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Allergy to non-Hymenoptera insect bites and stings

Although most insect bites and stings cause only mild discomfort such as pain and swelling, some can cause more serious allergic reactions.
 

Dr Albéndiz, allergy specialist at HC Marbella, explains how to recognise and treat these reactions, especially from insects such as mosquitoes, pine processionary caterpillars, spiders, scorpions and ticks.
 

Mosquitoes

There are more than 3,500 known mosquito species, of which only a few are known to produce allergic reactions. The bite is usually harmless, although it can sometimes be a vehicle for transmission of pathogens and trigger immune reactions in the host. This response is triggered by the mosquito saliva, where the main allergens are found.
 
Typical reactions to mosquito bites can be immediate (with the appearance of a 2-10 mm wheal, redness and/or itching within a few minutes) or delayed (with the appearance of papular lesions, associated with itching and oedema after several hours).
 
The Skeeter syndrome characterises patients who, after a mosquito bite, present extensive local reactions accompanied by fever. It usually occurs in healthy children and may mimic cellulitis (red, hot, swollen and sore skin), but usually differs from the latter in that it appears within a few hours after a mosquito bite. It usually resolves within 3-10 days.
 
Severe mosquito bite reactions are very rare. People at greatest risk are those with high exposure (outdoor workers), those lacking acquired immunity to local mosquitoes (children and immigrants) and the immunocompromised.
 
In general, over the years, a desensitisation usually occurs as a result of natural exposure. This process can last from 2 to 20 years.
 
The cornerstone of mosquito allergy treatment is based on avoidance measures. Local mosquito populations can be reduced by eliminating areas of stagnant water, rearing fish in ponds to consume mosquito larvae and the use of appropriate insecticides.
 
When exposure to mosquitoes is expected, it is advisable to protect oneself with appropriate clothing and chemical repellents such as N,N-Diethyl-meta-Toluamide (DEET). DEET is the most effective repellent, it can be applied to skin or clothing and can be used on children over 2 months of age in concentrations of 10-30% (higher concentrations may cause local toxic effects or dermatitis).

Pine Processionary caterpillar

This caterpillar inhabits pine trees, although there is a variant that can be found on oak trees.
 
Usually, the reactions produced by the Pine Processionary occur in the areas of contact by penetration of its setae or „hairs“, producing contact urticaria. In children, the typical reaction is on the palms of the hands and interdigital spaces, as they often try to catch the caterpillars.
 
In addition to skin involvement, conjunctivitis and respiratory distress have been reported in the context of anaphylaxis, although these cases are exceptional.
 
For diagnostic purposes, it is important to be on the alert when people with this type of skin lesion have been exposed to a pine forest area over the previous 24 hours.

Spiders

Spider bites to humans are usually accidental and may go unnoticed at first. The most frequent reactions are due to 2 genera of spiders:

• 1. Latrodectus: It has a worldwide distribution. Symptoms appear more than an hour after the bite and vary from local pain (the most frequent) to muscle contractions, tremor, tachycardia or neurological disturbances. Treatment is usually symptomatic.

 

• 2. Loxosceles: They inhabit tropical areas and their bite is more frequent in spring and summer. They usually produce cutaneous symptoms, consisting of the appearance of a purplish plaque with irregular contours, associated with intense redness and oedema, producing a lot of pain. Over a period of hours, a crust appears, which falls off after several weeks. In severe and exceptional cases, it can cause blood, renal, hepatic or cardiac alterations between 12-24 hours after the bite. Treatment is symptomatic.

Scorpions

The incidence of reactions to scorpion stings in Spain is low, and no fatal cases have been reported. Most of them are usually mild and can be classified into 3 possible clinical stages:
 
Treatment is symptomatic, consisting of analgesia and the application of local cold to the area of the sting.

• Stage I: Intense local pain and swelling at the site of inoculation.

 

• Stage II: Additionally, this stage presents fever, vomiting, diarrhoea, respiratory distress or hypotension.

 

• Stage III: The most severe clinical form, producing pulmonary and cardiac alterations or cyanosis. It must be treated in the Intensive Care Unit (ICU).

Treatment is symptomatic, with analgesia and the application of local cold to the site of the sting.

Ticks

Reactions associated with tick bites include allergic reactions from the bite itself and alpha-gal syndrome.
 
The most common reaction to tick bites is local swelling with associated itching. Severe cases (anaphylaxis) due to allergy to some components of their saliva have also been documented. These severe reactions usually occur when an attempt is made to abruptly remove the tick from the skin, as the tick then attaches more strongly and injects more saliva. This is why, if a tick is attached, it is best to kill it first before removing it, so as to avoid handling it alive.
 
Alpha-gal syndrome is caused by an allergy to an oligosaccharide called Galactose-Alpha-1,3-Galactose, which is present in many non-primate mammalian proteins but not in humans. Ticks often contain blood from the non-primate mammals they parasitise and, by biting humans, they may thus transfer some of this blood to humans. As a result, the immune system of the bitten individual could develop IgE antibodies to this oligosaccharide and become sensitised. This could be related to 2 types of severe allergic reactions:
 

• 1. Food allergy to certain mammalian meats (beef, lamb, pork), which usually produces severe allergic symptoms within 3-6 hours after ingestion of these types of meat.

 

• 2. Allergy to Cetuximab, which is a drug used in oncology for the treatment of colon cancer and some head and neck tumours. This drug has some components of human origin and others derived from rodents, the latter containing Galactose-Alpha-1,3-Galactose.

 

 
 

Dr. Vicente Albendiz
Specialist in allergology

August 7, 2024