Antivenom treatment in arachnidism

A comparison of serum antivenom concentrations after intravenous and intramuscular administration of redback (widow) spider antivenom

AIMS

There are no studies measuring antivenom concentrations following intramuscular administration. This study aimed to compare antivenom concentrations following intravenous and intramuscular administration of redback spider antivenom (RBSAV).

METHODS

Twenty patients recruited to a controlled trial comparing intramuscular and intravenous administration of antivenom had serial blood samples collected at 30 min intervals for 2 h after the administration of one or two doses of antivenom. Antivenom concentration was measured using an enzyme immunoassay.

RESULTS

Ten patients received intramuscular antivenom but antivenom could not be detected in serum after either one or two vials, at any time point. The median time of the final sample after commencement of antivenom treatment in these patients was 3.2 h (1.8-5 h). Ten patients received intravenous antivenom (three one vial and seven two or more vials) and antivenom was detected in all patients.

CONCLUSIONS

RBS AV given by the intramuscular route is unlikely to be effective in the treatment of redback (widow) spider bite.

Epidemiological and clinical characteristics of scorpionism in children in Sanliurfa, Turkey

The epidemiological and clinical findings of scorpion stings in Sanliurfa region of Turkey were evaluated in this investigation from May to September 2003, because of the high incidence of scorpionism cases during this season. Scorpion envenomation is an important health problem in all South-eastern Anatolia, specifically in Sanliurfa. The sting cases mostly occurred in the month of July (37.6%) when yearly temperature is the highest. Scorpion species causing the envenomation in children were not identified. More of the patients were adolescents (54.1%). Most of the stings were seen in exposed extremities (87.7%), mainly in the upper limbs (47.1%). One single village, Birecik, had the highest number of incidents (36.5%). Patients at the emergency units showed signs of local and systemic effects, but no lethality occurred. Local and autonomic nervous system effects were most frequently characterized by local pain, hyperemia, swelling, burning, hypotension, hypertension, dry mouth, thirst and sweating. We propose that public awareness and physician readiness combined with the availability of effective antivenom significantly reduced lethality in this region.

Naja kaouthia: Two cases of Asiatic cobra envenomations

Envenomation from cobra bites causes major morbidity and mortality in Asia and Africa but rarely in the United States. We describe two patients bitten by the Asiatic Cobra (Naja Kaouthia)--both successfully treated in the emergency department. Patient 1 was a 23-year-old woman bitten in the buttock by her cobra. Examination demonstrated two puncture wounds. She developed cranial neuropathy, respiratory failure, and coagulopathy 10 h later, necessitating endotracheal intubation and polyvalent antivenom administration. The patient recovered fully with minimal wound necrosis. Patient 2, a 44-year-old man, was bitten on the hand by his cobra. Examination revealed a puncture wound with progressive swelling. Edrophonium and monovalent antivenom were administered, and he recovered uneventfully. These cases emphasize the varied clinical presentations of the Asiatic cobra. Patient 1 developed delayed neurotoxicity, respiratory failure, and hematotoxicity with minimal wound necrosis, whereas Patient 2 experienced a more typical clinical course.

Arachnid toxinology in Australia: From clinical toxicology to potential applications

The unique geographic isolation of Australia has resulted in the evolution of a distinctive range of Australian arachnid fauna. Through the pioneering work of a number of Australian arachnologists, toxinologists, and clinicians, the taxonomy and distribution of new species, the effective clinical treatment of envenomation, and the isolation and characterisation of the many distinctive neurotoxins, has been achieved. In particular, work has focussed on several Australian arachnids, including red-back and funnel-web spiders, paralysis ticks, and buthid scorpions that contain neurotoxins capable of causing death or serious systemic envenomation. In the case of spiders, species-specific antivenoms have been developed to treat envenomed patients that show considerable cross-reactivity. Both in vitro and clinical case studies have shown they are particularly efficacious in the treatment of envenomation by spiders even from unrelated families. Despite their notorious reputation, the high selectivity and potency of a unique range of toxins from the venom of Australian arachnids will make them invaluable molecular tools for studies of neurotransmitter release and vesicle exocytosis as well as ion channel structure and function. The venoms of funnel-web spiders, and more recently Australian scorpions, have also provided a previously untapped rich source of insect-selective neurotoxins for the future development of biopesticides and the characterisation of previously unvalidated insecticide targets. This review provides a historical viewpoint of the work of many toxinologists to isolate and characterise just some of the toxins produced by such a unique group of arachnids and examines the potential applications of these novel peptides.

