Loxoscelism

The clinical syndrome called loxoscelism is caused by the bite of Loxosceies species known as fiddle-back, brown recluse, or violin spiders. It is also called necrotic arach-nidism because of cytolytic components of the venom which cause necrosis of tissues around the bite wound. The common names of these spiders refer to a usually distinct fiddle- or violin-shaped marking on the dorsum of the cephalothorax, the neck of which is directed posteriorly. The base of the "violin" encompasses the eyes and is darkly contrasted against the lighter, general body color (Fig, 22.12). The eyes are distinctive among spiders in that there are only six, rather than the usual eight, and in that they are arranged in three groups of two eyes each (Fig, 22,12). The combination of a violin-shaped marking and this eye pattern distinguishes Loxosceies from all other spider genera. The body color and legs are usually a light, tawny brown but may be dark brown or even grayish in some populations. Loxosceies species quite closely resemble one another, usually requiring a specialist to make species determinations. The legs are relatively long and slender, making them agile spiders which can move quickly. They are primarily nocturnal hunters, either catching prey that comes into contact with their irregular webs or actively wandering from the security of

Arizona Spiders
FIGURE 22.12 Brown recluse spider, Loxosceles reclusa (Sicariidae), female, dorsal view. Note the dark, violin-shaped marking on the cephalothorax and arrangement of the six eyes in three groups of two eyes each. (Photo by G. R. Mullen.)

their silken retreats to capture food items. They do not wrap their prey but rely on their potent venom to quickly subdue it.

Approximately 70 species of Loxosceles have been described, with nearly 50 of them being found in the Americas (Gertsch and Ennik, 1983). The other species occur primarily in Europe and Africa. Fourteen Loxosceles species are found in the United States, including L, arizonica (Arizona, New Mexico, Texas), L. blanda (New Mexico), L. deserta (California), L. devta (Texas), L. laeta (Massachusetts, California), L. reclusa(southeastern except Florida, south-central, and midwestern states), L. rufescens (scattered localities in eastern states), and L. unicolor (southwestern states). L. laeta and L. rufescens are introduced species from South America and the Mediterranean region, respectively. L. rufescens is the most widely distributed member of the genus. It is endemic in southern Europe and northern Africa, from which it has spread to northern Europe and parts of the Middle East and has been introduced to Australia, Japan, Madagascar, and North America. The most important species are L. reclusa in North America, L. laeta in South America, and L. rufescens in the Mediterranean. These species have been introduced into nonnative areas through commerce and vacation travel.

Brown recluse spider (Loxosceles reclusa)

The brown recluse spider (Figs. 22.12 and 22.13) occurs primarily in the southeastern and central United States. Records outside this area are believed to represent scattered but not well-established populations, unlike L. rufescens. It is typically found indoors in warm, dry, undisturbed areas such as closets, attics, basements, storage areas, utility rooms, heated garages, lofts of feed mills, storerooms of broiler houses, and

FIGURE 22.13 Brown recluse spider, Loxosceks rtdusa. (Sicariidac), female. This spider is typically brown or tawny in color, with relatively long legs. (Photo by Sturgis McKeever.)

heated warehouses. It also is found hiding in cabinets and furniture, behind baseboards, door facings, and wall hangings, and in crevices and corners of rooms. Particularly common sites to find them are in old boxes and accumulations of materials that have not been disturbed for some time.

When mature, L, reclusa females are 7—12 mm in body length but may look much larger because of their long legs. The males are slightly smaller (mean, 8 mm) and are easily recognized by their bulbous pedipalps. Mating occurs from February to October but most commonly in June and July. The inseminated female produces 1—5 egg sacs, each containing 20—50 eggs. The egg sacs are white, about 17 mm in diameter, and flattened on the underside and convex above, and they are constructed in the spider's silken retreat. The spi-derlings usually emerge in 3—7 weeks and remain in the web with the female until after the first or second molt. Development is relatively slow, requiring 7—8 months under favorable conditions. During this time they molt another 6 or 7 times, undergoing 8 instars before becoming adults. Adults commonly live up to 2.5 years and have been known to survive 5—10 years under laboratory conditions.

