Insect Bites

Stings and bites from insects are common. They often result in redness and swelling in the injured area. Sometimes a sting can cause a life-threatening allergic reaction.

Arthropods are insects that live primarily on land and have 6 legs. They dominate the present-day land fauna. They represent about three-fourths of known animal life. In fact, the actual number of living species could range from 5-10 million.

The orders that contain the greatest numbers of species are Coleoptera (beetles), Lepidoptera (butterflies and moths), Hymenoptera (ants, bees, wasps), and Diptera (true flies).

Insects do not usually attack unless they are provoked. Most bites and stings are defensive. The insects sting to protect their hives or nests.

A sting or bite injects venom composed of proteins and other substances that may trigger an allergic reaction in the victim. The sting also causes redness and swelling at the site of the sting.

• Bees, wasps, hornets, yellow jackets, and fire ants are members of the Hymenoptera family. Bites or stings from these species may cause serious reactions in people who are allergic to them. Death from bee stings is 3-4 times more common than death from snake bites (for more information, see stings of bees and wasps). Bees, wasps, and fire ants differ in how they inflict injury.
  
  
  • When a bee stings, it loses the entire injection apparatus (stinger) and actually dies in the process. A wasp can inflict multiple stings because it does not lose its injection apparatus after it stings.
    
    
  • Fire ants inject their venom by using their mandibles (the biting parts of their jaw) and rotating their bodies. They may inject venom many times.
  
  
• In contrast, bites from mosquitoes typically do not cause significant illnesses, unless they convey "vectors," or microorganisms that actually live within these mosquitoes. For instance, malaria is caused by an organism that spends part of its life cycle in a particular species of mosquitoes. West Nile virus is another disease spread by a mosquito.
  
  
• Other types of insects, bites, and diseases
  
  
  • Lice can transmit epidemic relapsing fever, caused by spirochetes.
    
    
  • Leishmaniasis, caused by the protozoan Leishmania, is carried by a sand fly.
    
    
  • Sleeping sickness in humans and a group of cattle diseases that are widespread in Africa, and known as nagana, are caused by protozoan trypanosomes transmitted by the bites of tsetse flies.
    
    
  • In unsanitary conditions, the common housefly can play an incidental role in the spread of human intestinal infections (such as typhoid and bacillary and amebic dysentery) by contamination of human food.
    
    
  • Tularemia can be spread by deer fly bites, the bubonic plague by fleas, and the epidemic typhus rickettsia by lice.
    
    
  • Various mosquitoes spread viral diseases (such as equine encephalitis; dengue and yellow fever in humans and other animals).
    
    
  • Ticks can transmit Lyme disease and other illnesses through their bites or stings.
    
    
  • Other insects such as chiggers and mites typically cause self-limited localized itchiness and swelling.
    
    
  • Serious bites from spiders, which are not insects, can be from the black widow or brown recluse.

The response to a sting or bite from insects is variable and depends on a variety of factors. Most bites and stings result in pain, swelling, redness, and itching to the affected area. The skin may be broken and become infected if the bite area is scratched. If not treated properly, these local infections may become severe and cause a condition known as cellulitis.

You may experience a severe reaction beyond the immediate area of the sting if you are allergic to the bite or sting. This is known as anaphylaxis. Symptoms of a severe reaction include hives, wheezing, shortness of breath, unconsciousness, and even death within 30 minutes.

A sting on the tongue may cause throat swelling and death because of airway obstruction.

Stings from large hornets or multiple (hundreds or thousands) bee stings have been rarely reported to cause muscle breakdown and kidney failure.

Bites from a fire ant typically produce a pustule, or a pimple-like sore, that is extremely itchy and painful.

If you start to experience symptoms that are not just at the site of the bite or sting (and you don't have a history of severe reactions), seek medical attention. These symptoms (systemic symptoms affect the whole body) may progress to fatal anaphylactic shock.

Hives are the most common systemic symptom. They appear as irregular, raised, red blotchy areas on the skin and are very itchy. If hives are the only systemic symptom present, they are often treated at home with an antihistamine.

If the bite appears infected (redness with or without pus, warmth, fever, or a red streak that spreads toward the body), see a doctor.

If you don't know what bit you, it is important to keep watching the area closely to be sure it does not become infected. Call your doctor if there is an open wound, which may suggest a poisonous spider bite.

