Immune Maturation Effects on Viral Neutralization and Avidity of Hyperimmunized Equine Anti-SARS-CoV-2 Sera.

Mass-vaccination against COVID-19 is still a distant goal for most low-to-middle income countries. The experience gained through decades producing polyclonal immunotherapeutics (such as antivenoms) in many of those countries is being redirected to develop similar products able to neutralize SARS-CoV-2 infection. In this study we analyzed the biological activity (viral neutralization or NtAb) and immunochemical properties of hyperimmune horses' sera (HHS) obtained during initial immunization (I) and posterior re-immunization (R) cycles using the RBD domain of the SARS-CoV-2 spike protein as antigen. HHS at the end of the R cycle showed higher NtAb titers when compared to those after the I cycle (35,585 vs. 7000 mean NtAb, respectively). Moreover, this increase paralleled an increase in avidity (95.2% to 65.2% mean avidity units, respectively). The results presented herein are relevant for manufacturers of these therapeutic tools against COVID-19.

Cross-reactivity of some Micrurus venoms against experimental and therapeutic anti-Micrurus antivenoms.

We developed experimental equine polyvalent and monovalent antivenoms against the venoms of Micrurus (M.) fulvius, M. nigrocinctus and M. surinamensis and studied their immunochemical reactivity on the venoms used as immunogens and on M. pyrrhocryptus, M altirostris and M. balyocoriphus venoms. Assessment of the neutralizing capacity of the polyvalent experimental antivenom was based on inhibition of lethality (preincubation and rescue assay experiments in mice) and indirect hemolytic and phospholipase activities. The immunochemical reactivity and neutralizing capacity were compared with those of two therapeutic antivenoms used for the treatment of coral snake envenomation in North America and in Argentina. In general, the experimental antivenom conferred a comparable level of neutralization against the venoms used as immunogens when compared to the therapeutic antivenoms and a certain level of cross-neutralization against the other venoms. The results suggest the need for additional venoms in the immunogenic mixture used, in order to obtain a broad spectrum anti-Micrurus antivenom with a good neutralizing potency. Paraspecific neutralization of South American coral snake venoms, although present at a higher level than the neutralization conferred by available nonspecific Micrurus therapeutic antivenoms, was rather low in relation to the specific neutralizing capacity.

Biotechnological potential of Phospholipase D for Loxosceles antivenom development.

Loxoscelism is one of the most important forms of araneism in South America. The Health Authorities from countries with the highest incidence and longer history in registering loxoscelism cases indicate that specific antivenom should be administered during the first hours after the accident, especially in the presence or at risk of the most severe clinical outcome. Current antivenoms are based on immunoglobulins or their fragments, obtained from plasma of hyperimmunized horses. Antivenom has been produced using the same traditional techniques for more than 120 years. Although the whole composition of the spider venom remains unknown, the discovery and biotechnological production of the phospholipase D enzymes represented a milestone for the knowledge of the physiopathology of envenomation and for the introduction of new innovative tools in antivenom production. The fact that this protein is a principal toxin of the venom opens the possibility of replacing the use of whole venom as an immunogen, an attractive alternative considering the laborious techniques and low yields associated with venom extraction. This challenge warrants technological innovation to facilitate production and obtain more effective antidotes. In this review, we compile the reported studies, examining the advances in the expression and application of phospholipase D as a new immunogen and how the new biotechnological tools have introduced some degree of innovation in this field.

Study on the obtaining of Tityus trivittatus venom in Argentina.

