Expanding the neutralization scope of the Central American antivenom (PoliVal-ICP) to include the venom of Crotalus durissus pifanorum

Venom composition, toxicity and cross-neutralization by PoliVal-ICP antivenom, of Mesoamerican jumping pitvipers genus Metlapilcoatlus (Viperidae: Crotalinae)

BACKGROUND

The genus Metlapilcoatlus was recently erected to include six species of stout venomous snakes, known as the jumping pitvipers, which inhabit mountainous areas of Mesoamerica. This group maintains affinity with Atropoides picadoi, another jumping pitviper with restricted distribution in Costa Rica and Panama. Although the venom of A. picadoi and a couple of Metlapilcoatlus species has previously been characterized, little is known about the interspecific and intraspecific variation of the other species that comprise the genus. In this work, we characterize the venoms of five out of the six species that make up the genus Metlapilcoatlus: Metlapilcoatlus indomitus, Metlapilcoatlus mexicanus, Metlapilcoatlus nummifer, Metlapilcoatlus occiduus and Metlapilcoatlus olmec, and for three of them, we analyze whether ontogenetic change occurs in the composition of their venoms. Additionally, we evaluated the cross-neutralizing capacity of the antivenom PoliVal-ICP used in Central American countries to treat viper envenomation.

METHODS

We utilized sodium dodecyl sulfate-polyacrylamide gel electrophoresis and reverse-phase HPLC for venom characterization. Toxin identification was conducted using a bottom-up shotgun proteomic approach. We also estimated venom toxicity based on average lethality estimates in a murine model. The PoliVal-ICP neutralizing capacity on lethal activity was evaluated for all venoms. Using the venom of M. mexicanus as a model, we also tested the neutralizing capacity of this antivenom on hemorrhagic, myotoxic, proteolytic, phospholipase and coagulant activities.

RESULTS

Our analysis revealed that the venoms of jumping vipers are composed of proteins belonging to approximately 8-17 families, typically shared with other crotalines. Despite these general similarities, we observed variations at both intraspecific, including ontogenetic, and interspecific levels in venom composition and toxicity. The chromatographic pattern of Metlapilcoatlus venom exhibited peaks in the PLA2/PLA2-like eluting region, likely responsible for the myotoxic activity of these venoms. By contrast, these peaks were almost negligible in the chromatogram of A. picadoi, whose venom is significantly more hemorrhagic. Among the Metlapilcoatlus species, M. indomitus venom stood out as notably different from the others, and it was also the most lethal. The antivenom demonstrated its effectiveness in neutralizing the lethal activity of all the venoms tested, as well as the various biological activities studied in the venom of M. mexicanus.

CONCLUSIONS

Beyond the scope of the variation revealed here, our preclinical results demonstrate that PoliVal-ICP antivenom effectively neutralizes toxins from the venom of all Mesoamerican jumping vipers, despite not including venom from any of them in its immunization mixture. This cross-neutralization capacity predicts ICP antivenom's effectiveness in treating snake envenoming in the Neotropical region.

A polygeneric immunogen composed of 22 venoms from sub-Saharan African snakes to expand the neutralization scope of the EchiTAb-plus-ICP antivenom

Recent research suggests that a polygeneric immunogen made from the venoms of the most medically important viperid and elapid snakes in sub-Saharan Africa could elicit a broader antibody response in horses compared to the current EchiTAb-plus-ICP antivenom, especially against neurotoxic elapid venoms. To test this, 25 horses that have been regularly immunized to produce this antivenom were reimmunized with an immunogen containing 22 venoms from various snake species from the genera Bitis, Echis, Dendroaspis, and both spitting and non-spitting Naja. The plasma collected from these horses was processed using the caprylic acid method to produce an industrial-scale freeze-dried antivenom. The anti-lethal neutralization scope of this new formulation was then compared to that of EchiTAb-plus-ICP which is designed to target the venoms of Bitis arietans, Echis ocellatus, Naja nigricollis, and Dendroaspis polylepis. The results indicated that adding more venoms to the immunogen did not significantly enhance the neutralization of the lethal effect of viperid venoms (except for Bitis nasicornis) or of venoms of spitting cobras (except for Naja katiensis). However, incorporating additional venoms from non-spitting neurotoxic Naja spp. and Dendroaspis spp. improved the neutralization scope of EchiTAb-plus-ICP against these neurotoxic venoms. The antivenom generated showed a wider anti-lethal neutralizing scope, as compared to the standard EchiTAb-plus-ICP antivenom and constitutes a good candidate to be tested in clinical trials in sub-Saharan Africa.

