical reactivity on the venoms used as immunogens and on M. pyrrhocryptus, M altirostris and M. balyocoriphus venoms. Assessment of the neutralizing capacity of the polyvalent experimental antivenom was based on inhibition of lethality (preincubation and rescue assay experiments in mice) and indirect hemolytic and phospholipase activities. The immunochemical reactivity and neutralizing capacity were compared with those of two therapeutic antivenoms used for the treatment of coral snake envenomation in North America and in Argentina. In general, the experimental antivenom conferred a comparable level of neutralization against the venoms used as immunogens when compared to the therapeutic antivenoms and a certain level of cross-neutralization against the other venoms. The results suggest the need for additional venoms in the immunogenic mixture used, in order to obtain a broad spectrum anti-Micrurus antivenom with a good neutralizing potency. Paraspecific neutralization of South American coral snake venoms, although present at a higher level than the neutralization conferred by available nonspecific Micrurus therapeutic antivenoms, was rather low in relation to the specific neutralizing capacity.

What is the impact of snakebite envenoming on domestic animals? A nation-wide community-based study in Nepal and Cameroon

Snakebite envenoming is a life-threatening disease in humans and animals and a major public health issue in rural communities of South-East Asia and sub-Saharan Africa. Yet the impact of snakebite on domestic animals has been poorly studied. This study aimed to describe the context, clinical features, treatment, and outcomes of snakebite envenoming in domestic animals in Nepal and Cameroon. Primary data on snakebite in animals were recorded from a community-based nation-wide survey on human and animal snakebite in Nepal and Cameroon (Snake-byte project). Mobile teams collected data on snakebite in humans and animals in 13,879 and 10,798 households in Nepal and Cameroon respectively from December 2018 to June 2019. This study included 405 snakebite cases (73 in Nepal and 332 in Cameroon) in multiple types of animals. An interview with a structured questionnaire collected specific information about the animal victims. Snake bites in animals took place predominantly inside and around the house or farm in Nepal (92%) and Cameroon (71%). Other frequent locations in Cameroon were field or pasture (12%). A large diversity of clinical features was reported in all types of envenomed animals. They showed either a few clinical signs (e.g., local swelling, bleeding) or a combination of multiple clinical signs. Only 9% of animal victims, mainly cattle and buffaloes and less frequently goats, sheep, and dogs, received treatment, predominantly with traditional medicine. The overall mortality of snakebite was 85% in Nepal and 87% in Cameroon. Results from this nationwide study show an important impact of snakebite on animal health in Nepal and Cameroon. There is a need for cost-effective prevention control strategies and affordable snakebite therapies in the veterinary field to save animal lives and farmer livelihood in the poorest countries of the world. The WHO global strategy to prevent and control snakebite envenoming supports a One Health approach, which may help develop integrated solutions to the snakebite problem taking into account human and animal health.

Clinical implications of ontogenetic differences in the coagulotoxic activity of Bothrops jararacussu venoms

Is snake venom activity influenced by size? This is a long-standing question that can have important consequences for the treatment of snake envenomation. Ontogenetic shifts in venom composition are a well-documented characteristic of numerous snake species. Although snake venoms can cause a range of pathophysiological disturbances, establishing the coagulotoxic profiles related to such shifts is a justified approach because coagulotoxicity can be deadly, and its neutralisation is a challenge for current antivenom therapy. Thus, we aimed to assess the coagulotoxicity patterns on plasma and fibrinogen produced by B othrops jararacussu venoms from individuals of different sizes and sex, and the neutralisation potential of SAB (anti bothropic serum produced by Butantan Institute). The use of a metalloproteinase inhibitor (Prinomastat) and a serine proteinase inhibitor (AEBSF) enabled us to determine the toxin class responsible for the observed coagulopathy: activity on plasma was found to be metalloprotease driven, while the activity on fibrinogen is serine protease driven. To further explore differences in venom activity, the activation of Factor X and prothrombin as a function of snake size was also evaluated. All the venoms exhibited a potent procoagulant effect upon plasma and were less potent in their pseudo-procoagulant clotting effect upon fibrinogen. On human plasma, the venoms from smaller snakes produced more rapid clotting than the larger ones. In contrast, the venom activity on fibrinogen had no relation with size or sex. The difference in procoagulant potency was correlated with the bigger snakes being proportionally better neutralized by antivenom due to the lower levels of procoagulant toxins, than the smaller. Thus, while the antivenom ultimately neutralized the venoms, proportionally more would be needed for an equal mass of venom from a small snake than a large one. Similarly, the neutralisation by SAB of the pseudo-procoagulant clotting effects was also correlated with relative potency, with the smaller and bigger snakes being neutralized proportional to potency, but with no correlation to size. Thromboelastography (TEG) tests on human and toad plasma revealed that small snakes' venoms acted quicker than large snakes' venom on both plasmas, with the action upon amphibian plasma consistent with smaller snakes taking a larger proportion of anuran prey than adults. Altogether, the ontogenetic differences regarding coagulotoxic potency and corresponding impact upon relative antivenom neutralisation of snakes with different sizes were shown, underscoring the medical importance of investigating ontogenetic changes in order to provide data crucial for evidence-based design of clinical management strategies.