Envenomation by scorpions of the genus Tityus is an important public health problem in Argentina, involving near 8000 stings and 2 deaths each year. Treatment for envenomation is the use of specific antivenom and intensive hospital care. Antivenom is produced by the Ministry of Health and freely distributed throughout the country. For antivenom production it is necessary to collect scorpion venom, which is a difficult task because although scorpions can be found in Argentina, they are less abundant than in warmer latitudes. For this reason venom collection constitutes a bottleneck for antivenom production. Although in Argentina several species of Tityus can be found, most of the accidents are caused by Tityus trivittatus, and the venom of this scorpion has historically been the venom used for antivenom production. We analyzed retrospectively 26 pools of telson homogenates (6964 telsons) and 37 pools of milked venom obtained by electrical stimulation (equivalent to 6841 milkings). Lethal potencies of samples from different provinces were very similar, although venom from scorpions of Buenos Aires city showed the lowest potency. The venom obtained by milking (median LD50 12.3 µg), provided batches containing LD50s more potent when compared with the venom obtained from telson homogenates (p < 0.0001). Many batches of telson homogenates (30%) showed lower potencies than acceptable for antivenom production and control. In addition to the study of the venom yield, the records of immunization of horses, the potency of the batches and the protein content of each batch of anti-scorpion antivenom produced were analyzed, comparing those produced using milked venom with those using telson homogenates as immunogens. Batches produced using milked venom required a shorter period of immunization (p < 0.0001), rendered higher neutralizing titers (p 0.0350) and possessed lower protein content (p 0.0092). Results clearly showed that the milking of scorpions is a more efficient tool to obtain venom for antivenom production in comparison to the use of telson homogenates.

Lesiones por Raya de Río: Acerca de tres casos en el Río de la Plata, Argentina / Injuries caused by River Stingrays:About three cases in the Río de la Plata ("River Plate") river, Argentina

Resumen Las rayas del género Potamotrygon son peces con forma dorsoventral aplanada. Son animales tranquilos, que solo atacan al ser agredidos o amenazados. Poseen en su cola estructuras punzantes, conocidas como espinas, envueltas por una vaina tegumentaria con tejidos secretores de componentes tóxicos. Suelen permanecer quietos en aguas superficiales, ocultos bajo arena o barro, lo que facilita su contacto accidental con humanos, con la probable generación de lesiones, al utilizar su cola hacia arriba y adelante en forma de látigo. Las lesiones son más frecuentes en hombres, en los meses estivales y en los miembros inferiores, seguidos por los miembros superiores. La lesión se asocia a dolor urente, casi inmediato y de gran intensidad, por el efecto traumático generado por las espinas, la persistencia de las mismas o sus fragmentos y por el efecto químico generado por sus toxinas. En ocasiones se asocia a la formación de necrosis y úlceras profundas o reacción granulomatosa por cuerpo extraño, con requerimientos de desbridamiento quirúrgico. Las lesiones fatales son infrecuentes y pueden resultar de una lesión torácica penetrante, laceraciones cervicales, compromiso de vía aérea, heridas vasculares o infecciones. Se deben realizar estudios de imágenes para evidenciar restos de la espina. La herida debe ser higienizada y se debe retirar la espina o sus fragmentos a la brevedad y sumergir el área lesionada en agua tan caliente como el paciente pueda tolerar, por 30 a 90 minutos, buscando disminuir el dolor y generar vasodilatación, junto con la analgesia y cobertura antibiótica y antitetánica. Se presentan tres casos de pacientes con lesiones por raya de río, dos de ellos por Potamotrygon brachyura, especie endémica del río de La Plata y el tercero por una raya no identificada. Se expone además una revisión bibliográfica a fin de remarcar la importancia de su diagnóstico temprano y su correcto abordaje.

