Intradermal anti-loxosceles Fab fragments attenuate dermonecrotic arachnidism

Brown Spider Venom Phospholipases D: From Potent Molecules Involved in Pathogenesis of Brown Spider Bites to Molecular Tools for Studying Ectosomes, Ectocytosis, and Its Applications

Accidents caused by Loxosceles spiders, commonly known as brown spiders, are frequent in warm and temperate regions worldwide, with a higher prevalence in South America and the southern United States. In the venoms of species clinically associated with accidents, phospholipases D (PLDs) are the most expressed toxins. This classification is based on the toxins' ability to cleave various phospholipids, with a preference for sphingomyelin. Studies using purified PLDs have demonstrated that these enzymes cleave phospholipids from cells, producing derivatives that can activate leukocytes. A dysregulated inflammatory response is the primary effect following envenomation, leading to dermonecrosis, which is histopathologically characterized by aseptic coagulative necrosis-a key feature of envenomation. Although advances in understanding the structure-function relationship of enzymes have been achieved through molecular biology, heterologous expression, site-directed mutations, crystallography, and bioinformatic analyses-describing PLDs in the venoms of various species and highlighting the conservation of amino acid residues involved in catalysis, substrate binding, and magnesium stabilization-little is known about the cellular biology of these PLDs. Studies have shown that the treatment of various cells with recombinant PLDs stimulates the formation of ectosomes and ectocytosis, events that initiate a cascade of intracellular signaling in PLD-binding cells and lead to the release of extracellular microvesicles. These microvesicles may act as signalosomes for other target cells, thereby triggering an inflammatory response and dermonecrosis. In this review, we will discuss the biochemical properties of PLDs, the target cells that bind to them, and the ectocytosis-dependent pathophysiology of envenoming.

Prospective Use of Brown Spider Venom Toxins as Therapeutic and Biotechnological Inputs

Brown spider (genus Loxosceles) venoms are mainly composed of protein toxins used for predation and defense. Bites of these spiders most commonly produce a local dermonecrotic lesion with gravitational spread, edema and hemorrhage, which together are defined as cutaneous loxoscelism. Systemic loxoscelism, such as hematological abnormalities and renal injury, are less frequent but more lethal. Some Loxosceles venom toxins have already been isolated and extensively studied, such as phospholipases D (PLDs), which have been recombinantly expressed and were proven to reproduce toxic activities associated to the whole venom. PLDs have a notable potential to be engineered and converted in non-toxic antigens to produce a new generation of antivenoms or vaccines. PLDs also can serve as tools to discover inhibitors to be used as therapeutic agents. Other Loxosceles toxins have been identified and functionally characterized, such as hyaluronidases, allergen factor, serpin, TCTP and knottins (ICK peptides). All these toxins were produced as recombinant molecules and are biologically active molecules that can be used as tools for the potential development of chemical candidates to tackle many medical and biological threats, acting, for instance, as antitumoral, insecticides, analgesic, antigens for allergy tests and biochemical reagents for cell studies. In addition, these recombinant toxins may be useful to develop a rational therapy for loxoscelism. This review summarizes the main candidates for the development of drugs and biotechnological inputs that have been described in Brown spider venoms.

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.

Brown Recluse Spider Bites in Patients With Neutropenia: A Single-institution Experience

Brown recluse spider bites can cause local and systemic signs, including rash, dermonecrosis, edema, hemolysis, and acute kidney failure. These are mostly attributed to sphingomyelinase D, the main toxin. To evaluate the severity of the disease in pediatric patients with and without neutropenia, we retrospectively reviewed records of patients treated at St. Jude Children's Research Hospital between 1970 and 2015 and identified 19 patients who met the inclusion criteria. Variables of interest included the type of underlying illness, presence of neutropenia, number of days of hospitalization, disease signs and outcome of the bite, and treatments administered. We used descriptive statistics to summarize the manifestations and severity of spider bites in patients with and without neutropenia. Six patients experienced pain from the bite, 11 had erythema, 7 developed edema, and 5 had fever. The response to spider bites in neutropenic patients was no milder than that in non-neutropenic individuals. Six patients developed systemic complications. Compared with non-neutropenic patients, neutropenic patients had antibiotics prescribed more often and experienced longer hospital stays. Spider bites do not seem to have a different clinical course in neutropenic patients. Therefore, a conservative approach may be best for these patients, with close monitoring and local wound care.