A Clot Twist: Extreme Variation in Coagulotoxicity Mechanisms in Mexican Neotropical Rattlesnake Venoms

Rattlesnakes are a diverse clade of pit vipers (snake family Viperidae, subfamily Crotalinae) that consists of numerous medically significant species. We used validated in vitro assays measuring venom-induced clotting time and strength of any clots formed in human plasma and fibrinogen to assess the coagulotoxic activity of the four medically relevant Mexican rattlesnake species Crotalus culminatus, C. mictlantecuhtli, C. molossus, and C. tzabcan. We report the first evidence of true procoagulant activity by Neotropical rattlesnake venom in Crotalus culminatus. This species presented a strong ontogenetic coagulotoxicity dichotomy: neonates were strongly procoagulant via Factor X activation, whereas adults were pseudo-procoagulant in that they converted fibrinogen into weak, unstable fibrin clots that rapidly broke down, thereby likely contributing to net anticoagulation through fibrinogen depletion. The other species did not activate clotting factors or display an ontogenetic dichotomy, but depleted fibrinogen levels by cleaving fibrinogen either in a destructive (non-clotting) manner or via a pseudo-procoagulant mechanism. We also assessed the neutralization of these venoms by available antivenom and enzyme-inhibitors to provide knowledge for the design of evidence-based treatment strategies for envenomated patients. One of the most frequently used Mexican antivenoms (Bioclon Antivipmyn®) failed to neutralize the potent procoagulant toxic action of neonate C. culminatus venom, highlighting limitations in snakebite treatment for this species. However, the metalloprotease inhibitor Prinomastat substantially thwarted the procoagulant venom activity, while 2,3-dimercapto-1-propanesulfonic acid (DMPS) was much less effective. These results confirm that venom-induced Factor X activation (a procoagulant action) is driven by metalloproteases, while also suggesting Prinomastat as a more promising potential adjunct treatment than DMPS for this species (with the caveat that in vivo studies are necessary to confirm this potential clinical use). Conversely, the serine protease inhibitor 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride (AEBSF) inhibited the direct fibrinogen cleaving actions of C. mictlantecuhtli venom, thereby revealing that the pseudo-procoagulant action is driven by kallikrein-type serine proteases. Thus, this differential ontogenetic variation in coagulotoxicity patterns poses intriguing questions. Our results underscore the need for further research into Mexican rattlesnake venom activity, and also highlights potential limitations of current antivenom treatments.

Pan-American Lancehead Pit-Vipers: Coagulotoxic Venom Effects and Antivenom Neutralisation of Bothrops asper and B. atrox Geographical Variants

The toxin composition of snake venoms and, thus, their functional activity, can vary between and within species. Intraspecific venom variation across a species’ geographic range is a major concern for antivenom treatment of envenomations, particularly for countries like French Guiana that lack a locally produced antivenom. Bothrops asper and Bothrops atrox are the most medically significant species of snakes in Latin America, both producing a variety of clinical manifestations, including systemic bleeding. These pathophysiological actions are due to the activation by the venom of the blood clotting factors Factor X and prothrombin, thereby causing severe consumptive coagulopathy. Both species are extremely wide-ranging, and previous studies have shown their venoms to exhibit regional venom variation. In this study, we investigate the differential coagulotoxic effects on human plasma of six venoms (four B. asper and two B. atrox samples) from different geographic locations, spanning from Mexico to Peru. We assessed how the venom variation of these venom samples affects neutralisation by five regionally available antivenoms: Antivipmyn, Antivipmyn-Tri, PoliVal-ICP, Bothrofav, and Soro Antibotrópico (SAB). The results revealed both inter- and intraspecific variations in the clotting activity of the venoms. These variations in turn resulted in significant variation in antivenom efficacy against the coagulotoxic effects of these venoms. Due to variations in the venoms used in the antivenom production process, antivenoms differed in their species-specific or geographical neutralisation capacity. Some antivenoms (PoliVal-ICP, Bothrofav, and SAB) showed species-specific patterns of neutralisation, while another antivenom (Antivipmyn) showed geographic-specific patterns of neutralisation. This study adds to current knowledge of Bothrops venoms and also illustrates the importance of considering evolutionary biology when developing antivenoms. Therefore, these results have tangible, real-world implications by aiding evidence-based design of antivenoms for treatment of the envenomed patient. We stress that these in vitro studies must be backed by future in vivo studies and clinical trials before therapeutic guidelines are issued regarding specific antivenom use in a clinical setting.