Abstract The rays of the Potamotrygon genus are fish with a dorsoventrally flattened shape. They are calm animals that only attack when are provoked or threatened. They have sharp structures in their tail, known as spines, wrapped by a tegumentary sheath with tissues that secrete toxic components. They typically remain still in shallow waters, concealed under sand or mud, which increases accidental human contact. This contact can lead to injuries, as they whip their tail upwards and forwards. Injuries are more common in males during summer months, often affecting lower limbs followed by upper limbs. Injuries are characterized by immediate intense burning pain due to trauma from the spine or its fragments and chemical effects from its toxins. Occasionally, injuries lead to necrosis, deep ulcers, or foreign body granulomatous reactions requiring surgical debridement. Fatal injuries are rare but can result from thoracic penetration, cervical lacerations, airway compromise, vascular wounds, or infections. Imaging studies are necessary to detect spine remnants. Wounds should be cleaned, and spines or fragments removed promptly. The affected area should be immersed in water, as hot as tolerable for 30 to 90 minutes to reduce pain, induce vasodilation, and must supplemented with analgesia, antibiotic coverage, and tetanus prophylaxis. Three cases of river stingray injuries are presented, two from Potamotrygon brachyura, an endemic species of the Rio de la Plata river, and one from an unidentified ray. Additionally, a literature review emphasizes the importance of early diagnosis and proper management.

New insights into the proteomic characterization of the coral snake Micrurus pyrrhocryptus venom.

A proteomic analysis of the soluble venom of the coral snake Micrurus pyrrhocryptus is reported in this work. The whole soluble venom was separated by RP-HPLC and the molecular weights of its components (over 100) were determined by mass spectrometry. Three main sets of components were identified, corresponding to peptides with molecular masses from 5 to 8 kDa, proteins from 12 to 16 kDa and proteins from 20 to 30 kDa. Two components were fully sequenced: one α-neurotoxic peptide of 7210 Da with slight blocking activity of the nicotinic acetylcholine receptor (nAChR) and a phospholipase A2 (PLA2) with molecular weight 13517 Da and no effect on the nAChR. PLA2 activity was evaluated for all RP-HPLC components. In addition, N-terminal sequence was obtained for eleven components using Edman degradation. Among these, three were similar to known PLA2's, six to three-finger toxins (3FTx) and one to Kunitz-type serine protease inhibitors. Two-dimensional gel electrophoresis of the venom allowed the separation of about thirty spots with components of molecular weights from 25 to 70 kDa. Seventeen spots were recovered from the gel, digested with trypsin and the corresponding peptides (85) were sequenced by MS/MS allowing identification of amino acid sequences with similarities to snake venom metalloproteases (SVMP), PLA2's, L-amino acid oxidases (LAAO), acetylcholinesterases (AChE) and serine proteases (SP). In addition, LC-MS analysis of peptides obtained from tryptic digestion of whole soluble venom allowed the identification of 695 peptides, whose amino acid sequence could correspond to at least 355 components found in other snake venoms, where C-type lectins, vespryns, zinc finger proteins, and waprins were found, among others. These results show the complexity of the venom and provide important knowledge for future work on identification and activity determination of venom components from this coral snake.

Toxicity of two North American Loxosceles (brown recluse spiders) venoms and their neutralization by antivenoms.

The toxic, biochemical, and immunological characteristics of L. boneti and L. reclusa venoms and its neutralization by anti-L. boneti and anti-L. reclusa antivenoms were studied. The electrophoretic profile showed very similar patterns and the toxic activities were very close. Immunological studies showed cross-reactivity among L. boneti and L. reclusa venoms, with L. boneti and L. reclusa experimental antivenoms, and anti-L. gaucho and anti-L. laeta antivenoms. The venom of L. laeta showed low immunological reactivity with the North American Loxosceles antivenoms. Experimental anti-North American Loxosceles antivenoms protected mice of the systemic toxicity and were able to prevent necrosis in rabbit skin after the injection of the venom. Both antivenoms displayed cross neutralization. The results showed that both Loxosceles venoms have very close toxic, biochemical, and immunological characteristics, and that either monospecific antivenoms or an antivenom raised with L. boneti and L. reclusa venoms as immunogens could be useful for treating bites by North American Loxosceles spiders.

Lethality and histopathological alterations caused by Phoneutria nigriventer spider venom from Argentina: Neutralization of lethality by experimental and therapeutic antivenoms.

