The adder (Vipera berus) is the only poisonous snake native to the UK. However, a number of dangerous snakes are kept as pets, and worldwide venomous snakes still cause significant mortality. There are three types of venomous snake:
1 Viperidae have long erectile fangs. They are subdivided into two types:
(a) Viperinae (true vipers, e.g. Russell’s viper [dabora], European adder), which are found in all parts of the world except America and the Asian Pacific.
(b) Crotalinae (pit-vipers, e.g. rattlesnakes, Malayan pit-viper), which are found in Asia and America. They have small heat-sensitive pits between the eyes and the nostrils. The venom of both of these classes of snake is vasculotoxic.
2 Elapidae (cobras, mambas, kraits, coral-snakes) are found in all parts of the world except Europe. They have short, unmoving fangs and the venom produces neurotoxic features. Venom from the Asian cobra and the African spitting cobra also produces local tissue necrosis.
3 Hydrophiidae (sea-snakes) are found in Asian Pacific coastal waters. They have short fangs and flattened tails. The venom is myotoxic.
Russell’s viper is the most important cause of snake-bite mortality in India, Pakistan and Burma. There is local swelling at the site of the bite, which may become massive. Local tissue necrosis may occur, particularly with cobra bites. Evidence of systemic involvement occurs within 30 min, including vomiting, evidence of shock and hypotension; haemorrhage due to incoaguable blood can be fatal.
There is not usually any swelling at the site of the bite, except with Asian cobras and the African spitting cobrahere the bite is painful and is followed by local tissue necrosis. Vomiting occurs first followed by shock and then neurological symptoms and muscle weakness, with paralysis of the respiratory muscles in severe cases. Cardiac muscle can also be involved.
Systemic features are muscle involvement, myalgia and myoglobinuria, which can lead to acute renal failure. Cardiac and respiratory paralysis may occur.
A firm pressure bandage should be placed over the bite and the limb immobilized. This greatly delays the spread of the venom. Arterial tourniquets should not be used and incision or excision of the bite area should not be performed. The type of snake should be identified if possible. In about 50% of cases no venom has been injected by the snake bite and antivenoms are not generally indicated (unless systemic effects are present) as they can cause severe allergic reactions. Nevertheless, careful observation for 12-24 hours is necessary and antivenom must always be given when indicated, as the mortality of snake bite is 10-15% with certain snakes. General supportive measures should be given as necessary, as for all poisoning. These include diazepam for anxiety and intravenous fluids with volume expanders for hypotension. Treatment of acute respiratory, cardiac and renal failure is instituted as necessary. Specific measures, i.e. antivenoms, can rapidly neutralize venom, but only if an amount in excess of the amount of venom is given. Antivenoms cannot reverse the effects of the venom so they must be given early. They do minimize some of the local effects and may prevent necrosis at the site of the bite. Antivenoms should be administered intravenously by slow infusion, the same dose being given to children and adults. Allergic reactions are frequent, and adrenaline (1 in 1000 solution) should be available. Antivenoms are usually rapidly effective. In severe cases the antivenom infusion should be continued even with allergic reactions, with subcutaneous injections of adrenaline being given as necessary. Large quantities of anti venom may be required. Some forms of neurotoxicity, such as those induced by the death adder, respond to anticholinesterase therapy with neostigmine and atropine. Local wounds often require little treatment. If necrosis is present, antibiotics should be given together with initially minimal surgical treatment. Skin grafting may be required later. Antitetanus prophylaxis must be given. Antivenoms must be kept readily available in all snakeinfested areas.
Scorpion stings are a serious problem in the tropics and cause 1000 deaths per year in Mexico. The poison glands are situated in the end of the tail. Severe pain occurs immediately at the site of puncture, followed by swelling. This should be treated by a firm pressure bandage to avoid the spread of the neurotoxic venom. Signs of systemic involvement include vomiting, respiratory depression and haemorrhage. Treatment is supportive. Antivenom is available in certain countries.
The black widow spider (Latrodectus mactans) is found in North America and the tropics and occasionally in Mediterranean countries. The bite quickly becomes painful and generalized muscle pain, sweating, headache and shock occur due to absorption of rapidly acting neurotoxins. No systemic treatment is required except in cases of severe systemic toxicity, when specific antivenom should be given where this is available. Intravenous calcium gluconate may help the muscle spasms.