The web of L. reclusa is constructed in poorly lighted, undisturbed, out-of-the-way places where the spider spends most of its time. It is a rather irregular, nondescript tangle of silken strands which continues to grow in thickness as new silk is laid down. Freshly deposited silk is sticky but soon becomes covered with dust, contributing to the unkempt appearance of the webbing. In addition to being a retreat, the silk serves to detect the presence of potential prey. When food is scarce, L. reclusa will leave the web at night to roam in evidence indicates acute injury to the blood vessels and infiltration by white blood cells at the site. Phospholi-pa-se, a major component of the venom, induces this white blood cell response while also causing platelets in the blood to aggregate and causing the liberation of inflammatory substances that contribute to development of the skin lesion.

The extent of tissue damage is largely dependent on the amount of venom injected at the time of the bite. Small doses can elicit very little response such that many bites go virtually unnoticed or do not result in ulcerations. A high dose, on the other hand, can result in destruction not only of the skin but also the underlying muscles into which the venom seeps due to gravity. The irregular shape of the skin lesion itself also reflects the effect of gravity, which is most evident in bites on the arms and legs. Some of the more severe cases result when the bite occurs in areas associated with fat tissue. The enzyme sphingomyelinase in the venom readily destroys lipid cells, causing saponification and extensive damage to the vasculature. This can cause severe tissue damage to the eyelids and face and to "baby fat" of infants.

Healing occurs very slowly, often requiring 6— 8 months or more. The edges of the wound become thickened and raised as the central area begins to undergo scar formation. The necrotic tissue gradually sloughs away, often exposing the underlying muscles. As the wound heals from beneath, a black scablike eschar develops over the damaged area, protecting it during the healing process (Fig. 22.15). Throughout this period it is important to keep the wound clean to avoid infections, which can significantly prolong the healing

FIGURE 22,15 Severe case of envenomation by brown recluse spider, Loxosceles reclusa., on inner surface of leg of 19-year-old woman. The bite occurred at night while she was sleeping in bed. The large, black eschar denotes extent of tissue damage, as evident 3 months after the bite, when picture was taken. (Courtesy of Carolyn Grissom, Shelbyville, TN.)

search of prey. It is under such circumstances that they are most likely to come in contact with humans.

Although being nonaggressive and very retiring, as its common name implies, the brown recluse spider will bite if provoked. Most encounters occur either at night, when a person rolls onto one of them in bed, or when a person puts on clothes or footwear into which the spider has crawled. Often the victim is not aware of the bite until 2—3 hr later, whereas in other cases it may be immediately felt as a stinging sensation. This is usually followed by intense local pain with the formation of a small blister at the bite site. The area around the bite becomes reddened and swollen as the venom seeps into the surrounding tissues, making it very sensitive to touch. The extent of the skin area involved is usually evident within 6—12 hr. The venom is highly cytotoxic, killing any cells it contacts. Within 24 hr the involved skin tissue turns dusky or purplish as the blood supply and oxygen to the affected area are cut off. The result is necrosis of the tissues and formation of a craterlike ulcer (Fig. 22.14) within 3-4 days. Histological

Loxocelism

FIGURE 22.14 Skin lesions on human hand and ankle caused by bites ofbrown recluse spider, Loxoscdtsrulusa(Sicariidae). Note the irregular shape of the damaged skin and formation of characteristic eschars, black scablike tissue that forms over the slowly healing bite wound. (From Honig, 1983, with permission of Harcourt Health Communications, Philadelphia.)

FIGURE 22.14 Skin lesions on human hand and ankle caused by bites ofbrown recluse spider, Loxoscdtsrulusa(Sicariidae). Note the irregular shape of the damaged skin and formation of characteristic eschars, black scablike tissue that forms over the slowly healing bite wound. (From Honig, 1983, with permission of Harcourt Health Communications, Philadelphia.)

FIGURE 22,15 Severe case of envenomation by brown recluse spider, Loxosceles reclusa., on inner surface of leg of 19-year-old woman. The bite occurred at night while she was sleeping in bed. The large, black eschar denotes extent of tissue damage, as evident 3 months after the bite, when picture was taken. (Courtesy of Carolyn Grissom, Shelbyville, TN.)

time. The end result is typically a sunken scar varying in size from about 2 cm up to 10 cm or more.

A small percentage of victims of brown recluse spider bites experience systemic reactions, usually within 24— 48 hr after envenomation. These may include fever, malaise, nausea, vomiting, joint pains, and a generalized pruritic rash. Occasionally the systemic symptoms can be even more serious in the form of hemolysis, intravascular coagulation, and renal failure.