Although the spiders of the genus Phoneutria cause envenomation and their presence has been described in several provinces of the north of Argentina, they are not as common as other spiders of sanitary importance. In the present work, we studied the toxicity of samples of venom of Phoneutria spiders from the provinces of Misiones (where severe envenomation and deaths by Phoneutria have been recorded) and Jujuy (where no deaths have been recorded and severe envenomations are not frequent). To this end, we assessed the lethal potency in mice and guinea pigs and the histopathological alterations caused by both venoms, as well as the neutralization by the commonly used therapeutic antivenom produced by the Butantan Institute in Brazil and by an experimental antivenom developed with venom of P. nigriventer from Misiones. There were no differences in the lethality of the venoms of spiders from both regions. Post mortem examination showed that the heart and lungs were the most affected organs, while important pulmonary edema was seen macroscopically. Histological analysis showed edema, atelectasis, emphysema and cardiac lesion in both experimental models. The antivenoms assayed showed good neutralization of the venoms in the two experimental models. Despite the different geographic origins, the venoms showed similar toxicity and both the experimental antivenom and therapeutic antivenmos were able to neutralize the venoms of Argentinean P. nigriventer.

Cross neutralization of coral snake venoms by commercial Australian snake antivenoms.

CONTEXT: Although rare, coral snake envenomation is a serious health threat in Brazil, because of the highly neurotoxic venom and the scarcely available antivenom. The major bottleneck for antivenom production is the low availability of venom. Furthermore, the available serum is not effective against all coral snake species found in Brazil. An alternative to circumvent the lack of venom for serum production and the restricted protection of the actually available antivenom would be of great value. We compared the Brazilian coral snake and mono and polyvalent Australian antivenoms in terms of reactivity and protection. METHODS: The immunoreactivity of venoms from 9 coral snakes species were assayed by ELISA and western blot using the Brazilian Micrurus and the Australian pentavalent as well as monovalent anti-Notechis, Oxyuranus and Pseudechis antivenoms. Neutralization assays were performed in mice, using 3 LD50 of the venoms, incubated for 30 minutes with 100 µL of antivenom/animal. DISCUSSION: All the venoms reacted against the autologous and heterologous antivenoms. Nevertheless, the neutralization assays showed that the coral snake antivenom was only effective against M. corallinus, M. frontalis, M. fulvius, M. nigrocinctus and M. pyrrhocryptus venoms. On the other hand, the Australian pentavalent antivenom neutralized all venoms except the one from M. spixii. A combination of anti-Oxyuranus and Pseudechis monovalent sera, extended the protection to M. altirostris and, partially, to M. ibiboboca. By adding Notechis antivenom to this mixture, we obtained full protection against M. ibiboboca and partial neutralization against M. lemniscatus venoms. CONCLUSIONS: Our findings confirm the limited effectiveness of the Brazilian coral snake antivenom and indicate that antivenoms made from Australian snakes venoms are an effective alternative for coral snake bites in South America and also in the United States were coral snake antivenom production has been discontinued.

Antivenom against Crotalus durissus terrificus venom: Immunochemical reactivity and experimental neutralizing capacity.

The venom of Crotalus durissus terrificus produces a neurotoxic and myotoxic syndrome that can lead to the death. Specific antivenom is the only treatment to neutralize the toxicity of the venom and the precocity in applying the antivenom is crucial for the efficiency of the treatment. We studied the variation of the immunochemical reactivity and neutralizing capacity of the specific antivenom on this venom in pre-incubation and rescue experiments, at different times. ELISA titers increased with longer venom-antivenom incubation times (p < 0.05) nevertheless incubation times had no effect on the neutralizing capacity of the antivenom. The antivenom dose necessary to rescue mice injected with 1.5 MMD (minimal mortal dose) 30 min after venom inoculation was over ten folds the dose of antivenom theoretically required to neutralize the same dose of venom according values obtained from pre-incubation experiments. Results showed that the in vitro immunochemical reactivity is not directly related to the neutralizing capacity. These observations underline the need for a rapid antivenom administration. Although preincubation experiments in mice are a powerful tool for the validation of the potency of the antivenoms in the productive process, it is clear that the nominal neutralization of the antivenoms must not be considered as a "stoichiometric" value regarding the venom to be neutralized in case of natural envenomation and emphasize the need of realization of clinical trials in order to evaluate the adequate doses of antivenom to be therapeutically used.

