AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Background

Insects comprise the most diverse and numerous class of the animal kingdom, Insecta. Human contact with insects is unavoidable. Exposure to biting, stinging, or urticating insects, or to their feces or remains, can range in severity from benign or barely noticeable to life threatening.

Differentiating between insect bites and stings

Many patients confuse insect bites with insect stings and may use the terms interchangeably. Most stinging insects are of the order Hymenoptera, which includes ants, bees, yellow jackets, and wasps. Other stinging organisms are of the class Arachnida, which shares the phylum Arthropoda with insects. These include scorpions, spiders, ticks, and mites.

Bites by classes Insecta and Arachnida

This article is limited to bites by insects and some arachnids. Stings by members of the order Hymenoptera and order Scorpionida are discussed in other articles, as are bites of venomous arachnids in the class Arachnida (spiders) and bites of the order Acarina (mites and ticks).

Injuries from exposure to millipedes (class Diplopoda), centipedes (class Chilopoda), and caterpillars (order Lepidoptera) also are discussed in other articles (see Differentials); however, many of the principles that guide diagnosis and treatment of insect bites also apply to bites and stings of these other organisms.

Exotic insects

While illness related to insect exposure in a particular locale may be easily recognizable, the emergency physician also must be aware of more exotic insect-related diseases as humans travel to more remote areas of the country and the world. Additionally, exotic insects are often kept as pets (sometimes illegally) or can be encountered in shipments of foreign origin.

Anaphylactic shock

Anaphylactic shock is the most notable immediate risk associated with insect exposures. Hypersensitivity to otherwise harmless insect saliva, venom, body parts, excretions, or secretions can cause systemic responses in some individuals. Diagnosing the early phases of a systemic allergic reaction preceding anaphylactic shock is of paramount importance in treating any patient in whom insect exposure is suspected. Severe anaphylaxis can be fatal in as little as 10 minutes.

Diseases transmitted by insect bites

Also crucial is the need to be aware of diseases transmitted by insect bites; Lyme disease, transmitted by ticks, and malaria, transmitted by mosquitoes, are discussed in other articles (see Tick-borne Diseases, Lyme; Malaria).

Chagas disease, increasingly found in the desert southwest and in persons residing in or traveling to Central and South America, should be considered, particularly when the bite site is on the soft skin of the periorbita or lips. Because this infection may produce an acute and chronic illness with notable morbidity and mortality, especially in pediatric patients, clinicians should maintain a high index of suspicion (see Trypanosomiasis).

Mosquito and tick-borne encephalitides such as those produced by the eastern equine virus or the West Nile virus also should be considered in patients presenting with meningismus (see Encephalitis).

Of note, some illnesses transmitted by insects do not produce symptoms until long after the infecting bite. In South America and parts of Africa, blackflies (Simuliidae) are responsible for transmission of onchocerciasis. This illness also is known as river blindness and eventually can produce blindness years after the initial infection. This disease is extremely rare in the United States. Chagas disease, a leading cause of cardiomyopathy in the world, may present latently as well.

Exposure to arthropods may produce dermatitis, cellulitis, urticaria, or blistering unrelated to biting or stinging. Some species of moths, caterpillars, centipedes, beetles, and spiders have urticating hairs or secretions that can cause cutaneous irritation. For further information, please refer to the respective articles on these exposures (see Differentials).

An uncommon occurrence in North America is myiasis by fly larvae. Fly larvae enter the host through varying mechanisms ranging from oviposition of live, burrowing larvae on the host, on or near open wounds, to attachment to other bloodsucking insects. While not generally the result of an insect bite, myiasis can produce pustules and lesions similar to insect bites. These lesions generally contain one or more developing fly larvae. Severe cases of myiasis can cause seizures.

Most, but not all, varieties of larvae capable of myiasis in humans are parasites of other mammals and do not actively seek out human hosts. Human botflies are common in Mexico and Central and South America. New World screwworms are found only in Central and South America; Old World screwworms inhabit Oriental and African tropical regions. (Myiasis by screwworm flies has been reported to be fatal in a few cases.) Wohlfahrtia flies are found in northern regions of North America and the southern Palearctic region. Tumbu flies are found in tropical Africa. Other varieties of fly maggots occasionally may parasitize humans.