People who have a history of severe reactions should go to the nearest hospital's emergency department after a bite or sting if they experience any symptoms. Those who have no history of severe reactions should also go to the emergency department if they have any of the following symptoms:

• Wheezing
  
  
• Shortness of breath
  
  
• Chest tightness or pain
  
  
• Sensation of the throat closing or difficulty speaking or swallowing
  
  
• Faintness or weakness
  
  
• Infection (If the wound appears infected and you are not able to reach your doctor, seek care at a hospital.)

The diagnosis of a reaction to a bite or sting is usually obvious from the history. The doctor will perform a physical examination to look for effects of the bite or sting on various parts of the body. Examination of the skin, respiratory system, cardiovascular system, and oral cavity are particularly important.

|Self-Care at Home|

Treatment depends on the type of reaction. If there is only redness and pain at the site of the bite, application of ice is adequate treatment. Clean the area with soap and water to remove contaminated particles left behind by some insects (such as mosquitoes). These particles may further contaminate the wound if not removed. Refrain from scratching because this may cause the skin to break down and an infection to form.

You may treat itching at the site of the bite with an over-the-counter antihistamine such as diphenhydramine (Benadryl) in cream or pill form. Calamine lotion also helps relieve the itching.

People who have a history of severe reactions to bites or stings may have been prescribed an anaphylaxis kit. The kit contains an epinephrine injector (you give yourself an injection), tourniquet, and an antihistamine. The kit should be used according to the doctor's instructions.

|Medications|

Severe reactions are treated with injections of epinephrine and an antihistamine such as diphenhydramine (Benadryl). Steroids (drugs in the cortisone family) are also usually given. Oral antibiotics may be given for infected bite wounds. For seriously ill people, an IV will be started, oxygen given, and a heart monitor used until the symptoms have improved.

After emergency treatment, antihistamines are taken for a short period of 3-5 days. Steroids (cortisone-type drugs) may also be prescribed.

|Follow-up|

In the emergency department, you may be instructed how to use an emergency kit in case of future stings to prevent a severe reaction. The anaphylaxis kit contains an epinephrine injector, tourniquet, and an antihistamine.

You may be referred to an allergist for desensitization therapy. After testing to determine which venom you are sensitive to, the doctor will gradually increase the doses of venom injected over time. Desensitization is usually effective in preventing a severe reaction to future stings.

|Prevention|

You can minimize your exposure to insect bites by changing your patterns of activity or behavior.

• Some vector mosquitoes are most active in twilight periods at dawn and dusk or in the evening, so avoid outdoor activity during these periods.
  
  
• Wear long-sleeved shirts, long pants, and hats to minimize the areas of exposed skin. Shirts should be tucked in.
  
  
• Use insect repellants. Repellents applied to clothing, shoes, tents, mosquito nets, and other gear will enhance protection.
  
  
  • Permethrin-containing repellents (Permanone) are recommended for use on clothing, shoes, bed nets, and camping gear. Permethrin is highly effective as an insecticide/acaricide (against ticks and mites) and as a repellent. Permethrin-treated clothing repels and kills ticks, mosquitoes, and other arthropods and retains this effect after repeated laundering. Such treated clothing is thought to pose little danger for poisoning to humans wearing it.
    
    
  • Repellents containing DEET (N,N-diethylmetatoluamide) as an active ingredient are recommended by most authorities. A common commercial repellant that contains this chemical is the brand name OFF. DEET repels mosquitoes, ticks, and other arthropods when applied to skin or clothing. Formulations containing less than 35% DEET are recommended because the additional gain in repellent effect with higher concentrations is not significant when weighed against the potential for toxicity, which include rare cases of encephalopathy (brain infection) in children.

|Outlook|

Most people respond well to home or emergency treatment. People with very severe reactions or those who do not respond to initial treatment will often require hospital admission for further treatment and monitoring. A severe episode may be fatal in spite of appropriate medical treatment.

anaphylaxis, severe allergic reaction, anaphylactic shock, bee sting, wasp sting, fire ant sting, hornet sting, yellow jacket sting, allergy, bee sting kit, mosquito bite, malaria, West Nile virus

Author: An T Nguyen, MD, Staff Physician, Department of Emergency Medicine, Buffalo General Hospital.

Editors: Marian Gambrell, MD, Clinical Assistant Professor, Department of Emergency Medicine, St Lukes-Roosevelt Hospital Center, Columbia University; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, ; Anthony Anker, MD, FAAEM, Attending Physician, Emergency Department, Mary Washington Hospital, Fredericksburg, VA.