Toxicity of the venom of Latrodectus (Araneae: Theridiidae) spiders from different regions of Argentina and neutralization by therapeutic antivenoms.

"Black widow" spiders belong to the genus Latrodectus and are one of the few spiders in the world whose bite can cause severe envenomation in humans and domestic animals. In Argentina, these spiders are distributed throughout the country and are responsible for the highest number of bites by spiders of toxicological sanitary interest. Here, we studied the toxicity and some biochemical and immunochemical characteristics of eighteen venom samples from Latrodectus spiders from eight different provinces of Argentina, and the neutralization of some of these samples by two therapeutic antivenoms used in the country for the treatment of envenomation and by a anti-Latrodectus antivenom prepared against the venom of Latrodectus mactans from Mexico. We observed important toxicity in all the samples studied and a variation in the toxicity of samples, even in those from the same region and province and even in the same Latrodectus species from the same region. The therapeutic antivenoms efficiently neutralized all the venoms studied.

[Biological and immunological characteristics of the poison of Bothrops cotiara (Serpentes: Viperidae)]. / Características biológicas e inmunológicas del veneno de Bothrops cotiara (Serpentes: Viperidae).

Bothrops cotiara is a venomous snake sporadically found in the province of Misiones in Argentina, South of Brazil and Paraguay. Data on the clinics of the envenomation produced by its bite and on its venom are scarce. There is no information on the neutralizing capacity of the antivenoms available. In this study, the lethal potency, hemorrhagic, necrotizing, coagulant and thrombin-like, defibrinogenating, indirect hemolytic and fibrinolytic activities of the venom of B. cotiara specimens from the province of Misiones were determined. The toxic activities were within the range of those described for the other Bothrops species from Argentina, and the electrophoretic and chromatographic studies showed similarities with those described for the other bothropic venoms. The immunochemical reactivity of six South American anti Viper antivenoms (ELISA) have a strong reactivity with all the antivenoms studied. The neutralizing capacity of three of these therapeutic antivenoms against the lethal potency and hemorrhagic, necrotizing, coagulant, thrombin-like and hemolytic activities showed a very close neutralizing capacity. Our data strongly suggest that the antivenoms for therapeutic use available in this area of South America are useful to neutralize the toxic and enzymatic activities of the venom of this uncommon specie of Bothrops.

Venom yield and its relationship with body size and fang separation of pit vipers from Argentina.

The amount of venom that a snake can inject is related to its body size. The body size is related to head size and to the distance between fangs. To correlate snake body size, distance between fangs and distance between puncture wounds with the venom yield (and consequently with the venom dose potentially injected in a single snakebite), we studied these variables in two species of public health importance in South America, Bothrops (Rhinocerophis) alternatus, and Crotalus durissus terrificus. In all cases a positive correlation was observed between body length, fang separation distance, distance between puncture wounds and venom yield, with a regression coefficient over 0.5 for Bothrops alternatus and over 0.6 for Crotalus durissus terrificus in all cases, being the relation distance between punctures wounds and venom yield of 0.54 and 0.69 respectively. The difference between fang separation and puncture separation was never greater than 30%, with a mean difference around 13%. The strong relationships between body size, fang separation and venom yield may be useful for planning potential venom production in serpentariums. In addition, because puncture mark separation gives an approximate idea of the size of the snake, this provides a rough idea of the size of the snake that produced a bite and the potential amount of venom that could have been injected.