Anticoagulant Micrurus venoms: Targets and neutralization

Snakebite is a neglected tropical disease with a massive global burden of injury and death. The best current treatments, antivenoms, are plagued by a number of logistical issues that limit supply and access in remote or poor regions. We explore the anticoagulant properties of venoms from the genus Micrurus (coral snakes), which have been largely unstudied, as well as the effectiveness of antivenom and a small-molecule phospholipase inhibitor-varespladib-at counteracting these effects. Our in vitro results suggest that these venoms likely interfere with the formation or function of the prothrombinase complex. We find that the anticoagulant potency varies widely across the genus and is especially pronounced in M. laticollaris. This variation does not appear to correspond to previously described patterns regarding the relative expression of the three-finger toxin and phospholipase A₂ (PLA₂) toxin families within the venoms of this genus. The coral snake antivenom Coralmyn, is largely unable to ameliorate these effects except for M. ibiboboca. Varespladib on the other hand completely abolished the anticoagulant activity of every venom. This is consistent with the growing body of results showing that varespladib may be an effective treatment for a wide range of toxicity caused by PLA₂ toxins from many different snake species. Varespladib is a particularly attractive candidate to help alleviate the burden of snakebite because it is an approved drug that possesses several logistical advantages over antivenom including temperature stability and oral availability.

Anticoagulant activity of black snake (Elapidae: Pseudechis) venoms: Mechanisms, potency, and antivenom efficacy

Venoms from Pseudechis species (Australian black snakes) within the Elapidae family are rich in anticoagulant PLA2 toxins, with the exception of one species (P. porphyriacus) that possesses procoagulant mutated forms of the clotting enzyme Factor Xa. Previously the mechanism of action of the PLA2 toxins' anticoagulant toxicity was said to be due to inhibition of Factor Xa, but this statement was evidence free. We conducted a series of anticoagulation assays to elucidate the mechanism of anticoagulant action produced by P. australis venom. Our results revealed that, rather than targeting FXa, the PLA2 toxins inhibited the prothrombinase complex, with FVa-alone or as part of the prothrombinase complex-as the primary target; but with significant thrombin inhibition also noted. In contrast, FXa, and other factors inhibited only to a lesser degree were minor targets. We quantified coagulotoxic effects upon human plasma caused by all nine anticoagulant Pseudechis species, including nine localities of P. australis across Australia, and found similar anticoagulant potency across all Pseudechis species, with greater potency in P. australis and the undescribed Pseudechis species in the NT. In addition, the northern localities and eastern of P. australis were significantly more potent than the central, western, and southern localities. All anticoagulant venoms responded well to Black Snake Antivenom, except P. colletti which was poorly neutralised by Black Snake Antivenom and also Tiger Snake Antivenom (the prescribed antivenom for this species). However, we found LY315920 (trade name: Varespladib), a small molecule inhibitor of PLA2 proteins, exhibited strong potency against P. colletti venom. Thus, Varespladib may be a clinically viable treatment for anticoagulant toxicity exerted by this species that is not neutralised by available antivenoms. Our results provide insights into coagulotoxic venom function, and suggest future in vivo work be conducted to progress the development of a cheaper, first-line treatment option to treat PLA2-rich snake venoms globally.

