Snakebite epidemiology, outcomes and multi-cluster risk modelling in Eswatini

Halving snakebite morbidity and mortality by 2030 requires countries to develop both prevention and treatment strategies. The paucity of data on the global incidence and severity of snakebite envenoming causes challenges in prioritizing and mobilising resources for snakebite prevention and treatment. In line with the World Health Organisation's 2019 Snakebite Strategy, this study sought to investigate Eswatini's snakebite epidemiology and outcomes, and identify the socio-geographical factors associated with snakebite risk. Programmatic data from the Ministry of Health, Government of Eswatini 2019-2021, was used to assess the epidemiology and outcomes of snakebite in Eswatini. We developed a snake species richness map from the occurrence data of all venomous snakes of medical importance in Eswatini that was subjected to niche modelling. We formulated four risk indices using snake species richness, various geospatial datasets and reported snakebites. A multivariate cluster modelling approach using these indices was developed to estimate risk of snakebite and the outcomes of snakebite in Eswatini. An average of 466 snakebites was recorded annually in Eswatini. Bites were recorded across the entire country and peaked in the evening during summer months. Two cluster risk maps indicated areas of the country with a high probability of snakebite and a high probability of poor snakebite outcomes. The areas with the highest rate of snakebite risk were primarily in the rural and agricultural regions of the country. These models can be used to inform better snakebite prevention and treatment measures to enable Eswatini to meet the global goal of reducing snakebite morbidity and mortality by 50% by 2030. The supply chain challenges of antivenom affecting southern Africa and the high rates of snakebite identified in our study highlight the need for improved snakebite prevention and treatment tools that can be employed by health care workers stationed at rural, community clinics. [Abstract copyright: Copyright: © 2023 Padidar et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Two snakebite antivenoms have potential to reduce Eswatini’s dependency upon a single, increasingly unavailable product: Results of preclinical efficacy testing

Background Snakebite is a major public health concern in Eswatini, where treatment relies upon one antivenom—SAIMR Polyvalent. Although effective in treating snakebite, SAIMR Polyvalent is difficult to source outside its manufacturing country (South Africa) and is dauntingly expensive. We compared the preclinical venom-neutralising efficacy of two alternative antivenoms with that of SAIMR Polyvalent against the lethal and tissue-destructive effects of venoms from five species of medically important snakes using in vivo murine assays. The test antivenoms were ‘Panafrican’ manufactured by Instituto Clodomiro Picado and ‘PANAF’ manufactured by Premium Serums & Vaccines. Principal findings In vivo murine preclinical studies identified both test antivenoms were equally or more effective than SAIMR Polyvalent at neutralising lethal and tissue-destructive effects of Naja mossambica venom. Both test antivenoms were less effective than SAIMR Polyvalent at neutralising the lethal effects of Bitis arietans, Dendroaspis polylepis, Hemachatus haemachatus and Naja annulifera venoms, but similarly effective at neutralising tissue damage induced by B. arietans and H. haemachatus venoms. In vitro immunological assays identified that the titres and toxin-specificities of immunoglobulins (iGs) in the test antivenoms were comparable to that of SAIMR Polyvalent. Plasma clotting disturbances by H. haemachatus and N. mossambica were neutralised by the test antivenoms, whereas SAIMR Polyvalent failed to neutralise this bioactivity of N. mossambica venom. B. arietans SVMP activity was equally reduced by all three antivenoms, and H. haemachatus and N. mossambica PLA2 activities were neutralised by all three antivenoms. Conclusions While both Panafrican and PANAF antivenoms exhibited promising preclinical efficacies, both were less poly-specifically effective than SAIMR Polyvalent in these murine assays. The efficacy of these antivenoms against the lethal and tissue-destructive effects of N. mossambica venom, the most common biting species in Eswatini, identify that Panafrican and PANAF antivenoms offer effective alternatives to SAIMR Polyvalent for the treatment of snakebite in Eswatini, and potentially for neighbouring countries

PLA₂ assay optimisation data.

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Protein profiles of the venom protein components of five Eswatini snakes.

A: Venom proteins separated by SDS-PAGE under reducing conditions and stained with Coomassie blue to show all proteinaceous components. B: Immunoblot using normal horse IgG used as primary antibody negative control. C: Immunoblot using SAIMR Polyvalent as primary antibody. D: Immunoblot using Panafrican (ICP) antivenom as primary antibody. E: Immunoblot using PANAF (PS&V) antivenom as primary antibody.</p

ELISA endpoint raw data and ELISA avidity raw data.

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The preclinical venom-neutralising efficacy (antivenom ED₅₀) of the PANAF (PS&V) and Panafrican (ICP) antivenoms compared to SAIMR Polyvalent in the pre-incubation model of envenoming.

ED50 is defined as the volume of antivenom which protects 50% of mice from the lethal effects of venom. Each experiment used five mice per dose group. The assays utilised a venom challenge dose of 5 x venom LD50s (Table 2), except when it was necessary to reduce the challenge dose 3 x venom LD50s (indicated by red text). In these instances, the maximum volume limit of antivenom that can be injected intravenously was reached without reducing the venom lethality of the 5 x LD50 venom dose, therefore it was necessary to reduce the venom dose to determine an ED50 for the antivenom. Results are reported as ED50 determined by Probit analyses and expressed in (i) volume of antivenom and (ii) as μL of antivenom per mg of venom. 95% confidence intervals are reported in parentheses.</p

SVMP assay raw data.

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The titre of three antivenoms against five Eswatini venoms determined by end-point titration ELISA.

SAIMR Polyvalent (SAVP) shown in teal, Panafrican (ICP) shown in magenta, PANAF (PS&V) shown in blue, normal horse IgG shown in purple. Panel A: B. arietans. Panel B: D. polylepis. Panel C: H. haemachatus. Panel D: N. annulifera. Panel E: N. mossambica. Data points represent the mean of two replicates and error bars show the standard deviation. The vertical line at the 1:62,500 dilution represents the point at which Ig titres of each antivenom were compared.</p