Insect bites: causes and symptoms

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poison, allergens or other irritating metabolic components responsible for 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 ensure the correct management of the local skin reaction or emergency treatment for the allergic patient.

, the reaction generally results in the localized appearance of slight irritation and intense itching, which tend to resolve within a couple of days. This effect is typical in the case of bloodsucking insects: mosquitoes, horseflies, 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 only attack if provoked. Some of these species (bees, wasps, hornets and red ants) can cause painful stings and stimulate a severe allergic reaction (anaphylaxis) in patients at risk.

While not strictly belonging to the insect family, arachnids (spiders, mites and ticks) can also cause the same effect.

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

Insects that bite to feed Insects that bite to defend themselves Mosquitoes (Culex, Aedes, Anopheles)
Fleas (Siphonacteria)
Lice (Anopluri)
Pappataci (Diptera) Bees, wasps and hornets (Aculeated hymenoptera)

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

For further information: Electric mosquito nets and lamps: how to choose them generalized (itchy rash) and angioedema (swelling under the skin mainly affecting the face and lips).

When the swelling reaches the lower part of the throat it can obstruct the passage of air. Consequently, an edema of the glottis (swelling of the larynx at the level of the vocal cords) can occur, with difficulty in breathing, hoarse voice and cough.

In the most severe cases there may be a severe and persistent drop in pressure, loss of consciousness and anaphylactic shock.

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 of them can cause severe 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, does not have a body covered with hair and the abdomen is distinguished from the thorax by a thin peduncle. The females are provided with a long, smooth and straight sting, which communicates with a venom gland. They attack only. when they feel in danger, by injecting the venom. A wasp can inflict stings several times in a row, because it does not lose its injection system after being stung. 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 it does not lose during the attack.

• Unlike the 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, the malaria is caused by an organism (such protozoa Plasmodium), which spends part of its life cycle in mosquitoes, belonging, above all, to the genus Anopheles. Before the start of the meal, the hematophages inoculate a toxin which acts as a local anesthetic and which allows the insect to suck the blood of the victim without the victim noticing it, as well as preventing the blood from clotting. The characteristic itchy wheal that appears in the area of ​​the sting is the body's response to the saliva of these insects.

and are responsible for mild skin reactions that appear in most people after a sting, such as wheals, which are raised, red and itchy 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 sting, some allergens (such as the proteins present in the poison) can be conveyed, which are able to trigger various symptoms within a few minutes: in sensitive people a severe allergic reaction (anaphylaxis) can take place to insect venom. If the inoculation of the poison does not cause symptoms that are too intense, small first aid maneuvers can be implemented to limit the discomfort. If the reaction is more severe, it is advisable to seek immediate medical attention.

papular from insect bite). However, the saliva of these species contains anticoagulants and enzymes that can cause allergic reactions. The bite may appear as 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, midges and sand flies Any part of exposed skin.

Erythematous papule that can develop into a wheal, characterized by intense itching. If a person is particularly sensitive to insect bites, blisters (raised, large blisters filled with serous fluid) or bruising may develop.

Fleas They can be located in any area of ​​the body, but prefer bare feet and ankles.

Bumps or papules that are close together, itchy and centered by the puncture mark. They can lead to a papular urticaria or the formation of skin blisters.

Horseflies Any part of exposed skin

They cause very painful injuries. This manifestation can be associated with the appearance of hives, dizziness, weakness and angioedema (especially in the eyes and lips).Horseflies cut the skin with their jaws as they bite, instead of stinging it, which is why the marks can take a long time to heal and more easily cause infection.

Cimicidae (commonly called bed bugs) Any part of exposed skin (especially the face, neck, hands and arms).

Insect saliva causes intensely irritating, but generally not painful, wheals and skin rashes.

Arachnid stings Lice Pubic area or scalp.

The infested area is intensely itchy, with red marks at the puncture sites.

Ticks They bite any exposed skin.

Tick ​​bites aren't usually painful, but they can cause intensely itchy red marks that last longer than a week. In some cases they can cause swelling, blistering and bruising.

, hoarseness or difficulty in breathing;

Nausea, vomiting, or diarrhea;

Fast heart rate (tachycardia);

Dizziness or feeling faint

Difficulty swallowing (dysphagia);

Confusion, anxiety or agitation.

, fever and loss of consciousness. The toxic reaction constitutes a condition of medical emergency, as it can evolve rapidly and induce the typical signs of a poison intoxication (poisoning), with damage to muscle tissue (rhabdomyolysis), heart problems and kidney failure.

and / or bubbles.

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

, yellow fever, chikungunya and encephalitis, while the species Anopheles it can induce malaria and heartworm disease. Ticks are also vectors of many diseases, both in humans and animals: they can carry, for example, the causative agent that causes Lyme disease (the Borrelia burgdorferi).

Continued: Insect bites: management, treatment and prevention