The neutralization efficacy of expired polyvalent antivenoms: An alternative option

The expense of production and distribution of snakebite antivenom, as well as its relatively infrequent use, has caused antivenom to be increasingly difficult to obtain and ultimately producing an alarming global shortage. Unused, expired antivenom may represent a significant, untapped resource to ameliorate this crisis. This study examines the efficacy of expired antivenom over time using in vitro, whole blood clotting, and platelet function statistics. Representatives from three years for four different global brands of polyvalent antivenom were chosen and tested against their corresponding venoms as well as other venoms that could display cross-reactivity. These antivenoms include Wyeth Polyvalent (U.S.; exp. 1997, 2001, 2003), Antivipmyn^® (Mexico; exp. 2005, 2013, 2017), Biotecfars Polyvalent (Venezuela; exp. 2010, 2014, 2016), and SAIMR (South Africa; exp. 1997, 2005, 2017). Venoms of species tested were Crotalus atrox against Wyeth; C. atrox and Crotalus vegrandis against Antivipmyn^®; C. atrox, C. vegrandis and Bothrops colombiensis against Biotecfar; and Bitis gabonica and Echis carinatus against South African Institute for Medical Research (SAIMR). Parameters recorded were activated clotting time (ACT), clotting rate (CR), and platelet function (PF). Preliminary results are encouraging as the antivenoms maintained significant efficacy even 20 y after their expiration date. We anticipate these results will motivate further studies and provide hope in the cases of snakebite emergencies when preferable treatments are unavailable.

The Urgent Need to Develop Novel Strategies for the Diagnosis and Treatment of Snakebites

Snakebite envenoming (SBE) is a priority neglected tropical disease, which kills in excess of 100,000 people per year. Additionally, many millions of survivors also suffer through disabilities and long-term health consequences. The only treatment for SBE, antivenom, has a number of major associated problems, not least, adverse reactions and limited availability. This emphasises the necessity for urgent improvements to the management of this disease. Administration of antivenom is too frequently based on symptomatology, which results in wasting crucial time. The majority of SBE-affected regions rely on broad-spectrum polyvalent antivenoms that have a low content of case-specific efficacious immunoglobulins. Research into small molecular therapeutics such as varespladib/methyl-varespladib (PLA2 inhibitors) and batimastat/marimastat (metalloprotease inhibitors) suggest that such adjunctive treatments could be hugely beneficial to victims. Progress into toxin-specific monoclonal antibodies as well as alternative binding scaffolds such as aptamers hold much promise for future treatment strategies. SBE is not implicit during snakebite, due to venom metering. Thus, the delay between bite and symptom presentation is critical and when symptoms appear it may often already be too late to effectively treat SBE. The development of reliable diagnostical tools could therefore initiate a paradigm shift in the treatment of SBE. While the complete eradication of SBE is an impossibility, mitigation is in the pipeline, with new treatments and diagnostics rapidly emerging. Here we critically review the urgent necessity for the development of diagnostic tools and improved therapeutics to mitigate the deaths and disabilities caused by SBE.

Review article: Let us talk about snakebite management: A discussion on many levels

We want to discuss antivenom use in snakebite clinical practice guidelines. Coronial reviews in Victoria of two cases of snakebite envenomation, one described in detail below, prompted us to submit this paper for a wider audience and debate. Venom and antivenom levels were measured in the case detailed below, but not in the other. The coroner received conflicting and varied advice from experts regarding the dose of antivenom. The Victorian Department of Health and Human Services and the Australasian College for Emergency Medicine were instructed to review snakebite management guidelines, particularly with respect to antivenom dosage. The discussion that took place among medical experts led to considerable media attention. We discuss the potential fallout when there is no consensus among medical experts.

Evaluating the physicochemical properties and efficacy of recently expired and aged antivenom products from Thailand and Taiwan

Gel filtration chromatography and gel electrophoresis revealed minimal protein degradation in lyophilized antivenoms which were 2-year expired (Hemato Polyvalent, Neuro Polyvalent; Thailand) and 18-year expired (Hemato Bivalent, Neuro Bivalent; Taiwan). All expired antivenoms retained immunological binding activity, and were able to neutralize the hemotoxic or neurotoxic as well as lethal effects of the homologous snake venoms. The findings show that antivenoms under proper storage conditions may remain relatively stable beyond the indicated shelf life.

