Immunization against snake venoms

Oliveira I, Rimbault C, A. Cerni F, Wen FH, Sachett J, Sartim MA, Laustsen AH, Monteiro WM. Current Knowledge on Snake Dry Bites

Snake 'dry bites' are characterized by the absence of venom being injected into the victim during a snakebite incident. The dry bite mechanism and diagnosis are quite complex, and the lack of envenoming symptoms in these cases may be misinterpreted as a miraculous treatment or as proof that the bite from the perpetrating snake species is rather harmless. The circumstances of dry bites and their clinical diagnosis are not well-explored in the literature, which may lead to ambiguity amongst treating personnel about whether antivenom is indicated or not. Here, the epidemiology and recorded history of dry bites are reviewed, and the clinical knowledge on the dry bite phenomenon is presented and discussed. Finally, this review proposes a diagnostic and therapeutic protocol to assist medical care after snake dry bites, aiming to improve patient outcomes.

Comparison of the biodistribution of free or liposome-entrapped Crotalus durissus terrificus (South American rattlesnake) venom in mice

The local absorption rate, clearance and tissue distribution of Crotalus durissus terrificus venom, (Cdt) were examined using a two-antibody sandwich ELISA assay. We compared the biodistribution of both free or encapsulated Cdt in mice. Following subcutaneous injection of 10 microg/mouse of free Cdt (0.8 LD50), venom was detected in serum after 15 min, showed its highest level at 30 min (45+/-5 ng/ml) and was cleared from the circulation after 6 h. After 2 h of inoculation, venom was detected in the kidney (57+/-9 ng/g of tissue), spleen (18+/-4 ng/g of tissue) and brain (14+/-6 ng/g of tissue). For both subcutaneous or intravenous injection of free Cdt, venom was firstly detected in the kidney. No Cdt appeared either in the kidney, spleen, brain, or other tissues after subcutaneous inoculation of encapsulated venom even though a higher dose was used, 25 microg/mouse (2 LD50). Venom remained at the site of injection for a period of 1 week. Following intravenous injection of encapsulated venom (5 microg/mouse, 2 LD50), venom was detected in liver and spleen tissues. The biodistribution of encapsulated venom is discussed in relation to the effects of reduction of toxicity and increase of adjuvanticity.

Immunization with liposome-encapsulated Bothrops jararaca venom

The venom of Bothrops jararaca (BjV) snake was encapsulated into liposomes. The toxicity and ability of the resultant liposomes to protect mice were evaluated. No acute toxicity was found in mice, when liposomes were subcutaneously injected whereas the same dose of venom emulsified in Freund's adjuvant caused the mice to die. Immunization with the venom containing liposomes and associated immunostimulants, protected 50% of mice after challenge with BjV (4 x LD50). The hemorrhagic activity induced by BjV was reduced after immunization with liposomes associated with immunostimulants, similarly to immunization with BjV emulsified in Freund's adjuvant. However, mice immunized with BjV:Freund's were better protected against the lethal effects of the venom.

Encapsulation of native crotoxin in liposomes: a safe approach for the production of antivenom and vaccination against Crotalus durissus terrificus venom

Crotoxin, the neurotoxic component of Crotalus durissus terrificus (Cdt) venom that displays phospholipase A2 activity, was successfully encapsulated into dehydration-rehydration vesicles (DRV/crotoxin) and reverse-phase evaporation vesicles (REV/crotoxin) made from sphingomyelin and cholesterol. The encapsulation efficiency of native crotoxin was higher in DRV/crotoxin than in REV/crotoxin. DRV/crotoxin was not toxic when i.v. inoculated in mice at a dose of crotoxin as high as 91 times its L.D50 or when s.c. inoculated at 42 times its LD50. On the other hand, crotoxin released from DRV/crotoxin retained its original toxicity. REV/crotoxin was found to be at least 1.9 times more toxic than DRV/crotoxin. The fact that DRV/crotoxin retained crotoxin more efficiently than REV/crotoxin may account for the difference in acute toxicity between the two preparations. DRV/crotoxin, when s.c. inoculated in mice, induced anti-crotoxin antibodies that protected animals against the lethal effect of Cdt venom. Following immunization with three doses of DRV/crotoxin (3 x 20 micrograms of crotoxin/mouse) and challenge with 8 x LD50 of Cdt venom, 75% of mice were protected. The DRV/crotoxin preparation was compared to crotoxin emulsified in Freund's adjuvant (FCA/crotoxin). DRV/crotoxin was found to be less toxic than FCA/crotoxin, and to induce lower levels of anti-crotoxin antibodies but similar levels of protection when inoculated at high doses (20 or 70 micrograms crotoxin/mouse). When DRV/crotoxin was adsorbed to alum at the time of immunization, it induced antibody and protection levels comparable to those produced by FCA/crotoxin.