Low Health System Performance, Indigenous Status and Antivenom Underdosage Correlate with Spider Envenoming Severity in the Remote Brazilian Amazon

Background

A better knowledge of the burden and risk factors associated with severity due to spider bites would lead to improved management with a reduction of sequelae usually seen for this neglected health problem, and would ensure proper use of antivenoms in remote localities in the Brazilian Amazon. The aim of this study was to analyze the profile of spider bites reported in the state of Amazonas in the Western Brazilian Amazon, and to investigate potential risk factors associated with severity of envenomation.

Methodology/Principal Findings

We used a case-control study in order to identify factors associated with spider bite severity in the Western Brazilian Amazon from 2007 to 2014. Patients evolving to any severity criteria were considered cases and those with non-severe bites were included in the control group. All variables were retrieved from the official Brazilian reporting systems. Socioeconomical and environmental components were also included in a multivariable analysis in order to identify ecological determinants of incidence and severity. A total of 1,181 spider bites were recorded, resulting in an incidence of 4 cases per 100,000 person/year. Most of the spider bites occurred in males (65.8%). Bites mostly occurred in rural areas (59.5%). The most affected age group was between 16 and 45 years old (50.9%). A proportion of 39.7% of the bites were related to work activities. Antivenom was prescribed to 39% of the patients. Envenomings recorded from urban areas [Odds ratio (OR) = 0.40 (95%CI = 0.30–0.71; p<0.001)] and living in a municipality with a mean health system performance index (MHSPI >median [OR = 0.64 (95%CI = 0.39–0.75; p<0.001)] were independently associated with decreased risk of severity. Work related accidents [OR = 2.09 (95%CI = 1.49–2.94; p<0.001)], Indigenous status [OR = 2.15 (95%CI = 1.19–3.86; p = 0.011)] and living in a municipality located >300 km away from the state capital Manaus [OR = 1.90 (95%CI = 1.28–2.40; p<0.001)] were independently associated with a risk of severity. Living in a municipality located >300 km away from the state capital Manaus [OR = 1.53 (95%CI = 1.15–2.02; p = 0.003)] and living in a municipality with a MHSPI <median [OR = 1.91 (95%CI = 1.28–2.47; p = 0.002)] increased the odds of antivenom underdosage.

Conclusions

Spider bites is prevalent across the study region with a higher incidence in the rainy season in rural areas. Spider bites can be painful and lead to local manifestations but rarely result in life-threatening envenoming. Major local complications were dermonecrosis and secondary infection in cases diagnosed as Loxosceles bites. Based on the correlations shown here, envenomings occurring in remote rural areas, Indigenous status and living in a municipality located >300 km away from the state capital Manaus could be contributing factors to higher severity of spider envenomings in this area, as well as to antivenom underdosage.

Targeted localized use of therapeutic antibodies: a review of non-systemic, topical and oral applications

Therapeutic antibodies provide important tools in the "medicine chest" of today's clinician for the treatment of a range of disorders. Typically monoclonal or polyclonal antibodies are administered in large doses, either directly or indirectly into the circulation, via a systemic route which is well suited for disseminated ailments. Diseases confined within a specific localized tissue, however, may be treated more effectively and at reduced cost by a delivery system which targets directly the affected area. To explore the advantages of the local administration of antibodies, we reviewed current alternative, non-systemic delivery approaches which are in clinical use, being trialed or developed. These less conventional approaches comprise: (a) local injections, (b) topical and (c) peroral administration routes. Local delivery includes intra-ocular injections into the vitreal humor (i.e. Ranibizumab for age-related macular degeneration), subconjunctival injections (e.g. Bevacizumab for corneal neovascularization), intra-articular joint injections (i.e. anti-TNF alpha antibody for persistent inflammatory monoarthritis) and intratumoral or peritumoral injections (e.g. Ipilimumab for cancer). A range of other strategies, such as the local use of antibacterial antibodies, are also presented. Local injections of antibodies utilize doses which range from 1/10th to 1/100th of the required systemic dose therefore reducing both side-effects and treatment costs. In addition, any therapeutic antibody escaping from the local site of disease into the systemic circulation is immediately diluted within the large blood volume, further lowering the potential for unwanted effects. Needle-free topical application routes become an option when the condition is restricted locally to an external surface. The topical route may potentially be utilized in the form of eye drops for infections or corneal neovascularization or be applied to diseased skin for psoriasis, dermatitis, pyoderma gangrenosum, antibiotic resistant bacterial infections or ulcerated wounds. Diseases confined to the gastrointestinal tract can be targeted directly by applying antibody via the injection-free peroral route. The gastrointestinal tract is unusual in that its natural immuno-tolerant nature ensures the long-term safety of repeatedly ingesting heterologous antiserum or antibody materials. Without the stringent regulatory, purity and clean room requirements of manufacturing parenteral (injectable) antibodies, production costs are minimal, with the potential for more direct low-cost targeting of gastrointestinal diseases, especially with those caused by problematic antibiotic resistant or toxigenic bacteria (e.g. Clostridium difficile, Helicobacter pylori), viruses (e.g. rotavirus, norovirus) or inflammatory bowel disease (e.g. ulcerative colitis, Crohn's disease). Use of the oral route has previously been hindered by excessive antibody digestion within the gastrointestinal tract; however, this limitation may be overcome by intelligently applying one or more strategies (i.e. decoy proteins, masking therapeutic antibody cleavage sites, pH modulation, enzyme inhibition or encapsulation). These aspects are additionally discussed in this review and novel insights also provided. With the development of new applications via local injections, topical and peroral routes, it is envisaged that an extended range of ailments will increasingly fall within the clinical scope of therapeutic antibodies further expanding this market.

