In some sensitive individuals, insects can cause adverse reactions which can be severe and considerably alter their quality of life. These reactions can be allergic or non-allergic. Non-allergic reactions (venom reaction) appear 24-48 hours after the sting and manifest as painful local inflammation, less than 10 cm. Allergic reactions can be local or systemic, and although a considerable percentage of the population can present an allergic reaction after a sting, only a small proportion will suffer a serious generalized, life-threatening condition. Dr. Manuel de Barrio Fernández, Allergist and Insect Sting Expert, explains which insects produce the most cases of allergy, as well as the main symptoms and treatments to be applied.
How does an allergic reaction to insects manifest itself?
Local allergic reactions manifest with swelling (greater than 10 cm), itching and pain in the sting area; they are uncomfortable but not serious. In these patients, new stings may produce more intense but rarely generalized reactions. In systemic stings, symptoms are manifested throughout the body and may be cutaneous (urticaria-angioedema) or may be associated with other symptoms such as coughing, respiratory distress, nausea, vomiting, urinary incontinence, dizziness, collapse, shock, etc. They can be severe and potentially fatal and, although less frequent, their incidence has increased in recent years. Risk factors that can determine the severity of an allergic reaction include: the amount of venom inoculated, the type of insect, the patient’s age, the presence of other diseases such as cardiovascular disease or mastocytosis, and the severity of the previous reaction. The probability of suffering a new adverse reaction to another sting is lower when the patient has previously suffered urticaria, compared to other cases, for example, if the previous sting had systemic symptoms, such as bronchospasm or shock.
Insect stings causing the most adverse reactions
The insects that cause the most allergic reactions are hymenoptera, such as bees and wasps. Other types of insects such as mosquitoes, fleas, horseflies, pine processionary, some ticks and spiders can also produce hypersensitivity reactions, usually mild, but more frequently they produce non-allergic reactions. The most problematic hymenopterans are the Vespids and the Apidae.
The most important vespids from an allergenic point of view are the genera Vespa, which are the hornets, and mainly Vespula and Polistes. What we know as Polistes is the “paper wasp”, as they are the wasps present in spring and summer in areas with aquatic spaces, such as ponds and swimming pools, where stings are much more frequent than in the city. The other predominant type of wasp in Spain is the Vespula germánica, known as the terrestrial wasp due to its ability to form hives or nests underground; it usually appears in August and is more resistant to inclement weather, surviving until the beginning of the winter season. The most important aphid genera are Bombus, known as bumblebees, and especially the honey bee, Apis mellifera.
Symptoms to consult an expert and treatment to be applied
All persons presenting a generalized or systemic reaction after a bee or wasp sting should consult a specialist for an allergological study. Also some patients with local reactions, if they are particularly intense or large, may require an allergological study. In all those cases in which a generalized or systemic reaction occurs after a bee or wasp sting, a specialist should be consulted for allergy tests. In the case of some patients with local adverse reactions, if they are particularly intense or large, they may require an allergological study.
The diagnosis is based on the clinical history and the performance of allergic skin and/or analytical tests, in order to investigate the existence of specific Ig E antibodies to the venom. In addition to the symptoms, the history should include all the details of the sting that triggered the reaction, as well as other variables of clinical importance, such as the time of year and the place where it occurred, or whether the sting remained stuck in the skin, in order to try to identify with certainty the type of hymenopteran that stung the patient, This would be essential to establish the composition of the vaccine to be prescribed for the treatment of the allergy, when it is necessary. In addition, it is important to inquire into the patient’s lifestyle history (risk of exposure, quality of life, proximity to medical centers, etc.), which may also condition therapeutic decisions in this regard.