Catch a tiger snake by its tail: Differential toxicity, co-factor dependence and antivenom efficacy in a procoagulant clade of Australian venomous snakes

A paradigm of venom research is adaptive evolution of toxins as part of a predator-prey chemical arms race. This study examined differential co-factor dependence, variations relative to dietary preference, and the impact upon relative neutralisation by antivenom of the procoagulant toxins in the venoms of a clade of Australian snakes. All genera were characterised by venoms rich in factor Xa which act upon endogenous prothrombin. Examination of toxin sequences revealed an extraordinary level of conservation, which indicates that adaptive evolution is not a feature of this toxin type. Consistent with this, the venoms did not display differences on the plasma of different taxa. Examination of the prothrombin target revealed endogenous blood proteins are under extreme negative selection pressure for diversification, this in turn puts a strong negative selection pressure upon the toxins as sequence diversification could result in a drift away from the target. Thus this study reveals that adaptive evolution is not a consistent feature in toxin evolution in cases where the target is under negative selection pressure for diversification. Consistent with this high level of toxin conservation, the antivenom showed extremely high-levels of cross-reactivity. There was however a strong statistical correlation between relative degree of phospholipid-dependence and clotting time, with the least dependent venoms producing faster clotting times than the other venoms even in the presence of phospholipid. The results of this study are not only of interest to evolutionary and ecological disciplines, but also have implications for clinical toxinology.

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

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

Towards rationalisation of antivenom use in funnel-web spider envenoming: enzyme immunoassays for venom concentrations

CONTEXT

Funnel-web spider (Atrax and Hadronyche spp.) envenoming is rare but causes severe neuromuscular, autonomic, and cardiac effects. A rabbit-derived IgG antivenom is available, but venom detection in patients has not been reported.

OBJECTIVE

To use serial venom and antivenom concentrations to better define envenoming and antivenom effectiveness.

MATERIALS AND METHODS

Serum was collected from nine patients with suspected funnel-web spider bites and clinical effects were recorded. Venom-specific enzyme immunoassays were developed to measure funnel-web spider venom and antivenom concentrations. Goat anti-rabbit whole serum was coupled to UltraLink resin and added to samples to remove bound venom and measure free venom. Antivenom efficacy was defined as antivenom binding all free venom and antivenom effectiveness as resolution of clinical features.

RESULTS

Venom was detectable in samples from six of nine patients. In three patients without venom detected, there were only moderate effects, which did not completely respond to antivenom in all cases and no spider was identified. In five of six cases, a male Atrax spp. (Sydney funnel-web) spider was identified. Three patients had moderate envenoming which responded to antivenom. Three patients had severe envenoming and developed catecholamine-induced myocarditis and acute pulmonary oedema. Although cholinergic and non-specific clinical features appeared to respond to antivenom, myocarditis and pulmonary oedema lasted 2-4 days. Median venom concentration pre-antivenom in five patients with samples was 5.6 ng/ml (3-35 ng/ml), and immediately post-antivenom decreased to a median of 0 ng/ml (0-1.8 ng/ml). Post-antivenom venom concentrations decreased when bound venom was removed; median, 0 ng/ml (0-0.9 ng/ml), indicating that most venom detected post-antivenom was bound. There was recurrence of venom and clinical features in one patient when a pressure bandage was removed.

CONCLUSIONS

Detection of venom in suspected funnel-web spider bites identified definite cases with characteristic envenoming and a spider was identified. Measurement of venom concentrations pre- and post-antivenom demonstrated that venom was bound by antivenom, but in severe cases cardiac toxicity was not reversed.

Establishment and first experiences of the National Serum Depot in the Netherlands

Since 2008, a National Serum Depot is operational in the Netherlands, guaranteeing antivenom supply, 24 h per day, during medical emergencies. In this article the organisation structure, choice of antivenoms, problems encountered during the establishment, and the results from establishment in 2008 till December 2011 are discussed. The Serum Depot is organised by the National Institute for Public Health and the Environment in cooperation with the Dutch National Poisons Information Center. During establishing and maintaining of the Serum Depot several antivenom purchase difficulties were encountered. Some antivenom producers did not respond upon (initial) contact and some antivenoms were (temporarily) unavailable. Good contacts with professional herpetologists are necessary in order to keep the content of the depot up-to-date. At the same time, it is important to remain well informed concerning the safety and efficacy of the currently available antivenoms and development of new antivenoms. During the first four years of the National Serum Depot, the Dutch National Poisons Information Center was consulted on average 10 times a year about exotic venomous bites and stings in which antivenom treatment might play a role. Almost half of these consultations were related to bites by venomous exotic snakes, the other half to scorpion and fish stings. Antivenom was delivered in five cases, all after a bite by an exotic venomous snake, and actually administered twice because of the severity of local effects. To reduce costs and extend coverage of the Serum Depot of antivenoms for more unfamiliar snake species, international cooperation between the various owners of the antivenom Serum Depots in Europe is recommended.