Spider bite

Spiders are a source of intrigue and fear, and several myths exist about their medical effects. Many people believe that bites from various spider species cause necrotic ulceration, despite evidence that most suspected cases of necrotic arachnidism are caused by something other than a spider bite. Latrodectism and loxoscelism are the most important clinical syndromes resulting from spider bite. Latrodectism results from bites by widow spiders (Latrodectus spp) and causes local, regional, or generalised pain associated with non-specific symptoms and autonomic effects. Loxoscelism is caused by Loxosceles spp, and the cutaneous form manifests as pain and erythema that can develop into a necrotic ulcer. Systemic loxoscelism is characterised by intravascular haemolysis and renal failure on occasion. Other important spiders include the Australian funnel-web spider (Atrax spp and Hadronyche spp) and the armed spider (Phoneutria spp) from Brazil. Antivenoms are an important treatment for spider envenomation but have been less successful than have those for snake envenomation, with concerns about their effectiveness for both latrodectism and loxoscelism.

Brown recluse spider (Loxosceles reclusa) envenomation in small animals

OBJECTIVE

To provide a comprehensive review of relevant literature regarding the brown recluse spider (BRS) and to define those criteria that must be satisfied before making a diagnosis of brown recluse envenomation.

ETIOLOGY

The complex venom of the BRS contains sphingomyelinase D, which is capable of producing all the clinical signs in the human and some animal models.

DIAGNOSIS

There is no current commercially available test. In humans there are many proposed guidelines to achieve a definitive diagnosis; however, there are no established guidelines for veterinary patients.

THERAPY

Currently, no consensus exists for treatment of BRS envenomation other than supportive care, which includes rest, thorough cleaning of the site, ice, compression, and elevation.

PROGNOSIS

Prognosis varies based on severity of clinical signs and response to supportive care.

An in vivo protective response against toxic effects of the dermonecrotic protein from Loxosceles intermedia spider venom elicited by synthetic epitopes

Loxoscelism is a necrotic-hemolytic syndrome caused by bites of brown spiders belonging to the genus Loxosceles. Many approaches for the treatment of Loxosceles poisoning have already been proposed, among which administration of specific antivenom is thought to be the more specific. We have evaluated the use of peptides as immunogen to raise in rabbits an antibody response that could protect animals from a challenge by the Loxtox isoform LiD1, one of the main toxic component of Loxosceles intermedia venom. Six antigenic regions of LiD1 were mapped by using the SPOT method. The corresponding peptides were further chemically synthesized, mixed, and used as immunogens in rabbits. Control animal received recombinant LiD1 alone or together with peptides. We found that the rabbit antibody response to peptides was cross-reactive with LiD1, although only one peptide from the mix of six was immunogenic. The dermonecrotic, hemorrhagic and oedema forming activities induced by LiD1 in naïve rabbits were inhibited by 82%, 35% and 35% respectively, by preincubation of LiD1 with anti-peptide antibodies prepared from immunized rabbits. Animals that were immunized with peptides or LiD1r, were found to be protected from the dermonecrotic, hemorrhagic and oedema forming activities induced by a challenge with LiD1. The protection conferred by peptides was, however, lower than that provided by the peptide protein combination or by the full-length protein. These results encourage us in the utilization of synthetic peptides for therapeutic serum development or vaccination approaches.

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.

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.