Medically important venomous animals: biology, prevention, first aid, and clinical management

Venomous animals are a significant health problem for rural populations in many parts of the world. Given the current level of the international mobility of individuals and the inquisitiveness of travelers, clinicians and travel clinics need to be able to give advice on the prevention, first aid, and clinical management of envenoming. Health professionals often feel overwhelmed by the taxonomy of venomous animals; however, venomous animals can be grouped, using a simple set of criteria, into cnidarians, venomous fish, sea snakes, scorpions, spiders, hymenoterans, and venomous terrestrial snakes. Geographic distribution, habitats, and circumstances of accidents further reduce the range of culprits that need to be considered in any single event. Clinical management of envenomed patients relies on supportive therapy and, if available, specific antivenoms. Supplies of life-saving antivenoms are scarce, and this scarcity particularly affects rural populations in resource-poor settings. Travel clinics and hospitals in highly industrialized areas predominantly see patients with injuries caused by accidents involving marine animals: in particular, stings by venomous fish and skin damage caused by jellyfish. However, globally, terrestrial venomous snakes are the most important group of venomous animals.

The efficacy of antivenom in loxoscelism treatment

Loxoscelism or brown spider envenomation is the most important form of araneism in some countries and constitutes the third cause of accidents by venomous animals in Brazil. The treatment of Loxosceles bites is still controversial, with a variety of interventions proposed and tried, such as antivenom. The majority of clinical studies demonstrate a significant delay between a spider's bite and presentation for treatment, and this delay is thought to lead to an ineffective administration of a specific antivenom. Even in Brazil, where the antivenom therapy has been indicated more frequently than in other countries, there are still doubts about its real capacity to neutralize local and systemic effects of the envenomation and the ideal period for its administration. Thus, various studies in animal models have tried to correlate the time of envenomation with the application of the antivenom and the permanence of the venom in circulation or in dermonecrotic lesions. The purpose of this study was to evaluate the use of antivenom in loxoscelism treatment and to systematize the results of studies in animals and humans available in the last 30 years, making possible a more critical analysis of the efficacy of the antivenom or its therapeutic value in bites by spiders of the genus Loxosceles.

Proteomic analysis of the venom and characterization of toxins specific for Na+- and K+-channels from the Colombian scorpion Tityus pachyurus

The Colombian scorpion Tityus pachyurus is toxic to humans and is capable of producing fatal accidents, but nothing is known about its venom components. This communication reports the separation of at least 57 fractions from the venom by high performance liquid chromatography. From these, at least 104 distinct molecular weight compounds were identified by mass spectrometry analysis. The complete amino acid sequences of three peptides were determined and the partial sequences of three others were also identified. Electrophysiological experiments conducted with ion-channels expressed heterologously on Sf9 cells showed the presence of a potent Shaker B K(+)-channel blocker. This peptide (trivial name Tpa1) contains 23 amino acid residues closely packed by three disulfide bridges with a molecular mass of 2,457 atomic mass units. It is the third member of the sub-family 13, for which the systematic name is proposed to be alpha-KTx13.3. The mice assay showed clearly the presence of toxic peptides to mammals. One of them named Tpa2, containing 65 amino acid residues with molecular mass of 7,522.5 atomic mass units, is stabilized by four disulfide bridges. It was shown to modify the Na(+)-currents of F-11 and TE671 cells in culture, similar to the beta scorpion toxins. These results demonstrate the presence of toxic peptides in the venom of T. pachyurus and confirm that accidents with this species of scorpion should be considered an important human hazard in Colombia.