Treatment of L. reclusa bite victims often entails administration of corticosteroids injected directly into the lesion; to be effective, however, this must be done within a few hours after the bite. If a limb is involved it should be elevated to help slow the spread of the venom by gravity. Other recommendations include cleansing the wound with hydrogen peroxide, applying hyperbaric oxygen to the ulcer, and using burn creams to alleviate pain. An alternative approach is early surgical excision of the affected skin in an effort to remove the venom before it can do further damage. Many physicians, however, are reluctant to do this because most bites are not destructive enough to warrant it. Others believe this to be a good approach, feeling that it is best to avoid the risk of disfiguring scars and subsequent skin grafts and other reconstructive surgery to repair more extensive tissue damage that could result. In cases of systemic reactions, the anticoagulant heparin can be administered to reduce the threat of intravascular coagulation. Aggressive therapy to counter hemolysis and the use of dialysis in cases of renal failure also may be required. Antivenins are available for treatment of L. laeta and other Loxosceies species in South America; however, despite the development of antivenin for treatment of L. reclusa bites in North America, its production has not proved to be commercially feasible.

Diagnosis of a brown recluse spider bite often can be difficult. Frequently the spider is not seen, or, if it is, it is not recovered for identification. In other cases the reaction is confused with fire ant stings, bee and wasp stings, assassin-bug or bed-bug bites, tick bites, skin abscesses and infections, slow-healing wounds of diabetic patients, pyodermic gangrenosa associated with rheumatoid arthritis patients, and various allergic responses. This is further compounded by the tendency of physicians and the general public to blame "bites" of unknown origin on spiders. Although some diagnostic tests have been developed, none of them have proved to be reliable for clinical use.

South American violin spider (Loxosceies laeta)

L. laeta is the largest species in the genus and poses a significant health concern in Central America and South America. It closely resembles L. reclusa, from which it is generally distinguished by its more reddish coloration and by the fourth pair of legs of the female being longer than the others. In addition to its common names of South American violin or brown recluse spider, it is called arafiade los rincones, or the corner spider, because of its occurrence indoors in the corners of rooms. This spider has been introduced to several parts of North America and Europe, where local populations have become established as far north as New England (United States) and Finland. In 1960 an infestation was discovered on the Harvard University campus at Cambridge, Massachusetts (USA), where it was believed to have been present for some 20 years. Established populations of L. laeta have been documented at several locations in southern California, where they also have been known to occur since the 1960s. At more northern locales, they tend to occur exclusively indoors, whereas in southern California they occasionally can be found in sheltered places outdoors.

Females produce multiple egg sacs, each containing about 50 eggs, which are deposited in a dense, cottony part of the web, usually at floor level. The number of egg sacs per female varies significantly and may be as high as 15 under laboratory conditions. In natural settings, females produce an average of 3—7 egg sacs following a single mating. Most eggs are produced during the spring and summer (October—January) in South America. The developmental time from egg hatch to adult ranges from as short as 6—8 months to a year or more. The adults are relatively long-lived, with mated and unmated females surviving about 3 and 4 years, respectively. Males live only about half as long as the females. Like other Loxosceies species, both sexes of L. laeta are able to survive prolonged periods without food and water, reportedly up to 2 years for some females. L. laeta often produces extensive webbing that is particularly noticeable in corners of rooms and along floor-level runways that they follow at the base of wails. These are composed of multiple layers of coarse silk, the amount of which reflects the degree of spider activity and duration of the infestation.

For many years before the cause was determined in 1947, skin lesions resulting from the bite of L. laeta in South America were known as gangrenous spot syndrome. The bite reaction is similar to that of L. reclusa, producing a necrotic lesion that heals slowly. However, it is more often accompanied by systemic effects that can be life-threatening. Such cases are referred to as viscerocutaneous loxoscelism, in which the lungs, kidneys, liver, and central nervous system may be damaged. The venom causes severe inflammatory, cytotoxic, necrotic, and degenerative changes in tissues, leading to fever, jaundice, blood or hemoglobin in the urine, and sensorial involvement. Recovery from severe cases of viscerocutaneous loxoscelism results in immunity to subsequent envenomation by this spider.

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