Role of IgG(T) and IgGa isotypes obtained from arachnidic antivenom to neutralize toxic activities of Loxosceles gaucho, Phoneutria nigriventer and Tityus serrulatus venoms

The ability of IgG(T) and IgGa subclasses--isolated by liquid chromatography from equine arachnidic antivenom (AAV)-to neutralize toxic activities of Loxosceles gaucho, Phoneutria nigriventer and Tityus serrulatus venoms as well as to remove venom toxins from circulation was investigated. These subclasses showed similar antibody titers against L. gaucho, P. nigriventer and T. serrulatus venoms, and by immunoblotting few differences were observed in the recognition pattern of venom antigens. IgG(T) and IgGa neutralized 100% lethality induced by L. gaucho and 50% of P. nigriventer venom, but IgGa failed to neutralize T. serrulatus venom, in contrast to IgG(T). Both subclasses neutralized local reactions and dermonecrosis induced by L. gaucho venom in rabbits. In mice, IgG(T) and IgGa partially neutralized the edematogenic activity induced by P. nigriventer and T. serrulatus venoms, but only IgG(T) neutralized (ca. 81%) the nociceptive activity induced by T. serrulatus venom. Both subclasses failed to neutralize nociceptive activity induced by P. nigriventer venom. IgG(T) reduced the serum venom levels of animals injected with L. gaucho, P. nigriventer or T. serrulatus venoms, while IgGa solely reduced L. gaucho and P. nigriventer venoms levels. Our results demostrate that IgG(T) and IgGa subclasses neutralize toxic activities induced by P. nigriventer, T. serrulatus and L. gaucho venoms with different efficacies, as well as depurate these venoms from circulation.

Brown Recluse Spider Envenomation

Brown recluse spider bite is a common diagnosis in almost every state in America. In fact, cases have been reported in areas where the spider has never been seen. A review of medical literature reveals that most current concepts regarding brown recluse spider envenomation are based on supposition. In this article, we attempt to review critically our present understanding of brown recluse bites with a focus on the published evidence.

Enzymatic characterization, antigenic cross-reactivity and neutralization of dermonecrotic activity of five Loxosceles spider venoms of medical importance in the Americas

Loxosceles spiders have a wide distribution in the temperate and tropical regions of the world. Loxoscelism is characterized by necrotic skin ulceration at the bite site and, less commonly, a systemic illness that may be fatal. The purpose of this study was to characterize and compare aspects of the major medically important Loxosceles spider venoms in a standardized manner, particularly considering their neutralization by two Brazilian antivenoms. By SDS-PAGE (12% acrylamide), Loxosceles deserta, Loxosceles gaucho, Loxosceles intermedia, Loxosceles laeta and Loxosceles reclusa venoms had similar electrophoretic profiles, with the major protein bands of 32-35 kDa. All venoms exhibited gelatinolytic, caseinolytic and fibrinogenolytic activities in vitro with a large array of proteases, mainly between 18.1 and 31.8 kDa. Most of these enzymes were metalloproteases as this activity was abolished by 1,10-phenanthroline. Hyaluronidase activity was detected in a protein band of approximately 44 kDa in all venoms. Sphingomyelinase activity was demonstrated in all five venoms. Antigenic cross-reactivity, by Western blotting, was also observed among all venoms studied using commercial equine antivenoms produced in Brazil (Institute Butantan and CPPI). These antivenoms recognized mainly components between 25 and 40 kDa in all venoms with several minor components of >89 kDa. Strong cross-reactivity was also seen among all venoms through the ELISA technique (titre range: 64,000-512,000). All venoms (5 microg doses) induced a similar local reaction when injected intradermally into the flank of rabbits, demonstrating dermonecrosis, hemorrhage, vasoconstriction, edema, and erythema. However, no reaction was observed when each venom was pre-incubated (1 h, 37 degrees C) with Brazilian commercial sera prior to injection. The antivenoms also abolished the sphingomyelinase activity in vitro, suggesting the venoms of the major medically important Loxosceles spider species have generally similar toxic and enzymatic characteristics. Thus, as Brazilian commercial antivenoms are able to neutralize the dermonecrosis induced by Loxosceles venoms of diverse geographical origin, clinical studies should be undertaken on the potential for a single global Loxosceles antivenom.

Survey for potentially necrotizing spider venoms, with special emphasis on Cheiracanthium mildei

It has proven difficult to identify those spiders which cause necrotic lesions. In an effort to design a simple, inexpensive screening method for identifying spiders with necrotizing venoms, we have examined the venom gland homogenates of a variety of spider species for their ability to cause red blood cell lysis. Those venoms which were positive were further examined for the presence of sphingomyelinase D, and their ability to evoke necrotic lesions in the skin of rabbits. Sphingomyelinase D is known to be the causative agent of necrosis and red blood cell lysis in the venom of the brown recluse spider (Loxosceles reclusa), and our assumption was that this would be the same agent in other spider venoms as well. This did not prove to be the case. Of 45 species examined, only the venom of L. reclusa and Cheiracanthium mildei lysed sheep red blood cells. Unlike L. reclusa venom, however, C. mildei venom did not possess sphingomyelinase D nor did it cause necrotic lesions in the skin of rabbits. We present evidence suggesting that a phospholipase A2 is the hemolytic agent in C. mildei venom.

