Envenomation by a spider, Agelenopsis aperta (family: Agelenidae) previously considered harmless

[Indirect and mixed mechanisms of action in toxic myopathies]

Toxic myopathies are a group of pathologies characterized by a structural and/or functional disturbance of muscles induced by an exogenous agent. The most frequent are those induced by drugs used in clinical practice. Illegal drugs, pesticides, solvents, metals and even physical and gaseous agents can cause this kind of disease and exert toxicity on muscle tissues. Some toxins from animals, plants or micro-organisms are potent myotoxic agents, which can lead to fatal complications. Respiratory arrest and rhabdomyolysis are often referred to as the ultimate complications of these pathologies. Several mechanisms of action can be triggered. Muscles may represent a direct target for exogenous agents by acting on the myocyte components or indirect target by inducing functional disorders. These disorders are triggered by neuromuscular interferences (organophosphates, antipsychotics, curares, etc.) and endocrine (glucocorticoids and ethyl alcohol), immune (d-penicillamine and statins) and hydroelectrolytic system dysfunctions (diuretics, laxatives and toluene). Direct and indirect effects can be induced by the same toxic agent, such as carbon monoxide, glucocorticoids, ethyl alcohol and some toxins from snake venoms.

Spider envenomation in North America

In North America, spider envenomation is perceived to be a greater threat than in actuality; however, it still is a valid source of morbidity and, very rarely, mortality. Only 2 groups (widows, recluses) are medically important on this continent. Widow bites affect the neuromuscular junction, have minor dermatologic expression, and are treated with analgesics and antivenom. Recluse bites vary from mild, self-limiting rashes to extensive dermonecrosis. Recent awareness of methicillin-resistant Staphylococcus aureus as a ubiquitous cause of skin injury that is often mistaken as attributable to recluse bites has questioned the credence of spiders being the cause of idiopathic wounds.

Arachnids misidentified as brown recluse spiders by medical personnel and other authorities in North America

Misidentification of harmless or nearly benign arachnids as Loxosceles spiders by medical personnel and other authorities proliferates misinformation in regard to alleged loxoscelism and leads to decreased health care. This is especially true in areas of North America where Loxosceles spiders are rare or non-existent. A diverse assemblage of such misidentified arachnids is presented here. It is hoped that authorities will honestly assess their arachnological limitations and, instead, seek qualified arachnologists for spider identifications.

Medical aspects of spider bites

Spiders have been incriminated as causes of human suffering for centuries, but few species worldwide cause medically significant envenomation. Widow spiders (Latrodectus spp.) occur worldwide and cause latrodectism, which is characterized by pain (local and generalized) associated with nonspecific systemic effects, diaphoresis, and less commonly other autonomic and neurological effects. Recluse spiders (Loxosceles spp.) are distributed mostly through the tropical and subtropical Western Hemisphere and can cause severe skin lesions and rarely systemic effects; most bites are unremarkable. Highly dangerous spiders in South America (armed spiders) and Australia (funnel-web spiders) cause rare but severe envenomation requiring medical intervention and sometimes antivenom. Most other spiders involved in verified bites cause minor, transient effects. Many spiders blamed for causing medical mischief have been elevated to medical significance via circumstantial evidence, poor reporting, and repetitive citation in the literature; several species have been shown to be harmless with more stringent scientific evidence involving verified bites in humans.

Diagnosis of loxoscelism in a child confirmed with an enzyme-linked immunosorbent assay and noninvasive tissue sampling

BACKGROUND

Confirmation of mild bites caused by Loxosceles reclusa with swab testing has not been previously documented, to our knowledge.

METHODS

We report a case using an enzyme-linked immunosorbent assay (ELISA) test.

RESULTS

A lesion lacking necrosis or other specific signs of loxoscelism was confirmed by identification of the Loxosceles venom and further confirmed by identification of a spider found in the patient's bed.

LIMITATIONS

This is a pilot single-case report for this enzyme-linked immunosorbent assay test.

CONCLUSIONS

A sensitive and specific enzyme-linked immunosorbent assay designed to detect Loxosceles venom, using a specimen obtained by swabbing the lesion, can aid in diagnosis of loxoscelism.

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.

Arachnid envenomation

This article focuses on the medically relevant arachnid species found in North America and selected other arachnids from around the world. While it is largely still true that the geographic location of the envenomation assists in determining the species responsible, the booming trade in arachnids as exotic pets should prompt the clinician to inquire into this possibility. Expert advice should be sought in either case; species identification is critical in determining the need for and proper type of antivenom therapy.

Diagnoses of brown recluse spider bites (loxoscelism) greatly outnumber actual verifications of the spider in four western American states

We attempt to demonstrate that physicians overdiagnose loxoscelism (colloquially known as 'brown recluse spider bites') by comparing the numbers of such diagnoses to the historically known numbers of Loxosceles spiders from the same areas in four western American states. The medical community from non-endemic Loxosceles areas often makes loxoscelism diagnoses solely on the basis of dermonecrotic lesions where Loxosceles spiders are rare or non-existent. If these diagnoses were correct then Loxosceles populations should be evident, specimens should readily be collected over the years and there should be a reasonable correlation between diagnoses and spider specimens. In 41 months of data collection, we were informed of 216 loxoscelism diagnoses from California, Oregon, Washington and Colorado. In contrast, from these four states, we can only find historical evidence of 35 brown recluse or Mediterranean recluse spiders. There is no consistency between localities of known Loxosceles populations and loxoscelism diagnoses. There are many conditions of diverse etiology that manifest in dermonecrosis. In the western United States, physician familiarity with these conditions will lead to more accurate diagnoses and subsequent proper remedy.

Reports of presumptive brown recluse spider bites reinforce improbable diagnosis in regions of North America where the spider is not endemic

Envenomations by the brown recluse spider have been reported throughout North America, despite the fact that the spider's range is limited to the South and central Midwest of the United States. Several of these medical reports have originated from regions of nonendemicity where the spider has never or rarely been documented and brown recluse spider populations are unknown. In most of these reports, no spider is positively identified in association with the dermonecrotic wound, and diagnosis has been based on clinical examination findings. Considering the extreme rarity of brown recluse spiders in areas of nonendemicity, the diagnosis of a presumptive bite is a misdiagnosis that reinforces the assumption that brown recluse spiders are common local etiologic agents of necrosis. There are many medical conditions of diverse origin that have been misdiagnosed as brown recluse spider bites, some of which can be fatal or debilitating. Physicians' awareness of these conditions will increase diagnostic accuracy in areas of North America where bites from brown recluse spiders are improbable.

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.