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Overview
In North America, there are very few types of insects that carry venom or
poison and none whose venom is dangerous. It is possible, however, for an
insect bite or sting to cause an allergic reaction that can range from a mild
local reaction to something like a severe asthma attack. In extreme allergic
reactions, your airways can close up and you can even stop breathing.
The insect responsible for the largest number of severe allergic reactions
is the yellow jacket wasp. Considering both multiple stings and allergic
reactions to single stings, insects actually harm or even kill (in rare cases)
more than three times as many North Americans as snakes do.
Causes
Stinging insects:
- honeybees and bumblebees
- wasps (yellow jackets) and hornets
- fire ants (a wingless insect found only in the southeastern U.S.)
All three have different kinds of venom, but none is likely to be dangerous
in small doses unless someone is allergic to the poison.
Biting and bloodsucking insects:
- ticks
- flies (e.g., blackflies, sand flies, deerflies, horseflies)
- mosquitoes
- bedbugs
- fleas
None of them are actually poisonous, but some have saliva that can irritate
or provoke a reaction, and others can introduce infections when they bite.
Examples of infections and reactions include the following:
West Nile virus is passed on by the bite of mosquitoes that have become
infected by feeding on the blood of infected birds. The first confirmed Canadian
human case of West Nile virus was reported in Ontario in September 2002. Although
the risk of illness from West Nile virus is low for most Canadians, it is important
to recognize the symptoms and understand ways to reduce the risk of contracting
this disease. Please see the article on West Nile virus for more information.
Malaria, another serious infection transmitted by mosquitoes, is fortunately
uncommon in North America. Remember that travellers to areas where malaria is
common who get a fever after returning home should be seen promptly by their
physician. These travellers should be considered as having malaria unless proven
otherwise (with a blood test).
Lyme disease is caused by the bite of a deer tick that carries a parasite
capable of causing disease in humans. People who are infected with Lyme disease
may not experience symptoms right away after they are bitten. It is important
that people with Lyme disease be diagnosed in a timely manner, as most people
respond well to antibiotics.
Other ticks may cause a temporary spreading paralysis if they go undiscovered
for a few days. These creatures hang on and suck blood for as long as four
days, becoming fatter in the process. After about two days, some species start
producing new chemicals in their saliva, which can temporarily shut down parts
of the human nervous system. This is called tick paralysis, and it's quite different
from Lyme disease. It clears up after the tick is removed, but can be fatal
if breathing stops.
Mites that make their living around humans, such as house dust mites, don't
bite, but there are bird and animal mites that occasionally attack humans
and leave larvae (chiggers) in the skin. These cause local skin reactions in
both allergic and non-allergic people. Chiggers cause redness and itching, while
adult mites leave a small bite that usually becomes irritated hours or days
later. You're most likely to be bitten by a mite if you handle live birds or
poultry, pigs, rabbits, cats, dogs (especially puppies), seeds, straw, or hay.
Symptoms
Stinging insects
Bee and wasp stings are immediately obvious. A sharp pain is followed
by a burning sensation that soon resolves into a major itch. A red ring or bump
appears at the site of the sting. The important thing to remember is that bees'
stingers are barbed and usually remain in the skin. In its haste to get away,
the bee literally tears the stinger and the attached poison sac out of its abdomen,
killing itself in the process. Wasps and hornets lack barbs on their stingers
and can attack again and again.
The most serious immediate reactions occur from stings of the yellow-and-black
flying insects. A major allergic reaction that interferes with breathing
is called anaphylaxis or anaphylactic shock. Histamine, a chemical released
by the body during most allergic reactions, is released into the skin after
any insect bite and is responsible for the redness and itching. In anaphylaxis,
histamine causes major itching and redness of the skin (hives), and may also
be released in the airways, lungs, and other vital organs. It causes tissue
to swell, can close the airways (causing breathing to stop), and can drop blood
pressure to dangerously low levels.
Anaphylaxis can occur after a single bite, but this is rare. More typically,
fatal anaphylaxis occurs when somebody gets stung many times (50 to 100), still
nowhere near enough times to kill a non-allergic person.
It is possible to be killed by multiple stings. The insect most likely
to do this is the infamous Africanized killer bee, which has spread in recent
years from Mexico to parts of the southern United States. Contrary to popular
belief, this bee is no more poisonous than native varieties, but swarms are
highly aggressive and can inflict up to hundreds of stings in only a few seconds.
A human can tolerate about 10 wasp or bee stings per pound of body weight and
still survive, meaning it usually takes over 1000 stings to seriously harm a
healthy adult.