Life-threatening stings, bites, infestations, and parasitic diseases

Bites, stings and infestations can be fatal. Anaphylaxis to vespids and bees can be prevented with immunotherapy. Patients should be referred to an allergist. The acute care and prevention of arthropod injury is discussed below.

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.

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.

Pharmacokinetic-pharmacodynamic relationships of immunoglobulin therapy for envenomation

Parenteral administration of horse- and sheep-derived antivenoms constitutes the cornerstone in the therapy of envenomations induced by animal bites and stings. Depending on the type of neutralising molecule, antivenoms are made of: (i) whole IgG molecules (150 kDa), (ii) F(ab')(2) immunoglobulin fragments (100 kDa) or (iii) Fab immunoglobulin fragments (50 kDa). Because of their variable molecular mass, these three types of antivenoms have different pharmacokinetic profiles. Fab fragments have the largest volume of distribution and readily reach extravascular compartments. They are catabolised mainly by the kidney, having a more rapid clearance than F(ab')(2) fragments and IgG. On the other hand, IgG molecules have a lower volume of distribution and a longer elimination half-life, showing the highest cycling through the interstitial spaces in the body. IgG elimination occurs mainly by extrarenal mechanisms. F(ab')(2) fragments display a pharmacokinetic profile intermediate between those of Fab fragments and IgG molecules. Such diverse pharmacokinetic properties have implications for the pharmacodynamics of these immunobiologicals, since a pronounced mismatch has been described between the pharmacokinetics of venoms and antivenoms. Some venoms, such as those of scorpions and elapid snakes, are rich in low-molecular-mass neurotoxins of high diffusibility and large volume of distribution that reach their tissue targets rapidly after injection. In contrast, venoms rich in high-molecular-mass toxins, such as those of viperid snakes, have a pharmacokinetic profile characterised by a rapid initial absorption followed by a slow absorption process from the site of venom injection. Such delayed absorption has been linked with recurrence of envenomation when antibody levels in blood decrease. This heterogeneity in pharmacokinetics and mechanism of action of venom components requires a detailed analysis of each venom-antivenom system in order to determine the most appropriate type of neutralising molecule for each particular venom. Besides having a high affinity for toxicologically relevant venom components, an ideal antivenom should possess a volume of distribution as similar as possible to that of the toxins being neutralised. Moreover, high levels of neutralising antibodies should remain in blood for a relatively prolonged time to assure neutralisation of toxins reaching the bloodstream later in the course of envenomation, and to promote redistribution of toxins from extravascular compartments to blood. Additional studies are required on different venoms and antivenoms in order to further understand the pharmacokinetic-pharmacodynamic relationships of antibodies and their fragments and to optimise the immunotherapy of envenomations.

Sudden unexplained hemolysis occurring in an infant due to presumed Loxosceles envenomation

We report the case of a 3-week-old infant referred for evaluation of sudden onset jaundice and unexplained hemolysis. After an exhaustive workup, the most likely etiology was found to be envenomation by a brown recluse spider, Loxosceles reclusa. This case underscores the fact that severe loxoscelism may occur in the absence of the classically described necrotic cutaneous lesion, and represents one of the youngest presumed cases of loxoscelism. We present the case to illustrate the importance of considering loxoscelism in the differential diagnosis of sudden massive hemolysis in children, particularly in endemic areas of the midwestern and southern United States.

Antivenom treatment in arachnidism

Envenomation by arachnids causes significant medical illness worldwide. Scorpion sting is the most important arachnid envenomation causing adult morbidity and pediatric mortality. Important groups of spiders include the widow spiders (Latrodectus spp.), the recluse spiders (Loxosceles spp.), and two spiders confined to single countries: the Australian funnel web spider (Atrax and Hadronyche spp.) and the armed spider (Phoneutria spp.) from Brazil. There are four widow spider antivenoms available, including the Australian redback spider antivenom and the American black widow antivenom. Despite good in vitro animal work demonstrating effective neutralization with these antivenoms, and cross-reactivity between many species, there continues to be a reluctance to use them in some countries. They are both associated with a relatively low rate of allergic reactions. Redback antivenom is routinely used by the intramuscular route, which may not be as effective as intravenous use based on clinical experience and animal studies. Antivenoms are available for Loxosceles spp., but there is little evidence to support their effectiveness, particularly against local effects. The Australian funnel web spider causes severe neurotoxic envenomation, and antivenom appears to be effective in reported cases. An antivenom exists for the Brazilian armed spider, but is used in only a minority of cases. Many scorpion antivenoms exist worldwide, but there remains significant controversy regarding their efficacy. Animal and human venom level studies demonstrate neutralization of circulating venom in systemic envenomation. Clinical experience in countries where antivenom has been introduced suggests it has reduced pediatric mortality. However, three controlled trials demonstrated that antivenom was not effective, but these included few severe cases. Until controlled trials of antivenom in systemically envenomated patients are undertaken, antivenom use appears justified in severe envenomation. Although envenomation from arthropods is common, no antivenoms exist for these, excepting Lonomia caterpillars in South America, and Ixodes paralysis ticks in Australia.