Types of treatment for allergic reactions
Local allergic reactions are treated by applying local cold, antihistamines and topical or systemic corticosteroids, in addition to washing the sting wound with soap and water. In the case of a bee sting, the stinger should be carefully removed without pressing on the venom sac. The basic pharmacological treatment of generalized allergic reactions (anaphylaxis) is adrenaline, especially in moderate and severe reactions, and the effectiveness of this treatment depends on the speed with which it is administered. If a person has suffered a systemic reaction, it is advisable in the future to always carry auto-injectable adrenaline, in the pre-filled syringe format, so that it can be self-administered in the event of a new sting or reaction. In addition, as a second-line treatment, antihistamines and corticosteroids can be administered, the latter (Urbason®, for example) being effective in the prevention of late anaphylactic reactions, but not useful for the management of the acute reaction. In case of a sting, the allergic patient should be taken immediately (once emergency treatment has been administered) to the nearest medical or emergency center. If the symptoms are exclusively cutaneous, the use of antihistamines and corticosteroids may be sufficient. However, in the allergic patient, a very important aspect in the management of these reactions is preventive treatment.
How can an allergic reaction to insects be prevented?
As in other fields of medicine, in this disease it is also better to prevent, and 2 different aspects should be considered from the point of view of preventive treatment. On the one hand, measures aimed at avoiding stings, and on the other hand, treatment aimed at preventing the development of a reaction in the event of a new sting. To reduce the risk of stings, the following basic preventive measures should be observed, especially during the warmer months (when the number of stings increases):
- Exercise caution when hiking, camping or doing any other outdoor activity.
- Always wear shoes outdoors
- Wear clothing that covers most of the body. Do not wear loose-fitting clothing that can be penetrated by insects, or brightly colored, shiny or flowery clothing. Wear clothes of discreet colors.
- Avoid perfumes, lotions, cosmetics, or any product with an intense odor.
- Do not handle fruit or food (especially sugary foods) outdoors.
- Before entering a vehicle, check for insects and keep the windows closed. It is advisable to carry an insecticide spray. If one of these insects enters, you should stop, get out of the car, spray inside with the insecticide spray, close it and make sure that the insect has died or fled before resuming the trip.
- Take special care when traveling by bicycle, motorcycle or convertible car through landscaped areas.
- Do not make quick or sudden movements in the presence of insects. Most insects do not sting unless provoked.
- All nests and hives in the vicinity should be removed by a professional insect exterminator.
- Do not rely on insect repellent products.
In addition, to avoid triggering an allergic or hypersensitivity reaction to a new sting, the allergic patient should be vaccinated with the venom of the hymenopteran to which he/she is sensitized. Specific immunotherapy is indicated in adults suffering from systemic reactions of any type and in children with moderate or severe reactions. Allergic individuals with extensive local reactions (greater than a skin extension of 10 centimeters) are not, in principle, candidates for vaccination, although it can be considered in patients with high associated morbidity and/or low quality of life. The efficacy of the vaccine is clearly demonstrated and it is administered by periodic injections in the forearm for 5 years, after which more than 90% of patients tolerate the insect bite without any reaction. The therapeutic effect is long-lasting and the vaccine also reassures the patient (and his environment), improving his quality of life. The allergist should assess, in discussion with the patient, whether or not vaccination is indicated in a particular case and for how long. The type of reaction suffered after the sting, sensitization, age, risk of exposure, as well as the alteration in the patient’s quality of life, are the most important factors that will determine the need for vaccine treatment.
Problems or risks arising from not treating an allergic reaction
All allergic reactions, as well as those caused by hymenoptera, tend to reproduce themselves, even more severely, after a new contact with the triggering agent or allergen. Patients sensitized to wasp and bee venom have a different risk of developing an allergic reaction after a new sting, depending on the previous reaction suffered. Thus, an extensive local reaction or a generalized cutaneous reaction in children has a lower risk of suffering a systemic reaction in a next sting; on the contrary, both adults and children who have suffered systemic reactions present a high risk of suffering a new generalized allergic reaction. These allergic reactions constitute a serious medical problem since a significant percentage of the population is sensitized to the venom of these insects. These patients (4% of adults and 1% of children) can suffer a systemic allergic reaction and their knowledge and correct diagnosis is very important since treatment with vaccines is very effective, and almost all patients are cured. Therefore, patients who did not receive this treatment would have – if stung again – an increased risk of suffering a new generalized allergic reaction that can be life-threatening.