Envenomations

Numerous types of envenomations may be encountered by health care workers depending on where in North America they work. Clinicians should be familiar with the animals in their region that may lead to envenomation.A rational approach with use of poison center or medical toxicology consultation services ensures that cases are managed appropriately.

Assessment of the viral safety of antivenoms fractionated from equine plasma

Antivenoms are preparations of intact or fragmented (F(ab′)₂ or Fab) immunoglobulin G (IgG) used in human medicine to treat the severe envenomings resulting from the bites and stings of various animals, such as snakes, spiders, scorpions, or marine animals, or from the contact with poisonous plants. They are obtained by fractionating plasma collected from immunized horses or, less frequently, sheep. Manufacturing processes usually include pepsin digestion at acid pH, papain digestion, ammonium sulphate precipitation, caprylic acid precipitation, heat coagulation and/or chromatography. Most production processes do not have deliberately introduced viral inactivation or removal treatments, but antivenoms have never been found to transmit viruses to humans. Nevertheless, the recent examples of zoonotic diseases highlight the need to perform a careful assessment of the viral safety of antivenoms.

This paper reviews the characteristics of equine viruses of antivenoms and discusses the potential of some manufacturing steps to avoid risks of viral contamination. Analysis of production parameters indicate that acid pH treatments and caprylic acid precipitations, which have been validated for the manufacture of some human IgG products, appear to provide the best potential for viral inactivation of antivenoms. As many manufacturers of antivenoms located in developing countries lack the resources to conduct formal viral validation studies, it is hoped that this review will help in the scientific understanding of the viral safety factors of antivenoms, in the controlled implementation of the manufacturing steps with expected impact on viral safety, and in the overall reinforcement of good manufacturing practices of these essential therapeutic products.

Direct vs. mediated effects of scorpion venom: an experimental study of the effects of a second challenge with scorpion venom

OBJECTIVE

To assess the respective roles of venom and of catecholamines following scorpion envenomation and to verify whether a second challenge with scorpion venom induces the same consequences than a first one.

DESIGN AND SETTING

Controlled animal study in a university research laboratory.

SUBJECTS

Anesthetized and ventilated dogs.

INTERVENTIONS

Fifteen dogs received intravenously a sublethal dose of scorpion venom (0.05 mg/kg). In the reenvenomated group (n=5) a second venom challenge with one-half sublethal venom dose was performed 30 min after the first one. The control group (n=10) received saline. Five additional animals served as sham.

MEASUREMENTS AND RESULTS

Plasma toxin and catecholamine levels and a set of usual hemodynamic measurements were repeatedly measured in the first hour following envenomation. In the reenvenomated group another set of measurements was performed 5 min after the second challenge. Changes in toxin, catecholamines, and the main hemodynamic parameters were compared between the study groups. Initial peak toxin levels were similar in the two groups. They induced a striking increase in circulating catecholamines, a fall in heart rate, and an increase in mean arterial and pulmonary artery occluded pressures and in systemic vascular resistance. In the reenvenomated group the second challenge with scorpion venom achieved a toxin blood level similar to the first peak. However, it was not associated with a significant effect either on catecholamines release or on hemodynamics. Subsequent trends in hemodynamic changes were similar to those observed in the control group.

CONCLUSIONS

These data emphasize the limited role of direct effects of scorpion venom on the cardiovascular system and the key role of catecholamines.

Morsures d’araignées : les aranéismes d’importance médicale

LIMITED RISKS: Although most species of spiders are venomous, only ten or so are able to induce human envenomations. From a systematic point of view, it is possible to distinguish the araneomorph spiders - or "true" spiders - from the mygalomorph spiders. Dangerous species for humans can be found in both groups. Regarding "true' spiders, two kinds of envenomation are frequent, ubiquitous and potentially severe: latrodectism (neurotoxic symptomatology) due to the Widow spiders of the Latrodectus species,and loxoscelism (viscero-cutaneous symptomatology). Regarding the mygalomorph spiders, the Australian species responsible for atraxism (neurotoxic symptomatology) are considered as the most dangerous. Most of the other mygalomorph spiders, when they bite, only provoke benign loco regional problems. A supplementary defensive weapon exists in certain South-American species: urticating hairs which may induce severe ocular damage.