Intramuscular administration of antivenoms in experimental envenomation by Bothrops asper: comparison between Fab and IgG

The efficacy of intramuscular (im) administration of sheep Fab and IgG antivenoms was assessed in a mouse experimental model of envenomation by Bothrops asper, in order to test if the more rapid absorption of Fab improves neutralization. Both antivenoms were adjusted to have a similar neutralizing potency in assays involving preincubation of venom and antivenom. Neither antivenom was effective in neutralizing lethality, nor in prolonging the time of death, in mice injected with either 3, 2 or 1.5 LD(50)s of venom by the intraperitoneal (ip) route, in experiments in which antivenoms were administered im immediately after envenomation. Antivenoms were effective in the neutralization of defibrinating activity, even if treatment was performed 30 min after envenomation, with no differences between IgG and Fab. Regarding neutralization of local effects, i.e. myonecrosis and hemorrhage, im administration of antivenoms at a site distant from the venom-injection site was completely ineffective in reducing the extent of local tissue damage. However, partial neutralization of these effects was achieved if antivenoms were administered im at the same site of venom injection, provided treatment was performed immediately after envenomation. Fab antivenom was slightly more effective than IgG antivenom in the neutralization of myotoxicity under these conditions, although a similar efficacy was observed between these antivenoms regarding neutralization of hemorrhagic effect. Our observations do not evidence major differences in the neutralizing ability of Fab and IgG antivenoms when applied by the im route, and do not support the hypothesis that im administration of Fab antivenoms constitutes an effective alternative to treat B. asper envenomations.

A new assay for the detection of Loxosceles species (brown recluse) spider venom

STUDY OBJECTIVE

Dermal lesions from unrelated arthropod species and medical causes appear similar to Loxosceles species (brown recluse spider) bites. This may result in delayed diagnosis and treatment. We developed a sensitive Loxosceles species venom enzyme-linked immunosorbent assay (ELISA) and characterized the specificity of the assay by evaluating antigenic cross-reactivity from a variety of North American arthropod venoms.

METHODS

North American arthropod (14 spiders, 2 scorpions, and 1 bee) venoms were studied. Three venom amounts (diluted in 100 microL of ELISA buffer) were assayed: 16,000 ng, 2,000 ng, and 40 ng. The latter quantity was selected because this is the observed maximum amount of venom we detect when inoculating dermis with amounts likely to be deposited by a spider bite. The larger venom amounts are overwhelming quantities designed to test the limits of the assay for arthropod venom cross-reactivity. Similar amounts of Loxosceles species venom and bovine albumin served as positive and negative controls, respectively.

RESULTS

At the lowest amount of venom tested (40 ng), the ELISA detected only the Loxosceles species positive control. When 2,000 ng was assayed, only Scytodes fusca and Kukulcania hibernalis arachnid venoms (in addition to Loxosceles species) cross-reacted to the assay. Finally, at 16,000 ng, the ELISA assay modestly detected Diguetia canities, Heteropoda venatoria, Tegenaria agrestis, Plectreurys tristes, Dolomedes tenebrosus, and Hadrurus arizonensis arachnid venoms.

CONCLUSION

Cross-reactivity was observed in 8 of 17 North American arthropod venoms when large venom amounts were assayed with a Loxosceles species ELISA. By using a relevant quantity of venom, 40 ng, the assay was specific for Loxosceles species venom. The venom specificity of the ELISA may allow clinical application in Loxosceles species endemic regions of North America.

Detection of Loxosceles species venom in dermal lesions: a comparison of 4 venom recovery methods

STUDY OBJECTIVE

Loxosceles species spider envenomations may produce necrotic, disfiguring dermal inflammatory lesions resembling neutrophilic dermatoses. With definitive treatment options lacking, clinicians are reluctant to obtain invasive biopsy specimens for diagnostic analysis. We compared less invasive venom collection methods and determined the time limit after inoculation for feasible venom recovery in an animal model.

