Summer Bites, Stings, Hives, and Rashes
Insect bites are more than just a bothersome part of summer; on rare occasions, they may lead to more serious conditions, such as Lyme disease (caused by a tick bite) or the West Nile or Zika virus (caused by mosquito bites). Insect bites are puncture wounds or lacerations made by insects such as mosquitos, ticks, gnats, fleas, horseflies, bed bugs, and spiders. An insect may bite when it is agitated and defends itself or when it wants to feed. An insect releases its saliva when it bites the skin, triggering erythema, inflammation, pain, and pruritus at the puncture site. The bites can range in size from a very small papule to a massive welt.
Patients will have varying degrees of reactivity at the site of the bite, depending on skin type and known sensitivities. Bite marks may become infected because of excoriation and rubbing, and they may exhibit signs of infection, such as pus inside or around the bite, swollen glands, fever, and/or flu-like symptoms. Typically, bite marks do not last more than a few hours. However, some patients may have a hyper reaction when the same type of insect bites them for a second time. Once this occurs, the patient becomes sensitized to the insect’s saliva, and a pruritic wheal or papule may develop and last for several days. Because there is no correlation between the size or appearance of the bite mark and the type of biting insect, patient history is critical to diagnosis.
In the majority of cases, reactions to insect bites are mild, local, and straight forward to treat. Patients may find that placing a cold compress over the bite area, applying a topical corticosteroid or anesthetic cream, or taking a non-steroidal anti-inflammatory drug or paracetamol (eg, acetaminophen) may help. In more severe cases, or when the bites are near the eyes, a short course of oral corticosteroids may be needed. Patients should be advised that if an insect bite is uncommonly pruritic, acutely swollen, painful, warm to the touch, or presents with an unusual rash or systemic symptoms (eg, fever, vomiting, nausea, or musculoskeletal complaints), then further evaluation and testing is warranted.
There are 2 major reasons why an insect will bite a particular person: (1) the presence of carbon dioxide production, and (2) the lipid mix on the surface of the skin. For example, mosquitos find humans by determining where carbon dioxide is being produced. Although humans manufacturing carbon dioxide is a given, each individual’s lipid mixture varies and is made up of cholesterol, triglycerides, ceramides, and other fats. Certain lipid mixtures are more appealing to insects than others, which explains why some patients report feeling that they are often a “target” for insect bites.
Since a patient’s skin lipid mix is based on genetics, and knowing that an individual cannot change his or her DNA, the CDC recommends that adults use bug repellents that contain diethyltoluamide (DEET), picaridin, or oil of lemon eucalyptus. Insect repellents containing DEET should not be used on children younger than 2 months, while oil of lemon eucalyptus products should not be used on chil dren younger than 3 years.
When an insect stings an individual and injects its venom into the skin, that patient’s reaction at the site is painful, erythematous, inflamed, and pruritic. However, some patients are allergic to the venom, and these symptoms progress to anaphylaxis in quick order. It is normal for a bee, hornet, yellow jacket, fire ant, or wasp sting to cause a minor rash and localized swelling; however, a more serious systemic reaction leading to anaphylaxis presents with widespread pruritus, urticaria, shortness of breath, swelling of the tongue/throat,nausea, vomiting, or diarrhea.
For mild to moderate reactions, treatment involves removing the stinger as soon as possible, washing the area with soap and water, and applying cold compresses or ice. When removing the insect stinger, a quick scrape with a fingernail is often sufficient. It is important not to pinch the sting or use tweezers, as this can inject more venom into the site. Patients may find relief by applying topical creams (eg, hydrocortisone, aloe, antihistamine) to the affected area.
For anaphylactic reactions, prompt emergency treatment with epinephrine is required. When the patients report experiencing anaphylaxis from an insect sting without prior history of a venom allergy, they should be referred to an allergist for further evaluation. An allergist will perform allergen skin testing as a part of the assessment. Patients who demonstrate sensitivity (positive results) to the skin tests and receive a diagnosis of venom allergy will be considered as candidates for allergy immunotherapy injections. There is no sublingual alternative when desensitizing a patient with a venom allergy.
Patients with a history of venom allergy who have been evaluated by an allergist will know to always carry a 2-pack epinephrine injector set with them and have a plan for emergency action in place. If the epinephrine injector is used, the patient should call 9-1-1, contact his or her health care provider, or go to the nearest emergency department for evaluation of a possible biphasic reaction. A biphasic reaction is a second episode or wave of anaphylaxis, and it occurs without additional exposure to the allergen. It is estimated that biphasic reactions happen in up to 20% of anaphylaxis cases.
Patients should know that if stinging insects are close by, they should remain calm and move slowly away. Because these insects are drawn to brightly colored clothing and perfume, it is best to avoid those when outdoors for a long period of time. The smell of food attracts insects, so awareness is necessary when cooking, eating, or drinking sweet drinks like soda or juice (particularly when drinking from straws or cans, which are common places for stinging insects to hide). At-risk patients should wear closed-toe shoes outdoors, avoid going barefoot, and avoid loose-fitting garments that can trap insects between material and skin.
The Educated Patient
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