Insect bites: causes and symptoms

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Generality

There are many species of arthropods (insects, arachnids and others) that regularly or occasionally bite or bite animals and humans, for a number of different reasons.

Insect bites are frequent especially in the summer period, but for many people the possible contact with these animals is a serious problem, with which to live for the whole life. Through the puncture, the insect can inject venom, allergens or other irritating metabolic components into the skin, causing pain, itching, redness, swelling and, in susceptible people, even severe allergic reactions. It is important to be able to distinguish the bites of the most common insects, in order to guarantee the correct management of the local skin reaction or the emergency treatment for the allergic patient.

Stings and bites

Insect bites are common and usually harmless.

Considering that an insect can sting to puncture the skin with the purpose of feeding on blood, the reaction, generally, results in the localized appearance of slight irritations and intense itching, which tend to resolve within a couple of days. This effect is typical in the case of bloodsucking insects : mosquitoes, horse flies, midges and fleas.

A sting can also be the result of a defense mechanism : insects can use their sting to inject toxic and poisonous substances, in order to protect their hives or nests. These insects usually attack only when provoked. Some of these species (bees, wasps, hornets and red ants) can cause painful bites and stimulate a severe allergic reaction (anaphylaxis) in patients at risk.

Although they do not belong strictly to the insect family, arachnids (spiders, mites and ticks) can also cause the same effect.

Finally, insects may be involved in the transmission of diseases, such as yellow fever and malaria, so interaction with these vectors can potentially make them vulnerable to more serious conditions.

Insects that sting for food

Insects that sting to defend themselves

Mosquitoes ( Culex, Aedes, Anopheles )

Fleas ( Sifonatteri )

Lice ( Anopluri )

Pappataci ( Diptera )

Bees, wasps and hornets ( Hymenoptera aculeati )

From the histo-morphological point of view, the appearance of an insect sting is generally characterized by a round and smooth cut of the skin, red or white, with an erythematous and itchy halo. This wheal can manifest itself with a perivascular infiltrate composed mainly of lymphocytes and some eosinophils. However, it should be pointed out that the appearance of the wheal is also common to other conditions, including: drug reactions, urticarial reactions, pre-vesicular onset of bullous pemphigoid, etc.

Symptoms and reactions

The severity of the puncture varies depending on the type of insect and the individual sensitivity of those who suffer this damage.

An insect bite can cause different reactions:

The normal reaction involves only the area around the puncture, with immediate pain, redness, swelling and itching, but is harmless in most cases. In general, the affected region remains sore and itchy for a few days.
A more extensive local reaction shows an area of swelling greater than 5 cm and with signs (redness and burning) that tend to worsen gradually in the first two days after the insect bite. This condition tends to resolve itself within 10 days.
Reactions of varying intensity can affect different parts of the body ( systemic or allergic ), such as generalized urticaria (rash with itching) and angioedema (subcutaneous swelling that mainly affects the face and lips).
When the swelling reaches the lower part of the throat it can hinder the passage of air. Consequently, edema of the glottis may occur (swelling of the larynx at the level of the vocal cords), with difficulty breathing, hoarse voice and cough.
In the most severe cases, severe and persistent pressure drops, unconsciousness and anaphylactic shock may occur .

Some insects are more likely to cause allergic or toxic reactions. Here are some examples:

Bees, wasps and hornets are members of the Hymenoptera order: they differ in the way they inflict a sting, but all can cause serious reactions in people susceptible to their allergens.

Bees are insects with a serrated sting, connected to a gland that contains poison: when they sting, they leave the sting inside the victim and with it also the last segments of the abdomen and part of the viscera. Thus mutilated, bees are generally destined to die.
The wasp, unlike bees, has no body covered with hair and the abdomen is distinct from the chest thanks to a thin peduncle. The females are provided with a long, smooth and straight spike, which communicates with a venom gland. They attack only when they feel in danger, injecting the poison. A wasp can inflict punctures several times in a row, because it does not lose its injection apparatus after the puncture. These insects can also attack in swarms.
The hornet is a large insect, similar to the common wasp and, as such, has a venom gland and sting, which does not lose during the attack.

Unlike Hymenoptera, mosquito bites do not generally cause important reactions, unless they act as "vectors" for particular pathogenic microorganisms (viruses, bacteria and parasites), which actually live inside these insects. For example, malaria is caused by an organism (protozoa of the genus Plasmodium ), which spends part of its life cycle in mosquitoes, belonging, above all, to the genus Anopheles . Before the start of the meal, the hematophagous inoculate a toxin that acts as a local anesthetic and that allows the insect to suck the victim's blood without her noticing it, as well as preventing blood from clotting. The characteristic itchy pimple that appears in the puncture area is the body's response to the saliva of these insects.

