Cytotoxic venom effects the tissue that is destroyed around the bite and considerable tissue damage can ensue. Lesions of up to 10 cm in diameter may develop. The symptoms develop gradually and often the person is unaware that he has been bitten until the area around the bite becomes painful. It is therefore usually difficult to ascertain the spider species that has delivered the bite, particularly since it often takes place at night. In Southern Africa three genera are of particular medical importance.
Spider Research Centre
Two genera, Cheiracanthium and Loxosceles
produce cytotoxic venom and are medically important in Southern Africa. The
venom of a third genus Sicarius, found mainly in the drier regions, has a
combination of cytotoxic and haemotoxic components. However no proven cases of
human envenomation are known in South Africa and clinical evidence is
six-eyed crab spiders
Violin spiders usually live in grassland and in caves with only one species introduced into houses on the Witwatersrand. Violin spiders are nocturnal and at night may find their way into, for example, clothing, beds and shoes. To date no antivenom has been produced, and although no death has been reported in Southern Africa, plastic surgery is sometimes necessary to repair tissue damage. Violin spiders are usually brown or reddish brown in colour, with dark markings on their bodies. They have characteristic violin-shaped markings on the cephalothorax and are quite often confused with daddy-long-legs, which are not venomous.
SYMPTOMS AND SIGNS OF VIOLIN SPIDER BITES
The superficial bite is painless and initially goes unnoticed. About 2 hours after the bite a red swollen lesion, sometimes with a purple centre develops. Over the next day or two bleeding into the site causes a blackened lesion. By day 4 the swelling and inflammation subside, while cutaneous necrosis continues to spread slowly. Necrotic tissue sloughs off leaving a deep ulcerating wound which is slow to heal and leaves a nasty scar.
Treatment should focus on preventing and treating secondary infection using local antiseptics and systemic antibiotics to promote healing. Ulcers are managed conservatively through cleaning and dressing. Timely surgical cleaning may arrest a rapidly spreading lesion. Dapsone treatment in low doses for 14 days may control extension of the ulceration. Disfiguring scars may require reconstructive surgery with skin grafting at a later stage. The patient should receive a tetanus toxoid booster.
Sac spiders are commonly found outdoors and only one species
C. furculatum is regularly found in houses. There they may spend the
day in, for example, folds of curtains, bedding and clothing on a clothesline in
a soft silk sac-like retreat. Sac spiders are readily recognized by their pale
colour (fawn, yellow to yellowish green). A salient feature is the arrangement
of the legs, two pairs directed forwards and two pairs backwards with the first
pair being much longer than the others are. The tips of the legs and the
mouthparts are usually darkly coloured.
Medical records indicate that most patients were bitten when they were asleep. The bite is painless and the person is usually not aware that he has been bitten. Sometimes two fang bite marks (4-8 mm) apart are visible. A typical bull’s eye lesion may form with the surrounding area gradually becomes red, swollen and painful. The centre of the wound undergoes necrotic changes, leaving an ulcerating wound. The severity of the lesion is variable and local tissue damage and necrosis may be minimal or extensive. Systemic symptoms like tender lymph nodes, a rash, low-grade fever, headache, muscle and joint pain may occasionally develop.
The majority of the bites are self-limiting and heals spontaneously. Treatment of the bites should be directed to prevent and treat secondary infection using local antiseptics and systemic antibiotics. Occasionally an infected wound may develop into a rapidly spreading cellulitus, which requires aggressive antibiotic therapy. The patient should receive a tetanus toxoid booster.
The six-eyed crab spider is a sand-living spider and all the species are found only in the more arid regions of Southern Africa. They are brown spiders frequently covered with sand particles that adhere to their body. They have a crab-like appearance. The venom of this spider has only been tested on animals and studies on rabbits indicate that the venom may cause massive local tissue destruction and that serious internal hemorrhage may develop.