Scorpion Stings

In many areas of the world, scorpion stings are medically much more important than snake bites. Such areas include Mexico, Trinidad, parts of Brazil, North Africa, the Middle East, and India. A 1979 survey in Libya revealed an estimated yearly total of over 6500 scorpion stings in a population of 3 million people, with at least 50 deaths, most of which were in children under 2 years old. In Mexico there are an estimated 300 000 cases a year, with about 1000 deaths (WHO, 1981). The extent of the problem in some areas is also increasing; for example, in Minas Gerais State in Brazil, scorpions such as Tityus serrulatus are rapidly colonising urban areas.

Scorpions have four pairs of legs, a pair of claws, a body with a broader front part and a six-jointed tail-like abdomen. The terminal segment of the 'tail' is called the telson (Figure 21.9) and contains two venom glands connecting with the curved, needle-sharp sting which is used either in defence or in obtaining food. The tail with its sting is always brought forward in front of the scorpion. Scorpions never sting backwards and this feature enables safe handling of scorpions (provided one is familiar with their habits). The length of adult scorpions varies from under 2 cm up to about 25 cm, but the length of the scorpion does not relate to its danger to humans.

Most scorpions are nocturnal, and feed on spiders and insects. During the daytime, they hide under stones, in cracks, among debris or in clothing; desert species often burrow, sometimes to a depth of as much as 2.5 m. Scorpions are divided into six families and all the dangerous ones are in the Buthidae family. Probably the five species most dangerous to humans are Centruroides (southern United States, Central America), Tityus (South America), Androctonus (Africa), Leiurus (Africa and Middle East), and Buthus (Africa, Middle East, Asia).

Figure 21.9 Scorpion, with young, showing the terminal segment or telson, which contains two venom glands. The sting is always brought forward over the abdomen

Avoiding Scorpion Sting

The traveller in areas where scorpions are common can take certain simple precautions to avoid being stung:

• Shoes should be worn when walking in the dark.

• Clothes, socks and footwear should be checked carefully for scorpions by shaking them in the morning before dressing.

• A torch should be used when searching in dark areas such as cupboards.

• Storing domestic rubbish near the house should be avoided.

• Travellers, especially children, should be actively discouraged from handling scorpions.

Clinical Features

These are partly dependent on the amount of venom injected relative to the weight of the victim. Pain around the bite site is the commonest feature; this can be severe and last for several hours, even 1-2 days. Local erythema and swelling are unusual, but itching and paraesthesia may be prominent and last for many days. Only a small proportion of victims develop systemic envenoming; this is more common in children and may occur within several minutes of the bite in severe cases. Symptoms and signs are caused primarily by activation of the autonomic nervous system by venom components, leading to an 'autonomic storm' (Table 21.7).

In severe envenoming, the cardiovascular manifestations of severe hypertension, acute pulmonary oedema and myocardial failure are particularly prominant. Respiratory failure may also occur, due to pulmonary oedema, bronchial hypersecretion and paralysis of respiratory muscles. Both tachycardias and bradycardias are common. Acute pancreatitis has been reported to occur in Tityus stings and, in India, necropsy evidence of intravascular coagulation has been reported in Buthus stings.

Table 21.7 Major signs and symptoms of scorpion envenoming

Tachypnoea

Excessive salivation

Nausea and vomiting

Lacrimation

Sweating

Abdominal pain

Muscle twitches and spasms

Hypertension

Pulmonary oedema

Cardiac arrhythmias

Hypotension

Respiratory failure

Treatment

First aid consists of reassuring the victim, immobilising the limb and getting the victim to hospital. If local pain is severe, the area should be infiltrated through the puncture wound with 2-5 ml 1% lidocaine (lignocaine) hydro-chloride. Alternatively, opiates may be used, but care must be taken not to cause respiratory depression. Local injection of emetine hydrochloride has been used to control pain, but is not generally recommended because it sometimes causes local necrosis. Specific scorpion anti-venom is available in many parts of the tropics, although supplies are variable. It is indicated, especially in children, for systemic envenoming (ideally, by intravenous infusion as in snake bite, but intramuscular administration may be effective). When antivenom is not available, supportive treatment is indicated. Prazosin appears to be effective in treating hypertension and cardiac failure; it may block the action of scorpion venom peripherally. Nifedipine has also been used to manage hypertension; opinion is divided on its efficacy and it should probably only be used in combination with prazosin. Pulmonary oedema should be treated by conventional means; intravenous vasodilators, such as sodium nitroprusside, may be needed in severe cases. Subcutaneous atropine and intravenous calcium gluconate have been advocated to alleviate systemic symptoms, but evidence of their efficacy is lacking and they could theoretically be harmful.

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