METHODS

Nine New Zealand rabbits were randomized to 1 of 3 groups (n=3). Groups 1 and 2 were inoculated intradermally with 3 microg of L reclusa venom at 5 inoculation sites per rabbit. Albumin (3 microg) was injected intradermally in each rabbit as a negative control. Hair (group 1) and aspirate samples (group 2) were collected (1 time per site) over a 1-week period after inoculation. Group 3 was inoculated with 3 microg of Loxosceles species venom on 1 flank and 3 microg of albumin on the opposite flank. Daily serum specimens were collected over a 7-day period. On day 7, dermal punch biopsy specimens were taken from the venom and control inoculation sites. Hair, aspirate, biopsy, and serum specimens were assayed for venom by using an enzyme-linked immunosorbent assay. A generalized linear model was fit with the generalized estimating equation method to estimate the mean differences between groups.

RESULTS

Venom was detected in hair, aspirate, and biopsy specimens on all days of the study period. Hair samples yielded venom recovery on day 1 (median 0.062 ng/100 microL; mean difference 0.054 ng/100 microL; 95% confidence interval [CI] 0.048 to 0.059) through day 7 (median 0.020 ng/100 microL; mean difference 0.020 ng/100 microL; 95% CI 0.013 to 0.027). Aspirates were positive for venom recovery on day 1 (median 0.275 ng/100 microL; mean difference 0.231 ng/100 microL; 95% CI 0.192 to 0.271) through day 7 (median 0.0 ng/100 microL; mean difference 0.032 ng/100 microL; 95% CI -0.18 to 0.078). The highest venom yield was from the biopsy specimens (median 1.75 ng/100 microL; mean difference 0.041 ng/100 microL; 95% CI 0.033 to 0.027). Venom was undetectable in all serum samples.

CONCLUSION

Loxosceles species venom is detectable in hair, aspirate, and dermal biopsy specimens at least 7 days after venom inoculation and undetectable in serum by using the rabbit model.

Neutralization of dermonecrotic and lethal activities and differences among 32-35 kDa toxins of medically important Loxosceles spider venoms in Brazil revealed by monoclonal antibodies

Neutralization of dermonecrotic and lethal activities and differences among the principal toxic proteins (32-35 kDa) of medically important Loxosceles spider venoms in Brazil (Loxosceles gaucho, Loxosceles laeta and Loxosceles intermedia) were studied using monoclonal antibodies (MAbs) produced against the dermonecrotic component (35 kDa) of L. gaucho venom. MAb titers were 512,000 to homologous venom, between 2000 and 64,000 for L. intermedia venom and between 1000 and 64,000 for L. laeta venom. By Western blotting, MAbs could recognize mainly the 35 kDa protein of L. gaucho venom and with less intensity the 35 kDa protein of L. intermedia venom. These MAbs also recognized weakly or did not recognize the 32 kDa component of L. laeta venom. Only MoALg1 showed high affinity for L. gaucho venom and neutralized in vivo 90-97% of the dermonecrotic activity, besides delaying the lethality induced by homologous venom. MoALg1 maintained its capacity to neutralize the dermonecrotic activity, even when administered (i.v.) 6h after envenoming (i.d.). All MAbs obtained failed to neutralize the toxic activities of the heterologous venoms.These results suggest that different epitopes are present in the protein responsible for the dermonecrotic activity of Loxosceles venoms, and confirm the participation of other venom components during the local reaction process. This study also confirms the importance of antibodies for neutralization of dermonecrotic activity, even when administered some hours after envenoming, and emphasizes the differences of composition and toxicity of medically important Loxosceles venoms. These findings must be considered in order to improve loxoscelism immunotherapy.

Antigenic cross-reactivity of venoms from medically important North American Loxosceles spider species

We characterized the antigenic cross-reactivity of two medically important North American Loxoxceles species: L. reclusa (native to southeastern US) and L. deserta (native to southwestern US). Dermonecrosis resulting from bites from these two North American spider species are indistinguishable clinically. Polyclonal IgG antivenins directed against L. reclusa and L. deserta were raised in rabbits and used to develop specific enzyme immunoassays (EIAs). Antigenic differences in the two venoms were evaluated as follows: (1) Comparison of the sensitivities and correlation coefficient (R(2)) of anti-L. reclusa (alpha LoxR) and anti-L. deserta antibodies (alpha LoxD) in the detection of varying concentrations of the two venoms; (2) separation and western blot comparison of venom components; (3) protein sequence analysis of L. desertavenom and comparison to the L. reclusa protein sequence analysis present in a US national database; and (4) in vivo evaluation of alpha LoxR and alpha LoxD antivenins in attenuating dermal lesions (rabbit model). Correlation coefficients for alpha LoxR (R(2)=0.99) and alpha LoxD (R(2)=0.99) polyclonal antibodies in the measurements of standard concentrations of venoms were virtually identical. Western blot analysis revealed multiple common bands between the two venoms. Amino acid data (amino acids 1-35, N-terminal) of the active venom components of the two venoms revealed only three non-identical amino acids. alpha LoxR and alpha LoxD antivenins were similarly effective in blocking the development of rabbit skin lesions (ANOVA p<0.05). In summary, L. reclusa and L deserta spider venoms possess several common protein bands as identified by western blot, greater than 90% amino acid sequence identity, and marked antigenic cross-reactivity.