Loxosceles causes many bites in Central and South America. L. reclusa, the brown recluse spider, is also found in the southern USA. Spiders are often found in bedrooms, so that patients are often bitten at night. There is a burning pain at the site of the bite, followed by a necrotic ulcer in some cases. Systemic effects, which include fever, vomiting and haemolysis, are rare. No treatment is indicated except in severe cases, when an anti venom should be given if available. Phoneutria nigriventer, the banana spider, and Atrax robustus, the Sydney funnel-web spider, can both give nasty bites, which are occasionally fatal.
Insect stings, e.g. from wasps and bees, and bites, e.g. from ants, produce pain and swelling at the puncture site. Death occurs (12 per year in the UK) and is usually due to anaphylaxis, which requires urgent treatment. Patients who have severe local reactions to stings or a mild anaphylactic reaction should carry a Medi-jet syringe for self-administration of adrenaline should a further sting occur. Desensitization can be carried out, but the course is prolonged and often needs to be repeated.
Marine animals There are many poisonous fish that can be dangerous. They are usually found in tropical waters but cases have
been described worldwide. Stringrays and scorpion fish are two examples that sting by injecting venom through barbed spines. There is immediate severe local pain and swelling, which may be followed by tissue necrosis. Systemic effects include diarrhoea, vomiting, hypotension, cardiac arrhythmias and convulsions. Treatment is supportive. Care should always be taken in waters where these fish are known to be present. Venomous Coelenterata include jellyfish, sea anemones and the Portuguese man-of-war. The tentacles contain toxin that, following a sting, produces painful wheals at the site of contact. These wheals may become necrotic. Rarely there are systemic side-effects, including abdominal pain, diarrhoea and vomiting, hypotension and convulsions. Treatment consists of removing the tentacles, having first applied acetic acid (vinegar) to them. Alcohol compounds should not be used.
Only the octopus and cone-shells are venomous to humans. The blue-ringed octopus, which is found in Australia, has saliva which contains the neurotoxin tetrodotoxin. This flows into the wounds from the beak of the octopus and can cause serious systemic effects. In cone-shells the venom is found in association with their radular teeth. A bite initially produces local numbness, which can then spread over the body and may even tually lead to paralysis.
This can occur with fish and shellfish. In some cases it is attributable to toxins, but most poisonings occur as a result of pathogens such as Salmonella or hepatitis A virus. Ichthyosarcotoxic fish contain toxins in their blood, skin and muscle and are the commonest cause of poisoning.
CIGUATERA. Poisoning occurs chiefly with the reefdwelling fish from around the Pacific and Caribbean. The fish contain ciguatoxins from the plankton Gambier discus. Most cases of poisoning are due to the red snapper, grouper, barracuda and amberjack fish but many other species may be responsible. The poisonous fish cannot be distinguished from identical fish that do not contain the poison. The toxin is unaffected by cooking. Symptoms occur from a few minutes to 30 hours after ingestion of the fish. They include numbness and paraesthesia of the lips, abdominal pain, nausea, vomiting and diarrhoea. Visual blurring, photophobia, metallic taste in the mouth, myositis and eventual hypotension and shock can also occur. Treatment is symptomatic, but symptoms can last for up to 2 weeks.
SCROMBOID FISH. Fish such as tuna, mackerel and skipjack contain a high degree of histidine. This is decarboxylated by bacteria to histamine and, particularly if the fish are allowed to spoil, large amounts can accumulate in the fish, producing flushing, burning, pruritus, headache, urticaria, nausea, vomiting and bronchospasm 2-3 hours after ingestion. Treatment is symptomatic; care should be taken only to eat fresh fish.
Tetrodotoxin-containing puffer-fish are found in both sea and freshwater areas of Asia, India and the Caribbean. Symptoms that follow ingestion are circumoral paraesthesia, malaise and hypotension, with more severe cases producing ataxia and neuromuscular paralysis. The mortality is 50-60%.
SHELLFISH. Bivalve molluscs, e.g. mussels, oysters, scallops and clams, can acquire the neurotoxin saxitoxin from the dinoflagellate Gonyaulax. These protozoa colour the sea red and molluscs should never be taken from such areas. Symptoms are similar to those caused by tetrodotoxin, but are usually less severe. Treatment is symptomatic.