BackgroundAntivenom is the treatment of choice for snakebite, which annually kills an estimated 32,000 people in sub-Saharan Africa and leaves approximately 100,000 survivors with permanent physical disabilities that exert a considerable socioeconomic burden. Over the past two decades, the high costs of the most polyspecifically-effective antivenoms have sequentially reduced demand, commercial manufacturing incentives and production volumes that have combined to create a continent-wide vacuum of effective snakebite therapy. This was quickly filled with new, less expensive antivenoms, many of which are of untested efficacy. Some of these successfully marketed antivenoms for Africa are inappropriately manufactured with venoms from non-African snakes and are dangerously ineffective. The uncertain efficacy of available antivenoms exacerbates the complexity of designing intervention measures to reduce the burden of snakebite in sub-Saharan Africa. The objective of this study was to preclinically determine the ability of antivenoms available in Kenya to neutralise the lethal effects of venoms from the most medically important snakes in East Africa.MethodsWe collected venom samples from the most medically important snakes in East Africa and determined their toxicity in a mouse model. Using a ‘gold standard’ comparison protocol, we preclinically tested the comparative venom-neutralising efficacy of four antivenoms available in Kenya with two antivenoms of clinically-proven efficacy. To explain the variant efficacies of these antivenoms we tested the IgG-venom binding characteristics of each antivenom using in vitro IgG titre, avidity and venom-protein specificity assays. We also measured the IgG concentration of each antivenom.FindingsNone of the six antivenoms are preclinically effective, at the doses tested, against all of the most medically important snakes of the region. The very limited snake polyspecific efficacy of two locally available antivenoms is of concern. In vitro assays of the abilities of ‘test’ antivenom IgGs to bind venom proteins were not substantially different from that of the ‘gold standard’ antivenoms. The least effective antivenoms had the lowest IgG content/vial.ConclusionsManufacture-stated preclinical efficacy statements guide decision making by physicians and antivenom purchasers in sub-Saharan Africa. This is because of the lack of both clinical data on the efficacy of most of the many antivenoms used to treat patients and independent preclinical assessment. Our preclinical efficacy assessment of antivenoms available in Kenya identifies important limitations for two of the most commonly-used antivenoms, and that no antivenom is preclinically effective against all the regionally important snakes. The potential implication to snakebite treatment is of serious concern in Kenya and elsewhere in sub-Saharan Africa, and underscores the dilemma physicians face, the need for clinical data on antivenom efficacy and the medical and societal value of establishing independent preclinical antivenom-effica...
Transfection technology for malaria parasites provides a valuable tool for analyzing gene function and correlating genotype with phenotype. Transfection models are even more valuable when appropriate animal models are available in addition to complete in vitro systems to be able to fully analyze parasite-host interactions. Here we describe the development of such a model by using the nonhuman primate malaria Plasmodium knowlesi. Blood-stage parasites were adapted to long-term in vitro culture. In vitro-adapted parasites could readapt to in vivo growth and regain wild-type characteristics after a single passage through an intact rhesus monkey. P. knowlesi parasites, either in vitro adapted or in vivo derived, were successfully transfected to generate circumsporozoite protein (CSP) knockout parasites by double-crossover mechanisms. In vitro-transfected and cloned CSP knockout parasites were derived in a time span of only 18 days. Microscopic evaluation of developing oocysts from mosquitoes that had fed on CSP knockout parasites confirmed the impairment of sporozoite formation observed in P. berghei CSP knockout parasites. The P. knowlesi model currently is the only malaria system that combines rapid and precise double-crossover genetic manipulation procedures with complete in vitro as well as in vivo possibilities. This allows for full analysis of P. knowlesi genotype-phenotype relationships and host-parasite interactions in a system closely related to humans.The development of transfection technology for blood-stage malaria parasites (16, 23-25, 28, 29) is of great importance in the postgenomic era. It provides a direct way in which to correlate genotype with phenotype, and this enhances the further understanding of parasite biology. This will facilitate rational design of new vaccines and drugs, which are urgently needed to fight the malaria epidemic that kills annually between 1.5 and 2.7 million people, mainly young children, in Sub-Saharan Africa alone (7).Four species of Plasmodium are natural to humans (9), and two of them, Plasmodium falciparum and Plasmodium vivax, are the most prevalent and important in terms of disease. Phylogenetically, P. falciparum, the more deadly form of the two, forms a separate clade with Plasmodium reichenowi, which causes chimpanzee malaria, and P. vivax clusters with simian malarias (11). The nonhuman primate malaria, caused by Plasmodium knowlesi, a natural parasite of Macaca fascicularis, has a relatively broad host range extending to humans, where it causes a mild disease (8). The parasite is closely related to P. vivax (11), and many genes identified in P. vivax have homologues in P. knowlesi. To date, transfection techniques developed for malaria parasite blood stages (26) include episomal transfection and targeted integration with linear constructs for the rodent parasite Plasmodium berghei (24, 25), episomal transfection and targeted integration with circular DNA for the human parasite P. falciparum (28,29), and episomal transfection for the nonhuman primate malaria pa...
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