Immunization against Echis ocellatus (carpet viper) venom using liposomes incorporating immunostimulants: role of lipopolysaccharide in conferring protection in a mouse model

Varying doses of whole West African Echis ocellatus venom were incorporated, with or without immunostimulants, into membrane-stabilized reverse phase evaporation (REV) liposomes. Preparations were given either subcutaneously (s.c.) or intravenously (i.v.) to mice and the immune responses compared. Addition of lipopolysaccharide (LPS) significantly increased the venom antibody response. Lipid A produced a less pronounced and less sustained effect and the addition of muramyl dipeptide analogues made no significant contribution to the antibody response. The protective ability of circulating venom antibodies was assessed by challenging the immunized mice with a minimum lethal dose of whole venom after 175 days. A dose of 250 micrograms E. ocellatus venom + 300 micrograms LPS in REVs injected s.c. conferred the highest protection against lethal venom effects. Orally administered venom/liposomes incorporated with the mucosal adjuvant avridine primed the antibody response and produced a classic secondary response following a sublethal boost of whole venom. Single injections of venom or venom fraction/liposome preparations which produce a high and sustained immune response have potential in commercial antivenom production and in active immunization of man in areas of high snakebite incidence and mortality.

Snake venoms in science and clinical medicine. 2. Applied immunology in snake venom research

Enzyme-linked immunosorbent assay (ELISA) is a very important tool for studying both the epidemiology and clinical effects of snake bite in man. For epidemiology ELISA depends on the development and persistence of specific humoral venom antibody in previous snake bite victims. In the Nigerian savanna 63% of previous bite victims possessed specific venom antibodies against Echis carinatus venom; in Ecuador, where there is a 5% annual mortality due to snake bite in a population of Waorani Indians, venom antibodies against a wide range of different venoms were identified in previous bite victims using ELISA. In certain areas it is often not possible, using the symptoms of envenoming, to determine which species of snake has bitten the patient. Field studies using ELISA in Nigeria and Thailand have been successful in establishing the species responsible for envenoming. Current studies are in progress on the development of a rapid immunoassay which should be capable of detecting the biting species within 5-10 min of sampling from the admission patient. This will be useful for the clinician as it will enable the rapid detection of the species responsible for envenoming and, therefore, the use of the correct antivenom. Experimental work on the development of new methods of antivenom production includes immunization of experimental animals with venom/liposome preparations, the preparation of venom antigens using monoclonal antibodies on affinity columns, and recombinant deoxyribonucleic acid technology. Liposomal immunization requires only a single injection of venom to obtain a rapid, high level and protective immune response. Venom liposomes may also be given orally resulting in a serum immunoglobulin G immune response in experimental animals. Use of such a system may eventually result in immunization of man in areas of high snake bite incidence and mortality.

Use of liposomes for protective immunisation against Crotalus durissus (tropical rattlesnake) venom

Crotalus durissus venom has been described as a weak antigen when injected in combination with Freund's complete adjuvant during the course of traditional methods of equine immunisation. Antibody production is slow and unpredictable, with a wide variation in individual responses. In this experimental study, C. durissus venom was incorporated into stabilised sphingomyelin-cholesterol liposomes both in the presence and absence of lipopolysaccharide immunostimulant and injected by both i.v. and s.c. routes into mice and rabbits. A rapid, sustained and protective immune response was obtained following a single injection of these preparations in mice. Antibody levels were estimated using enzyme-linked immunosorbent assay (ELISA), and the protective effect was evaluated by subsequent challenge with a subcutaneous minimum lethal dose of the venom. Results indicated that the immune response was significantly potentiated by the presence of immunostimulant in the venom liposomes. The use of C. durissus venom liposomes should be a useful tool for the immunisation of animals both in experimental and commercial procedures.

Characterisation of a monoclonal antibody capable of neutralising the haemorrhagic activity of West African Echis carinatus (carpet viper) venom

A murine monoclonal antibody (SV-1/F10) was highly specific immunologically for West African E.carinatus venom both by ELISA and immunoblotting. In cross-protection tests in vivo, it possessed strong antihaemorrhagic activity. This IgGl monoclonal antibody recognised an epitope present in a protein band of 124,000 mol. wt using immunoblotting of non-reduced Nigerian and Ghanaian E.carinatus venoms, as well as in a second protein band of 105,000 mol. wt in Ghanaian E.carinatus venom. The SV-1/F10 monoclonal antibody is of potential use for the isolation of West African E.carinatus venom haemorrhagin from whole venom, allowing the possibility of elucidation of the mechanism of its actions as well as its interactions with antibody.

Trial of Russell's Viper Venoid. II. Human immunization with venoid. Burma, DMR Working Group on Clinical Trial of Russell's Viper Venoid

A previously developed, refined Russell's viper venoid was given to human volunteers to find out if a protective immune response is obtainable and to observe for adverse effects. 12 subjects were immunized by subcutaneous injection of 0.5 ml of venoid followed by two booster injections at four-week intervals and six subjects served as control. Both local and systemic reactions were mild. No abnormality was detected in the laboratory tests performed. Significant rise of antibody titre was detected in all immunized subjects which persisted for 24 weeks. The antibody level achieved in human subjects is equivalent to levels seen in immunized monkeys which withstood doses of venom which would otherwise have been lethal.

Use of liposomes for protective immunisation in sheep against Echis carinatus snake venom

Nigerian Echis carinatus venom incorporated into sphingomyelin-cholesterol liposomes stabilized with osmium tetroxide produced a rapid, sustained and protective immune response when injected i.v. into sheep. The response was similar to that reported earlier in mice. The implications of the findings are discussed in relation to the production of cheaper and more effective antivenoms. The possible use of immunostimulants for increasing the protective effect of antisera raised using this method are also considered.