Hemorrhagic activity of Bothrops venoms determined by two different methods and relationship with proteolytic activity on gelatin and lethality.

The changes in hemorrhagic activity, proteolytic activity on gelatin and the lethal potency of four Bothrops venoms treated at different pH values or with EDTA were studied. Venoms from B. alternatus, B. jararaca, B. moojeni and B. neuwiedii of Argentina were preincubated at pH 5.8, 5.1 or 3.8 or with EDTA and the hemorrhagic activity expressed as size of the hemorrhagic lesion or as the amount of hemoglobin extracted, the proteolytic activity on gelatin and the lethal potency were determined. Although the MHDs recorded in rats were 19-56 fold higher than those recorded in mice, the A(550) extracted per gram of hemorrhagic haloes was very similar in rats or mice independent of the venom dose. Inhibition of proteolytic activity after preincubation at pH 5.1 or 3.8, agrees with the decreased amount of hemoglobin extracted from the hemorrhagic haloes, and with the increase in mean survival time after the i.p. injection to mice. Preincubation with EDTA resulted in 80% inhibition of hemorrhagic activity of B. jararaca venom and complete inhibition with the other Bothrops venoms tested. Measurement of the amount of hemoglobin extracted gives significant information in comparative studies, not available by measurement of the size of hemorrhagic haloes.

Comments on Environmental and Sanitary Aspects of the Scorpionism by Tityus trivittatus in Buenos Aires City, Argentina.

Deaths by venomous animals are medical emergencies that can lead to death and thus constitute sanitary problems in some regions of the world. In the South of America, the accidents by these animals are a common sanitary problem especially in warm, tropical or subtropical regions, related with rural work in several countries. Argentina is located in the extreme South of South America and a minor part of the continental surface is in tropical or subtropical regions, where most of the accidents by venomous animals happen. However, in the big cities in the center and South of the country, with no relation to rural work, scorpionism, mostly due to the synanthropic and facultative parthenogenetic scorpion Tityus trivittatus, has become a sanitary problem in the last few decades. This scorpion is present in the biggest cities of Argentina and in the last decades has killed over 20 children in provinces of the center and north of the country, mostly in big cities. In addition, it seems that this species is growing and spreading in new regions of the cities. In this revision, some characteristics of this scorpion regarding its habitat, spreading in Buenos Aires city, combat measures and available treatments are discussed.

Epidemiology of snakebite and use of antivenom in Argentina.

BACKGROUND: The incidence and case fatality rate of snakebite in Argentina are poorly known. METHODS: The authors used questionnaires provided with antivenoms by the primary manufacturer of anti-venoms in Argentina. RESULTS: A total of 8083 completed questionnaires was collected between 1978 and 1998. The annual incidence of snakebite was 1.8 bites per 100,000 inhabitants, with a high geographical heterogeneity; in the northern provinces of the country, the incidence can exceed 150 snakebites per 100,000 people per year. Bothrops (pit viper) bites predominated, accounting for 96.6% (6720/6957) of envenomations, bites from Crotalus (rattlesnake) accounted for 2.8% (195/6957), and bites from Micrurus (coral snake) for 0.6% (42/6957). Most patients were young men, who were generally bitten during agricultural activities, i.e. while working in the fields. Most snakebites (78.9%, 5852/7419) were to the lower limb, including 58.3% (4322/7419) to the foot. The case fatality rate was <0.04% (3/8083). Most envenomations (90%, 7275/8083) were treated with specific antivenom during the first 4 h after the bite. The median dose of antivenom was two vials for viper bites (Bothrops and Crotalus) and three vials for Micrurus bites. CONCLUSION: These preliminary results should enable manufacturers to increase the availability of appropriate antivenom and health authorities to improve the management of snakebites where they are most common.

Intraspecific differences in the immunochemical reactivity and neutralization of venom from Argentinean Bothrops (Rhinocerophis) alternatus by specific experimental antivenoms.

