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Written by Dr Charlie Easmon, specialist adviser in travel medicine
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Where can snakes be found?
Snakes are to be found in most parts of the world, but only
around 15 per cent of the 3000 or so different types of poisonous snakes that
exist are regarded as posing a potential risk to humans. Most of these are to
be found in:
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| Only 15 per cent of snake species are considered to be
dangerous. |
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tropical and subtropical regions
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across most of the United States (except Alaska, Maine and
Hawaii)
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Australia.
Despite the many stories about constrictors, particularly
anacondas in the Amazon and pythons in the East, which are said to have
strangled adult humans, these need to be treated with a great deal of
scepticism. In practice it is only the poisonous snakes that are of interest.
How do you avoid snake bites?
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Wear long boots and trousers (which in rainforests also provide
some protection against leeches).
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Make a noise (or to be more correct vibrations in the
surroundings - snakes are deaf, but react to 'shaking'). Beat and
bash with a long branch or twig in the area three to five paces ahead, and
stand still for a short time before taking the next step. By far the majority
of snakes prefer to flee if given the chance. An exception is the
uncontrollably aggressive Australian Taipan, which also strikes out
unpredictably. Puff adders are very quiet but dangerous snakes, if you see one
sneak way with as little noise as possible.
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Avoid going out in a snake area in darkness. If it is necessary
to do so, then take a strong torch with you. Snakes prefer to evade bright
light and vibrations.
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If you see a snake, you should stand completely still. It will
instinctively prefer to go away and most snakes predominantly attack moving
targets.
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Do not put your hands down into holes, dark cavities or cracks
in rock, even if something has fallen down it. To reclaim anything, you can
attempt to fish it out with a stick, standing well away from the hole.
Creepy-crawlies other than snakes (for example scorpions) may also be
poisonous, and they are all lightning fast.
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The best possible advice is not to touch a snake in the wild.
The worse thing you can do is try to pick one up so that the doctor can
identify it! If you see a 'dead' snake, you should keep well clear.
Many people have been bitten two or three times by 'dead' snakes.
Only if someone has been bitten should you make sure that the snake is killed
and take it along for identification, but hold it by its tail and continue to
watch out for its head, or preferably put it in a sack that can be held away
from the body.
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All sea snakes (Hydrophiidae) are potentially extremely
poisonous and snorkellers and scuba divers should not attempt to inspect them
more closely. Sea snakes typically occur on the coasts of south-east Asia and
Australia.
Symptoms and danger signals
The risk of snake bites depends on many factors, such
as:
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the species and size of the snake.
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the amount of venom injected.
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the number of bites.
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the localisation of the bites (bites in the head or on the body
are most dangerous, but the bites will typically be on arms or
legs).
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the weight of the victim (most dangerous for
children).
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the general state of health of the victim.
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individual sensitivity to the venom.
Symptoms with rapid onset:
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local pain, swelling and discolouration at the site of the bite
are to be expected, but may not arise immediately after the bite (for example
the bite of the coral snake will rarely cause immediate local reactions), and
the general reactions often do not appear until 8 to 24 hours have
elapsed).
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within the first 10 to 15 minutes to a few hours after the bite
has occurred, general symptoms may appear such as a sense of anxiety, malaise,
vomiting, headache, dizziness, bouts of sweating, respiratory distress,
bleeding, heart failure and shock, muscle contractions, confusion, convulsions,
paralysis, unconsciousness and death.
Symptoms with later onset (often 6 to 24 hours after a
bite):
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local (around the site of the bite): increasing and massive
swelling of the whole arm, even if the bite wound is located right out on the
hand. Blistering and bleeding often occur in the skin and tissues just below
it, and muscles. Blood clots may occur in the surrounding blood vessels.
Necrosis (tissue death) of skin, connective tissue and muscles is an evident
risk.
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general symptoms: increasing grogginess, vomiting, respiratory
difficulties, fever, falling blood pressure and shock. Bleeding from the mucous
membranes (eg the gums), bloody vomit and stool and blood in the urine may also
occur. Disturbances of sensation or paralysis may occur, often first in the
face and later in the muscles involved in swallowing and breathing.
In principle, snake venoms act in three 'different'
ways:
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haemotoxins, ie venoms that split (haemolyse) the red blood
cells, or affect the ability of the blood to clot (coagulate).
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neurotoxins, ie venoms that in particular paralyse nerve
transmission to the muscles and in the worst case paralyse the muscles involved
in swallowing and breathing.
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cardiotoxins, ie venoms that have a direct harmful action on
the heart and lead to circulatory failure and shock.
But as a number of other factors, including possible allergic
reactions, are also involved in poisoning, the situation is often far more
complex and unclear, and there are often typically 'mixed' reactions
and symptoms.
First aid for snake bites
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Do not panic. Only a few poisonous snakes are really dangerous
to humans. In addition, often no venom will be injected with the bite. It is
estimated, for example, that venom is injected in only 20 to 30 per cent of
rattlesnake bites and in 50 per cent of bites from coral snakes.
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Avoid all unnecessary movement to prevent any venom from
spreading in the body.
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If possible, wash the site of the bite quickly and carefully
with clean (or boiled) water and soap.
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Spittle from Asian and African spitting cobras must be washed
away immediately from the eyes and mucous membranes to prevent it from being
absorbed into the body.
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A firm bandage (wide tourniquet) can be placed over and, if
necessary, around the site of the bite which may reduce the uptake and spread
of the venom, but it is important that a pulse can continue to be felt on the
'far' side of the bandage. However, in the United States this
treatment is not recommended for bites from pit vipers (for example
rattlesnakes), as the local tissue damage is regarded as posing more of a risk
than possible spread of the venom.
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It is important (as always) to keep the airways free of mucus,
vomit and blood.
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Ensure that the victim is transported as quickly as possible to
a doctor or hospital. The patient must be driven or carried, and if the person
is suffering from nausea and vomiting they should be made to sit up or be
placed in the 'recovery' position, ie lying on their side, to prevent
any vomit from going down into the airways and lungs. Many snake venoms act
quite slowly (4 to 20 hours after the bite), but this should not delay
transport, as other factors may also be involved (eg allergic people or
children in whom the venom may act more rapidly).
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There is often an urgent need for treatment with oxygen,
attachment to a drip and possibly anti-shock treatment.
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Antiserum treatment may be appropriate and life-saving, but
should always be overseen by a doctor.
Vaccinations
Snake venoms cannot be vaccinated against, but everyone,
particularly those who travel, should be sufficiently vaccinated against
tetanus and
diphtheria within the
last 10 years. Although constrictors are not poisonous, both their bites and
the bites of poisonous and non-poisonous snakes can cause infections, including
tetanus.
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Last updated 01.04.2005
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