Brown spiders and loxoscelism

Accidents caused by brown spiders (Loxosceles genus) are classically associated with dermonecrotic lesions and systemic manifestations including intravascular haemolysis, disseminated intravascular coagulation and acute renal failure. Systemic reactions occur in a minority of cases, but may be severe in some patients and occasionally fatal. The mechanisms by which Loxosceles venom exerts these noxious effects are currently under investigation. The venom contains several toxins, some of which have been well-characterised biochemically and biologically. The purpose of the present review is to describe some insights into loxoscelism obtained over the last ten years. The biology and epidemiology of the brown spider, the histopathology of envenomation and the immunogenicity of Loxosceles venom are reviewed, as are the clinical features, diagnosis and therapy of brown spider bites. The identification and characterisation of some toxins and the mechanism of induction of local and systemic lesions caused by brown spider venom are also discussed. Finally, the biotechnological application of some venom toxins are covered.

Loxoscelism: Old obstacles, new directions

Loxosceles spiders have a worldwide distribution and are considered one of the most medically important groups of spiders. Envenomation (loxoscelism) can result in dermonecrosis and, less commonly, a systemic illness that can be fatal. The mechanism of venom action is multifactorial and incompletely understood. The characteristic dermonecrotic lesion results from the direct effects of the venom on the cellular and basal membrane components, as well as the extracellular matrix. The initial interaction between the venom and tissues causes complement activation, migration of polymorphic neutrophils, liberation of proteolytic enzymes, cytokine and chemokine release, platelet aggregation, and blood flow alterations that result in edema and ischemia, with development of necrosis. There is no definitive treatment for loxoscelism. However, animal model studies suggest the potential value of specific antivenom to decrease lesion size and limit systemic illness even when such administration is delayed.

Clinical consequences of spider bites: recent advances in our understanding

Spider bite continues to be a controversial subject worldwide and attribution of clinical effects to different spiders is problematic because of poor case definition and paucity of clinical evidence. The effects of medically important spiders are sometimes underestimated and simultaneously there is misattribution of effects to harmless spider groups. The majority of suspected spider bites present as skin lesions or necrotic ulcers where the history of a spider bite must be confirmed. To be a definite spider bite, the patient must immediately observe the spider and there be evidence of the bite, such as pain. Important groups of spiders worldwide include the widow spiders (latrodectism), recluse spiders (loxoscelism) and some mygalomorph spiders including the Australian Funnel web spider. Most spiders only cause minor effects, including a large number of groups that have been implicated in necrotic arachnidism.

Arthropods in dermatology

Arthropods are important in medicine for a multitude of reasons. Their bites and stings may induce allergic reactions, ranging from annoying to life-threatening. Many arthropod products are also capable of inciting allergic responses in sensitized persons. In recent years, bites and stings have gained greater attention owing to increased concern about disease transmission. A common hypersensitivity response to arthropod bites, stings, and products is papular urticaria. This eruption occurs primarily in children, who eventually "outgrow" this disease, probably through desensitization after multiple arthropod exposures. Papular urticaria is most often caused by fleas or bedbugs, but virtually any arthropod is capable of inducing such a reaction. Two arthropod classes of medical importance are the Arachnida (spiders, scorpions, ticks, and mites) and the Insecta (lice, fleas, bedbugs, flies, bees, and ants). Animals in these two classes are probably responsible for more morbidity and mortality worldwide than are any other group of venomous creatures. In general, the diagnosis of arthropod bites and stings is dependent on maintenance of a high index of suspicion and familiarity with the arthropod fauna not only in one's region of practice, but also in the travel regions of one's patients. Learning objective At the completion of this learning activity, participants should be familiar with the clinical manifestations caused by a variety of arthropods as well as the treatment and possible sequelae of arthropod attacks.