Biting and bloodsucking insects
Many people infected with West Nile virus will have only mild symptoms or
no symptoms at all. If symptoms do occur, they usually appear within 2 to
15 days. They may vary from flu-like symptoms that include fever, headache,
and body aches (in most people) to meningitis (inflammation of the lining
of the brain or spinal cord) or encephalitis (inflammation of the brain).
People with weaker immune systems, for instance people with cancer, diabetes,
or heart disease, are at much higher risk for the more serious symptoms of the
disease. Anyone experiencing signs of severe headache combined with high fever,
stiff neck, nausea, difficulty swallowing, vomiting, drowsiness, loss of consciousness,
lack of coordination, muscle weakness, or paralysis should receive emergency
medical attention.
Ticks cause no symptoms while they're biting. The only way to find
them is to examine your skin each night. Serious complications of tick bites
(Lyme disease and tick paralysis) normally only occur after the tick has been
attached for at least 24 hours. In tick-infested areas, a nightly check is a
good idea. For details about the symptoms of Lyme disease, please see the Lyme
disease article. The main symptom of tick paralysis is muscle weakness, poor
coordination, or paralysis spreading upwards (towards the head) from the site
of a tick bite or an attached tick.
Most people can guess at what's bitten them by looking at the site of the
wound or welt. Blackflies, for example, leave bites around the head, neck
and ears, while fleas often bite repeatedly around the feet and lower legs.
Bedbugs tend to leave lines of bites, usually on the torso. While their bites
can be extremely itchy, these insects don't cause serious diseases or reactions.
Treatment
With most bites and stings, the best treatment is to wait for the itching
to go away. Ice cubes, aspirin, antihistamines, and calamine lotion can
help. Application of an icepack to prevent the venom from spreading and application
of a paste of baking soda and water may also help to relieve welt formation.
If you are at risk of a major anaphylactic reaction (anyone who has had a severe
allergic reaction in the past is at risk), some doctors recommend carrying a
syringe filled with epinephrine.* This naturally occurring hormone will open
breathing tubes closed by anaphylaxis.
People who are allergic to insect stings may also undergo desensitization.
This is only useful for people who have tested positive in the skin-scratch
allergy test. By being exposed to small and harmless amounts of venom on a regular
basis for a few years, the body's response to the venom is changed, hopefully
lowering the risk of anaphylaxis from future stings to almost nothing.
Removing bee stingers usually requires a pair of tweezers. Some specialists
say that since the poison sac of a bee sting is still attached after the bee
is gone, care should be taken not to squeeze it, as this can force the remaining
poison into the wound. Others maintain that it doesn't matter how it is removed.
Either way, you should remove it as quickly as possible to minimize the poison
dose and the risk of infection.
You should also remove ticks with tweezers. They should be pulled straight
out, as this reduces the chance of the head and mouthparts remaining in the
wound. This may happen anyway. If it does, pluck out the easily accessible parts,
but don't fish around in the wound. These parts are unlikely to cause infection
and certainly won't transmit Lyme disease. Don't try to kill the tick with heat
or any chemical while it is still attached - just pull it out.
To avoid insects and insect bites, do not wear brightly coloured clothing
or strong, flowery perfumes. Do not carry overripe fruit or walk through clover
fields. People with allergies to stings should wear identification bracelets.
Applying insect repellents may also be useful to avoid insect bites. Wear long-sleeve
shirts, pants, and socks for protection.
*All medications have both common (generic) and brand names. The brand name
is what a specific manufacturer calls the product (e.g., Tylenol®).
The common name is the medical name for the medication (e.g., acetaminophen).
A medication may have many brand names, but only one common name. This article
lists medications by their common names. For more information on brand names,
speak with your doctor or pharmacist.
Other tips:
Tests are not normally required to diagnose bee stings and insect bites.
Diagnostic tests are only likely to be of use if someone finds a mite or tick
on their skin and wants to know if it's carrying anything dangerous. If a tick
is pulled out of the skin (see "Treatment and Prevention" for how
to properly do it), it should be checked for Borrelia burgdorferi, the
cause of Lyme disease, if the person was in an infested area.
Another diagnostic test that might bevaluable is an insect venom allergy test.
This involves scratching the skin with tiny doses of various insect venoms and
looking for the size of the hive that results to measure the allergic reaction
to the individual insect venom.
© MediResource Inc. Terms and conditions of use: The contents herein are for informational purposes only. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.