Black Widow - Venomous Arachnids

Black Widow*

·              Widow (or hour-glass) spiders belong to the Latrodectus species of phylum Arthropoda.

Other Common Names

·              Hourglass Spider.

Species

·              Latrodectus mactans.

Physical Appearance

·               The widow spiders are cosmopolitan and are found all over the world, except regions with extremes of climate (polar regions, hot deserts, and high mountains). They are easily identified because they are the only spiders with a black, globose abdomen.

·               The female is much larger than the male with a leg span of 5 cm and body length of 1.5 cm. It has a characteristic red hourglass spot on the back of its shiny black body (Fig12.47). The male has more colourful white markings and isless aggressive than the female. In fact, the popular name “Black Widow” is due to the female’s practice of killing its partner after insemination.

·               The preferred habitats of these spiders include outdoor toilets, stables, barns, woodpiles, and dark crevices. They usually spin a somewhat irregular web in various corners of undisturbed areas of homes or the outdoors.

·              The red-back spider (Latrodectus hasselti) is best known from the adult female that usually has a black body and legs, with the following distinctive markings on the abdomen: the dorsal or top side has a distinct red stripe beginning in the mid portion, and on the underside is a red area in the shape of an hourglass or two triangles. However, variations on that pattern are common. The body may be light or dark brown; there may be red markings in front of and beside the main red band which may be light orange, or faded red. These spiders are found in open country areas, dark places, rubbish heaps, wood heaps, stacks of bags, or of scrap metal, under the bark of dead trees, empty tins, unused buckets, beneath or between stones, behind ferns, near gas or water metres, old boxes, etc.

Venom

·       The venom of black widow is neurotoxic, with six active components of molecular weight ranging from 5000– 130,000 D. The main component is alpha latrotoxin which binds avidly to a specific presynaptic receptor.

·       The venom affects the motor endplates of neuromuscular synaptic membranes by the binding of gangliosides and glycoproteins at the synapses. This causes the channels for sodium influx into neurons to remain open, as a result of which there is extensive release of acetylcholine and noradrenaline into the synapses, thereby inhibiting

·              reuptake. The end result is massive stimulation of motor endplates as the venom travels through the lymphatic system.

Clinical Features (Latrodectism )

Grade 1

1.    Sharp pain at bitesite, which may have one or two small puncture wounds, 1 to 2 mm apart. The immediate area may be warm, mildly indurated, and slightly reddened. Swelling of the affected part may occur after red-back spider bites.

2.  No systemic features.

Grade 2

1.  Muscular pain in bitten extremity.

2.  Extension of pain to the trunk.

3.  Local diaphoresis of bitten extremity.

4.  Tender regional lymphadenopathy may be present.

5. No systemic features.

Grade 3

·              Generalised muscle pain and weakness, with difficulty in walking.

·              Generalised sweating.

·              Tachycardia and hypertension are quite common.

·              ECG changes have been reported in a few victims: slur-ring of the QRS with ST and T segments depression, prolonged QT interval, and changes consistent with inferolateral ischaemia.

·              Leucocytosis is a common finding.

·              Nausea, vomiting, and headache are also very common.

·              Priapism, urinary retention, pyuria, proteinuria, microscopic haematuria, and testicular pain have been reported in a few cases.

·              During this period the victim often displays a contorted, grimacing, sweating facial appearance, referred to as “facies latrodectismica”.

·              In severe cases, the following manifestations occur: ptosis, salivation, hyperreflexia, tremor, convulsions, tachypnoea, and respiratory compromise. Board-like rigidity of the abdomen, shoulders, and back may develop. Although uncommon, acute renal failure has been reported following envenomation. Death is uncommon, but is more likely in the case of infants, old individuals, pregnant women, and chronic inva-lids.

Diagnosis

·              Leucocytosis

·              Elevated creatine kinase

·              Albuminuria.

Treatment

·              Calcium gluconate IV (10 ml of 10%) has been traditionally advocated for pain relief, but its actual efficacy is doubtful.

·              Pain is usually better controlled with a combination of IV morphine or pethidine and benzodiazepines (diazepam or lorazepam). Milder cases may be treated with aspirin, paracetamol, and/or codeine.

·              Application of cold or warm compresses (as guided by patient comfort) to bitten site is usually helpful.

·              Swelling responds to non-steroidal anti-inflammatory drugs.

·              Muscle relaxants such as diazepam, methocarbamol, or dantrolene may help relieve muscle spasm.

·              Tetanus prophylaxis is essential.

·              Wound care:

o     Cleansing with antiseptics.

o     Immobilisation, elevation, and serial observation.

o     If infection sets in, antibiotics must be administered.

o     Surgical intervention (excision) may be necessary if lesion exceeds 4 cm at 12 hours post-envenomation.