Stress levels, hematological condition, and productivity of plasma-producing horses used for snake antivenom manufacture: A comparison of two industrial bleeding methods

The immunization and industrial bleeding of horses are essential stages for producing snake antivenoms. In Costa Rica, the traditional method involves stimulating the antibody response of horses by periodically injecting venoms, collecting hyperimmune plasma over three consecutive bleeding days, and repeating this process every eight weeks. While this method does not cause major physical or hematological issues in horses, the associated stress has not been evaluated. We compared this traditional method with an alternative method that involves injecting venoms, collecting hyperimmune plasma in a single bleeding day, and repeating the process every two weeks. We assessed stress (via serum and fecal cortisol levels and an ethological study), hematological parameters (hematocrit and hemoglobin concentration), and plasma productivity over eight months. Serum cortisol levels remained within the normal range for both methods throughout the immunization/bleeding cycle. However, serum and fecal cortisol levels were significantly higher in horses subjected to the traditional method compared to those in the alternative method. Neither method caused significant hematological alterations. Notably, the alternative method yielded a higher volume of plasma. We concluded that adopting the alternative method ensures horse welfare while improving industrial bleeding productivity. This approach may reduce costs and improve the availability of this essential treatment for vulnerable populations.

Comparison of the intrageneric neutralization scope of monospecific, bispecific/monogeneric and polyspecific/monogeneric antisera raised in horses immunized with sub-Saharan African snake venoms

BACKGROUND

Snakebite envenomation inflicts a high burden of mortality and morbidity in sub-Saharan Africa. Antivenoms are the mainstay in the therapy of envenomation, and there is an urgent need to develop antivenoms of broad neutralizing efficacy for this region. The venoms used as immunogens to manufacture snake antivenoms are normally selected considering their medical importance and availability. Additionally, their ability to induce antibody responses with high neutralizing capability should be considered, an issue that involves the immunization scheme and the animal species being immunized.

METHODOLOGY/PRINCIPAL FINDINGS

Using the lethality neutralization assay in mice, we compared the intrageneric neutralization scope of antisera generated by immunization of horses with monospecific, bispecific/monogeneric, and polyspecific/monogeneric immunogens formulated with venoms of Bitis spp., Echis spp., Dendroaspis spp., spitting Naja spp. or non-spitting Naja spp. It was found that the antisera raised by all the immunogens were able to neutralize the homologous venoms and, with a single exception, the heterologous congeneric venoms (considering spitting and non-spitting Naja separately). In general, the polyspecific antisera of Bitis spp, Echis spp, and Dendroaspis spp gave the best neutralization profile against venoms of these genera. For spitting Naja venoms, there were no significant differences in the neutralizing ability between monospecific, bispecific and polyspecific antisera. A similar result was obtained in the case of non-spitting Naja venoms, except that polyspecific antiserum was more effective against the venoms of N. melanoleuca and N. nivea as compared to the monospecific antiserum.

CONCLUSIONS/SIGNIFICANCE

The use of polyspecific immunogens is the best alternative to produce monogeneric antivenoms with wide neutralizing coverage against venoms of sub-Saharan African snakes of the Bitis, Echis, Naja (non-spitting) and Dendroaspis genera. On the other hand, a monospecific immunogen composed of venom of Naja nigricollis is suitable to produce a monogeneric antivenom with wide neutralizing coverage against venoms of spitting Naja spp. These findings can be used in the design of antivenoms of wide neutralizing scope for sub-Saharan Africa.

Machine-learning guided Venom Induced Dermonecrosis Analysis tooL: VIDAL

Snakebite envenoming is a global public health issue that causes significant morbidity and mortality, particularly in low-income regions of the world. The clinical manifestations of envenomings vary depending on the snake's venom, with paralysis, haemorrhage, and necrosis being the most common and medically relevant effects. To assess the efficacy of antivenoms against dermonecrosis, a preclinical testing approach involves in vivo mouse models that mimic local tissue effects of cytotoxic snakebites in humans. However, current methods for assessing necrosis severity are time-consuming and susceptible to human error. To address this, we present the Venom Induced Dermonecrosis Analysis tooL (VIDAL), a machine-learning-guided image-based solution that can automatically identify dermonecrotic lesions in mice, adjust for lighting biases, scale the image, extract lesion area and discolouration, and calculate the severity of dermonecrosis. We also introduce a new unit, the dermonecrotic unit (DnU), to better capture the complexity of dermonecrosis severity. Our tool is comparable to the performance of state-of-the-art histopathological analysis, making it an accessible, accurate, and reproducible method for assessing dermonecrosis in mice. Given the urgent need to address the neglected tropical disease that is snakebite, high-throughput technologies such as VIDAL are crucial in developing and validating new and existing therapeutics for this debilitating disease.