Direct correlation between diffusion of Loxosceles reclusa venom and extent of dermal inflammation

OBJECTIVES

Envenomation by Loxosceles species (brown recluse) spiders results in large dermal inflammatory lesions. Venom-induced dermal inflammation occurs indirectly via soluble mediators of inflammation. This study aimed to explore whether the anatomic extent of dermonecrotic arachnidism is due to the cascade of soluble proinflammatory mediators elicited by venom deposited at the bite site, or due to diffusion of the venom per se.

METHODS

Three New Zealand white rabbits received intradermal L. reclusa venom (3-microg) injections in the flank. At the time of maximum dermal inflammation (24 hr), paired 4-mm dermal biopsies were obtained in 2-cm intervals extending 0 to 12 cm from the inoculation site. Normal dermal tissue was obtained from the opposite flank to serve as a negative control. One biopsy sample from each interval was homogenized and assayed for myeloperoxidase (MPO) activity and for the presence of venom via an enzyme immunoassay (EIA). The other paired dermal biopsy was sectioned, and examined for the presence of polymorphonuclear neutrophils (PMNs) by microscopy. Lesional areas were measured using digital images imported into imaging software.

RESULTS

Mean +/- SD lesional diameter 24 hours post inoculation measured 9.18 +/- 0.64 cm. Venom was detected in biopsies 0 to 10 cm from the injection site. As expected, the highest venom concentrations were measured at the inoculation site (4.28 +/- 3.9 ng/4 mm). In addition, PMNs and MPO were detected up to 8 and 10 cm from the inoculation site, respectively. Neither PMNs nor MPO was detected in tissue absent of venom (kappa = 0.88, p < 0.001).

CONCLUSIONS

Loxosceles venom diffuses from the envenomation site. The extent of dermal inflammation mirrors the extent of Loxosceles venom diffusion. This observation implies that the venom itself defines the extent and magnitude of tissue injury following Loxosceles envenomation.

Intradermal anti-loxosceles Fab fragments attenuate dermonecrotic arachnidism

OBJECTIVE

Bites from the brown recluse spider and other arachnids from the genus Loxosceles frequently induce necrotic skin lesions that can be recalcitrant to treatment and disfiguring. The authors used a rabbit model of dermonecrotic arachnidism to address the therapeutic efficacy of intradermal (id) polyclonal anti-Loxosceles Fab fragments (alphaLoxd Fab) raised against Loxosceles deserta spider venom.

METHODS

Fab fragments were prepared by papain digestion and affinity chromatography from the IgG fraction of L. deserta antivenom raised in rabbits. Eighteen inbred New Zealand white rabbits were assigned to six groups of three. The rabbits received L. deserta venom (3 microg, id) injections into each flank. Cohorts of rabbits received single id injections (at one venom site/rabbit) of 30 microg alphaLoxd Fab at different times (T = 0, 1, 2, 4, 8, and 12 hours) after venom injection. In each rabbit the opposite flank was left untreated. As an additional control, one group of rabbits (T = 0) received nonspecific Fab (30 microg, id) in the opposite flank. Dermal lesions were quantified as a function of time through the use of a series of digital photographs and imaging software. In addition, myeloperoxidase (MPO) activity, a measure ofneutrophil accumulation, was determined in lesion biopsies. Lesion areas and MPO activities were analyzed by repeated-measures analysis of variance (ANOVA).

RESULTS

Lesion areas and MPO activity were markedly reduced when alphaLoxd Fab was administered very early after venom injections. As the interval between venom inoculation and antivenom treatment increased, the therapeutic benefit of alphaLoxd Fab decreased. The final time tested that demonstrated therapeutic efficacy of alphaLoxd Fab was T = 4 hours. Lesion attenuation was no longer apparent when alphaLoxd Fab was given 8 hours post inoculation.

CONCLUSIONS

Intradermal administration of alphaLoxd Fab attenuates Loxosceles-induced dermonecrotic lesion formation when given up to 4 hours after venom inoculation in this rabbit model.