The venoms of Bothrops (Rhinocerophis) alternatus (B.a.) from different regions of Argentina have shown biochemical, toxicological and immunological variations. Considering these variations, we produced nine experimental antisera (rabbit, IgG) against venoms from snakes of nine different regions and a pool of venom, comprised of equal amounts of venoms from each region. The immunologic studies (ELISA, Westernblot) showed significant cross reactivity among all regional antivenoms with all regional venoms, with no significant differences regarding the specificity of the immunogens used for the production of antivenom. Neutralization of hemorrhage was variable (although all the antivenoms neutralized this activity in all venoms) and the neutralization of coagulant and phospholipase activities were evident in all cases. Some antivenoms neutralized toxic activities that were absent or very low in the venoms used as immunogen, on other non-homologous venoms (e.g. thrombin like activity). Despite the different toxic potencies of regional venoms, antivenoms developed using venoms of snakes from a particular region showed high immunochemical reactivity and cross-neutralizing capacity on snake venoms from different and distant regions, in occasions over those of the homologous antivenoms. These findings could be used to improve the generation of pools of venoms for the production of antivenoms.

Envenoming by coral snakes (Micrurus) in Argentina, during the period between 1979-2003.

Envenomation by coral snakes (Micrurus sp.) is one of the most dangerous injuries in America and it is considered as a serious medical emergency, however bites by these snakes appear to be rare. We analyzed epidemiological data, clinical signs and antivenom use in Argentina during the period between 1979-2003. During this period of study 46 non-fatal Micrurus bites were reported. The majority of cases were men from 31 to 40 years old. Bites occurred primarily in spring and summer. Most cases were reported from the northeast and northwest provinces of the country. The bites were mostly located on hands or feet and occurred mostly during agricultural activities and so mainly involved farmers. Only four cases occurred as a result of handling snakes. The median time it took for antivenom to be administrated was 60 minutes after the bite, and the median number of vials applied was 2. Local pain was mentioned and edema was reported in 41% of patients. All patients recovered without sequelae. This study showed a low incidence of Micrurus bites and low severity of envenomation. However, although no deaths have been reported during the last 30 years, given the toxicity of the venom of Micrurus snakes, the risk of severe envenomation should be considered.

Myotoxicity and nephrotoxicity by Micrurus venoms in experimental envenomation.

Micrurus venoms are essentially neurotoxic but other activities, such as myotoxicity, may be apparent under experimental conditions. Although this myotoxicity has been occasionally reported, there are no studies addressing it systematically across the genus, particularly in its relationship to other systemic manifestations such as renal impairment. The lethal potency of Micrurus fulvius, Micrurus nigrocinctus, Micrurus surinamensis, Micrurus altirostris, Micrurus balyocoriphus and Micrurus pyrrhocryptus venoms determined by us were in the range described for the genus and all venoms exhibited phospholipase activity, albeit at significantly different levels. Intramuscular venom injection caused variable local inflammation-edema; myotoxicity (as determined by plasma creatine kinase levels and histopathology) was apparent only in those venoms with highest phospholipase activity, namely M. fulvius, M. nigrocinctus and M. pyrrhocryptus. Kidneys of animals injected with these strongly myotoxic venoms showed lesions consisting in extensive tubular necrosis with nuclear fragmentation, destruction of the brush border, rupture of basal membrane and epithelial exfoliation of tubular cells, granular cast and thickening of tubules. The histological characteristics of the lesions suggest an important role for indirect glomerular damage by myoglobin deposits. Phospholipase and myotoxic activities did not correlate significantly to the lethal potency; renal lesions were, however, evident only in those venoms that caused extensive muscular damage. Although kidney lesions have not been described in clinical cases of Micrurus envenomation, the potential for nephrotoxicity of some of these venoms should be considered in the overall toxicological picture, at least in experimental conditions.