Insect poison

Insect venom belonging to the order of hymenoptera can cause allergies, since it contains toxic substances and components with allergenic activity. In Italy, the most widespread insects belonging to this category are bees, hornet wasps. Toxic substances produce a vasodilator effect and are responsible for mild skin reactions that appear in most people after a puncture, such as wheals, ie raised, itchy red spots associated with pain or burning in the injured area. The substances with allergenic activity, on the other hand, cause symptoms only in individuals predisposed to allergy . Through the puncture some allergens (such as the proteins present in the poison) can be conveyed, which are able to trigger different symptoms within a few minutes: in people sensitive to insect venom, a severe allergic reaction ( anaphylaxis ) can occur . If the inoculation of the poison does not cause too intense symptoms, to limit the discomforts can be implemented small first aid maneuvers. In the event that the reaction is more severe, it is advisable to request immediate medical intervention.

bloodsucking

Insects that sting to feed produce characteristic symptoms, depending on the eating habits of the responsible parasite and the chemical composition of the saliva. In most people, "non-poisonous" insect bites usually cause nothing more than intense itching and local irritation ( papular sting from an insect bite ). However, the saliva of these species contains anticoagulants and enzymes that can cause allergic reactions. The bite may look like a small raised red spot ( wheal ). Unfortunately the instinct to scratch the injured area usually results in an open wound, which can become infected and take longer to heal.

Type of insect	Favorite part of the body	Symptoms that may appear
Common insect bites
Mosquitoes, gnats and sand flies	Any part of exposed skin.	Erythematous papula that can develop into pompho, characterized by intense itching. If a person is particularly sensitive to insect bites, they can develop blisters (large vesicles full of serous fluid) or bruising.
Fleas	They can be located in any area of the body, but prefer ankles and bare feet.	Close-up wheals or papules, itchy and centered by the mark of the sting. They can induce papular urticaria or the formation of skin blisters.
Tafani	Any part of exposed skin	They cause very painful injuries. This manifestation may be associated with the appearance of hives, vertigo, weakness and angioedema (especially in the eyes and lips). Horseflies cut the skin with their jaws while they bite instead of stinging it: this is why the signs can take a long time to heal and more easily cause infection.
Cimicidae (commonly called bed bugs)	Any part of exposed skin (especially face, neck, hands and arms).	The saliva of the insect causes intensely irritating but generally painless rashes and rash.
Arachnid stings
Lice	Pubic area or scalp.	The infested area is intensely itchy, with red marks at the puncture sites.
Ticks	They bite any part of uncovered skin.	Tick bites are not usually painful, but can cause intensely itchy red marks that last more than a week. In some cases they can cause swelling, blisters and ecchymoses.

Complications

Insect bites can evolve severely if one or more of the following conditions develop:

A severe allergic reaction (anaphylaxis);
A toxic reaction;
An extended skin reaction;
An infection at the puncture site;

If you experience any of the following symptoms following an insect bite, it is essential to consult your doctor:

Dyspnea, hoarseness or difficulty breathing;
Nausea, vomiting or diarrhea;
Fast heart rate (tachycardia);
Dizziness or fainting sensation;
Difficulty in swallowing (dysphagia);
Confusion, anxiety or agitation.

Toxic reaction from multiple punctures

In the event that the insects (bees or wasps) are particularly aggressive, or if they are surrounded by a swarm, it is possible that the bites are multiple. If these exceed the dozen, the accumulation of poison can induce a toxic reaction, which is manifested by nausea, vomiting, dizziness, convulsions, fever and loss of consciousness. The toxic reaction is a medical emergency, as it can evolve rapidly and induce the typical signs of poison poisoning (poisoning), with damage to muscle tissue (rhabdomyolysis), heart problems and kidney failure.

Infected stings

At times, insect bites can be infected, particularly if you give in to instinct to repeatedly scratch the skin flap. This mechanism can damage the skin and allow bacteria to infect the injured area.

The presence of the following signs, locally, may indicate an infection:

Presence of pus in and around the wheal;
Increased redness, swelling and pain;
Appearance of vesicles and / or boils.

Over a period of several days, the infection can spread and can sometimes become severe.

Diseases transmitted by vector insects

In some parts of the world, insect bites can lead to more problematic complications, as insects are carriers or carriers of various diseases. For example, the sting of "tiger mosquitoes" (especially Aedes ) can transmit diseases such as dengue, yellow fever, chikungunya and encephalitis, while the Anopheles species can induce malaria and filariasis. Ticks are also vectors of many diseases, both of humans and animals: they can carry, for example, the etiological agent that causes Lyme disease ( Borrelia burgdorferi ).

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