A. Robbe-Vincent

Epidemiological data, clinical admission gradation and biological quantification by ELISA of scorpion envenomations in Algeria: effect of immunotherapy

An epidemiological and biological survey of scorpion envenomation was conducted in Algeria. Analysis of 182 medical files showed that 70% of the patients were stung by Androctonus australis. Most accidents occurred during the morning (40%) or the evening (30%). Two-thirds of the patients reached a hospital 1 hour after being stung. Their clinical symptoms classified 78% of them as Grade I (mild envenomation) and 17% of them as Grade II (moderate envenomation) on admission to hospital. No severe envenomation (Grade III) was reported. Most patients were treated with antivenom by the intramuscular route. Blood samples were collected before and after antivenom immunotherapy. A good correlation was observed between the grade of envenomation on admission and the blood venom concentrations measured by ELISA. The venom concentration decreased as function of the interval between the sting and blood collection (t1/2 = 2 h). Intramuscular injection of 10 ml of antivenom did not efficiently neutralize scorpion venom. Inflammation was followed by measuring IL6 concentration. IL6 peaked 1 h after scorpion envenomation. This study shows that optimization of the administration of antivenom is required to achieve clinical efficiency. In particular, intravenous injection of a larger dose of a more potent antivenom should be considered.

Viper bites in France: clinical and biological evaluation; kinetics of envenomations

1 A second inquiry was conducted in France to collect more accurate epidemiological, clinical and biological data from patients hospitalized after a viper bite, as well as treatment that they received. Fifty-seven well documented cases were classified in four grades of increasing severity defined according to the clinical signs of envenomation. 2 Local and systemic signs of envenomation appeared during the first 3 h, but the severity of the envenomation was observed to increase during the 12-24 h following bites in 50% of moderate and severe cases. One fatal case was reported. Biological analysis revealed an hyperleukocytosis in patients with moderate and severe envenomations. 3 The average length of hospitalization was of 1.7 ± 1.3 days for patients without signs of envenomation (grade 0) or presenting a minimal envenomation (grade 1), and statistically longer, 6.2 ± 2.9 days, for patients presenting moderate (grade 2) or severe envenomation (grade 3). 4 Levels of venom antigens in serum samples regularly collected during hospitalization were determined by a sandwich ELISA test. The serum venom levels determined during the first 4 h following the bite correlated with the severity of the envenomation when the symptoms were determined at their worst, usually 12-24 h later. In fact, concentrations higher than 20 ng ml-1 predict a moderate or severe clinical evolution. 5 The pharmacokinetics of venom antigens was also investigated during human envenomations. Venom antigens could be detected in the serum of patients as soon as half an hour after the bite, then decreased exponentially during the following hours with an apparent half-life of 8 h, similar in grade 2 and grade 3 patients, indicating that the kinetics of venom antigens in blood is independent of the severity of the envenomation.

Unusual neurotoxic envenomations by Vipera aspis aspis snakes in France

Vipera aspis aspis (V.a.a.) is the most dangerous poisonous snake in South-Eastern France. The clinical symptoms observed after V.a.a. envenomations involve mostly local signs (pain, edema) associated in the more severe cases with systemic symptoms (gastro-intestinal and cardiovascular manifestations). Since 1992, several unusual cases of moderate and severe `neurotoxic’ envenomations by V.a.a. snakes have been reported in a very localized area in South-Eastern France. Most of the human patients mainly suffered neurological signs owing to cephalic muscle paralysis. Drowsiness and dyspnea were observed for the most severe cases. Envenomed animals suffered respiratory distress and paralysis. The local signs were never as severe as observed after envenomations by vipers in other French regions. Human patients with moderate or severe clinical features received two intravenous injections of Viperfav2 antivenom, the first dose inducing the decrease of the neurological signs and the second reducing significantly the edema. Neurotoxic components immunologically cross-reacting with toxins from V. ammodytes ammodytes venom from Eastern Europe were detected in the blood of all patients suffering neurological symptoms after a V.a.a. bite. The protective efficacy of various antivenoms was evaluated in mice. The existence of geographical variations in the composition of V.a.a. venom emphasizes on the use of polyvalent antivenom in the treatment of viper envenomations in France. Human & Experimental Toxicology (2002) 21, 137 – 145.