AHA: AI-guided tool for the quantification of venom-induced haemorrhage in mice

Venom-induced haemorrhage constitutes a severe pathology in snakebite envenomings, especially those inflicted by viperid species. To both explore venom activity accurately and evaluate the efficacy of viperid antivenoms for the neutralisation of haemorrhagic activity it is essential to have available a precise, quantitative tool for empirically determining venom-induced haemorrhage. Thus, we have built on our prior approach and developed a new AI-guided tool (AHA) for the quantification of venom-induced haemorrhage in mice. Using a smartphone, it takes less than a minute to take a photo, upload the image, and receive accurate information on the magnitude of a venom-induced haemorrhagic lesion in mice. This substantially decreases analysis time, reduces human error, and does not require expert haemorrhage analysis skills. Furthermore, its open access web-based graphical user interface makes it easy to use and implement in laboratories across the globe. Together, this will reduce the resources required to preclinically assess and control the quality of antivenoms, whilst also expediting the profiling of haemorrhagic activity in venoms for the wider toxinology community.

Epidemiology of Snake Bites Linked with the Antivenoms Production in Colombia 2008-2020: Produced Vials Do Not Meet the Needs

Introduction

Snakebite envenomation is a public health event of mandatory reporting in Colombia. It is considered a medical emergency in which the government must guarantee antivenom availability. We describe snakebite epidemiological figures in Colombia between 2008 and 2020 and correlate them with antivenom manufacturing figures to determine rate coverage and the need for antivenom.

Methods

We performed an ecological study based on secondary official figures from the National Health Institute, the National Institute for Surveillance of Medicines and Foods, the National Administrative Department of Statistics and the Ministry of Health and Social Protection. Absolute and relative frequencies were calculated with 95% confidence intervals, position measurements, dispersion and central tendency.

Results

Through our research, we revealed that in the last 13 years (2008-2020), there were an average of 4467 annual snakebite envenomation cases affecting all the departments in Colombia. Antioquia reported the highest number of snakebites with 647 (95% CI 588-706) cases per year. The population incidence per 100,000 inhabitants was 9.5; the highest rates were found in Vaupés at 116.1 and Guaviare at 79.24. During the last seven years (2014-2020) Colombia produced an average of 21,104 antivenom vials per year, while the annual demand for antivenom is estimated at 54,440 units needed to guarantee access.

Discussion

Colombia does not produce sufficient vials to cover their needs, and this is why only 74.4% of accidents (out of the 92% not classified as dry bites) were treated, and even 9.7% of the severe accidents did not receive the specific treatment (8% of the victims were classified as dry bites). Figures support the regular antivenom shortages declared by the Ministry of Health and Social Protection in the last 13 years (11 health emergency declarations). New efforts are needed to: 1) boost the production of GMP-based high-quality antivenom, that covers the national needs and is made availability, 2) a better estimation method to calculate the need for antivenom in Colombia, and 3) implementation of production-distribution chains guaranteeing access in remote communities.

Assessing a 6-h endpoint observation time in the lethality neutralization assay used to evaluate the preclinical efficacy of snake antivenoms

The lethality neutralization assay in mice is the gold standard for the evaluation of the preclinical efficacy and specification fulfillment of snake antivenoms. However, owing to the animal suffering involved, this assay is a candidate to be replaced by in vitro alternatives or, at least, improved by the reduction of the number of animals used per experiment, the introduction of analgesia, and the refinement of the test. Since these tests are usually run for 24 or 48 h, one possibility to refine it is to shorten the endpoint observation time of the assay and so limiting the duration of suffering. To assess the effect of this modification of the standard procedure on the analytical properties of the assay, we compared the median lethal dose (LD50) and median effective dose (ED50) values, estimated through observation times of 6, 24 and 48 h. We used African and Latin American snake venoms and several batches of two polyspecific antivenoms. A significant correlation was found between LD50 and ED50 values estimated at the three observation times. Although some LD50 and ED50 values were significantly different at these time points, results of 6 h were robust enough to be used in the characterization of new antivenoms, the verification of specification compliance, and the parallel comparison of formulations. Our observations support the modification of the standard procedures used for assessing neutralizing ability of antivenoms by carrying out the observations at 6 h instead of 24 or 48 h, with the consequent reduction in the suffering inflicted upon mice during these assays. However, the shortening of the observation time in the lethality tests must be validated for each venom and antivenom before its introduction in the routine procedures.