Visualizing Non Infectious and Infectious Anopheles gambiae Blood Feedings in Naive and Saliva-Immunized Mice

Background Anopheles gambiae is a major vector of malaria and lymphatic filariasis. The arthropod-host interactions occurring at the skin interface are complex and dynamic. We used a global approach to describe the interaction between the mosquito (infected or uninfected) and the skin of mammals during blood feeding. Methods Intravital video microscopy was used to characterize several features during blood feeding. The deposition and movement of Plasmodium berghei sporozoites in the dermis were also observed. We also used histological techniques to analyze the impact of infected and uninfected feedings on the skin cell response in naive mice. Results The mouthparts were highly mobile within the skin during the probing phase. Probing time increased with mosquito age, with possible effects on pathogen transmission. Repletion was achieved by capillary feeding. The presence of sporozoites in the salivary glands modified the behavior of the mosquitoes, with infected females tending to probe more than uninfected females (86% versus 44%). A white area around the tip of the proboscis was observed when the mosquitoes fed on blood from the vessels of mice immunized with saliva. Mosquito feedings elicited an acute inflammatory response in naive mice that peaked three hours after the bite. Polynuclear and mast cells were associated with saliva deposits. We describe the first visualization of saliva in the skin by immunohistochemistry (IHC) with antibodies directed against saliva. Both saliva deposits and sporozoites were detected in the skin for up to 18 h after the bite. Conclusion This study, in which we visualized the probing and engorgement phases of Anopheles gambiae blood meals, provides precise information about the behavior of the insect as a function of its infection status and the presence or absence of anti-saliva antibodies. It also provides insight into the possible consequences of the inflammatory reaction for blood feeding and pathogen transmission.

Toxicity evolution of Vipera aspis aspis venom: identification and molecular modeling of a novel phospholipase A2 heterodimer neurotoxin1

We report the simultaneous presence of two phospholipase A2 (PLA2) neurotoxins in the venom of Vipera aspis aspis, the first such observation. One is monomeric and identical to ammodytoxin B of Vipera ammodytes ammodytes. Its presence may result from gene flux after interbreeding between V. aspis aspis and V. ammodytes ammodytes. The second, a novel heterodimer named vaspin, is very similar to vipoxin of Vipera ammodytes meridionalis and to PLA2‐I of Vipera aspis zinnikeri. It may result from expression of preexisting genes, the acidic subunit evolving from an ancestor common to ammodytin I2 from V. ammodytes ammodytes, which we also found in V. aspis aspis.

Different Evolution of Phospholipase A2 Neurotoxins (β-Neurotoxins) from Elapidae and Viperidae Snakes

Snake venoms are complex mixtures of proteins including enzymes, biologically active compounds, and toxins. Among snake venom toxins, neurotoxins that block the neuromuscular transmission of skeletal muscles play a major role in the lethal action of the venom of humerous snakes. They act either at the postsynaptic level (a-neurotoxins) by preventing the binding of acetylcholine on its receptor’ or at the presynaptic level by affecting neurotransmitter release. Two kinds of presynaptic neurotoxins have been recognized: the facilitatory neurotoxins, which are devoid of enzymatic activity and either block a voltage-sensitive K+ channel (Le., dendrotoxins*) or inhibit acetylcholinesterase (i.e., fasciculins’), and the p-neurotoxins, which are characterized by a phospholipase Al activity. Phospholipases A2 (phosphatide acylhydrolase, EC 3.1.1.4) are enzymes that catalyze the hydrolysis of the 2-acylester bond in 3-sn-phosphoglycerides. Extracellular forms of phospholipases A2 are extremely abundant in the secretions from exocrine glands, such as pancreas, and venomous glands from snakes, bees, scorpions, etc., as well as at inflammatory sites. They are homologous polypeptides of 13-14 kDa that have been subdivided into three classes, according to the similarities of their polypeptide sequence^.^ Class I includes phospholipases A2 from mammalian pancreas and from Elapidae and Hydrophiidae venoms. Class I1 comprises the phospholipases A2 from Viperidae (Viperinae and Crotalinae) venoms, as well as mammalian phospholipases A2 from inflammatory sites or secreted by blood platelets. Class 111 includes phospholipases A2 from Apis mellifera and Heloderma venoms.