Delusional parasitosis is a condition in which patients believe they are infested with tiny imaginary insects. If physical examination of the patient reveals no insects, a thorough examination of the patient's residence and place of work by a qualified entomologist should be conducted before making this diagnosis. These patients often are elderly white women whose delusions may lead them to injure themselves in an effort to rid themselves of the bugs. Similarly, abusers of amphetamines or cocaine may develop a psychosis termed formication (Latin: formica, ant), typified by hallucinations of ants or other bugs crawling over the skin. These patients may harm themselves by deeply gouging their skin in attempts to rid themselves of their imagined infestation. Their wounds may develop an ulcerative scarring impetigo termed ecthyma.

Some patients with hematologic malignancies, such as chronic lymphocytic leukemia (CLL) or mantle cell lymphoma (MCL), have been described as presenting with skin eruptions that mimic insect bites. While a rare entity, suspicion of hematologic malignancy should be considered in patients who have additional systemic symptoms and who lack a clinical history of insect bite or exposure. Even more rarely, an Epstein-Barr virus–associated NK cell lymphoma/leukemia in pediatric patients may present with a hypersensitivity to insect bites.

Insect bites have been implicated in triggering autoimmune syndromes such as leukocytoclastic vasculitis (LCV) or Henoch-Schönlein purpura (HSP). While rare, this possibility should also be considered in rare cases where systemic or progressive symptoms are present.

While plant-eating phytophagous insects can bite in self-defense, their bites generally are not purposeful. This article is limited to discussion of organisms that bite to feed on blood or to catch prey.

Relatively harmless insects

Cockroaches have been reported to bite humans, but their bite generally is harmless. Continued repeated exposure to their remains and feces poses a greater health threat, such as increased incidence of asthma, especially in inner cities, and their remains and feces are possible vectors for transmission of viral and bacterial diseases.

Earwigs generally are harmless insects that have earned an unpleasant reputation. This may be because of their depiction in popular culture, such as in the television series, "The Night Gallery." Although they appear to have a large pincer on the posterior abdomen, it is not capable of rendering anything more serious than a mild pinch. Additionally, and contrary to popular belief, they do not routinely enter human ear canals and parasitize humans. Cockroaches are much more likely to be found lodged in a patient's auditory passage.

Pathophysiology

Mouthparts of biting insects can be classified into 3 broad groups: piercing and/or sucking, sponging, and biting and/or chewing. Tremendous diversity exists in the morphology of these groups. Insects discussed in this article generally are nonvenomous, yet many species inject saliva while biting. Their saliva may aid in digestion, inhibit coagulation, increase blood flow to the bite, or anesthetize the bite locus. Most lesions are the result of the victim's immune response to these insect secretions. In the case of Chagas disease, the infective organism is transmitted via the feces of a reduviid bug, which enters through the bite site when the wound becomes pruritic and is scratched.

Other than horsefly bites, most insect bites are minor puncture wounds to the skin. Horseflies feed with a large scissorlike proboscis that can cause a relatively deep and painful wound.

Anaphylactic reactions may occur among atopic individuals bitten by an insect or other arthropod to which they have developed an allergy. Allergy also may develop in response to exposure to arthropod body parts or waste products. Refer to Anaphylaxis for treatment of this response.

Frequency

United States

Reliable statistics are not available.

International

Reliable statistics are not available for insect bite exposures because most cases are not reported and do not require hospital care. A study in tropical Zimbabwe, where biting insects are common, found that 1.5% of hospital admissions were related to insect exposure, including both bites and stings. A vast majority of these were arachnid or Hymenoptera related.

Mortality/Morbidity

Mortality associated with insect bites is from hypersensitivity reactions, either anaphylactic (IgE-mediated) or anaphylactoid (non-IgE-mediated), or from complications resulting from infection. Reliable figures on incidence and prevalence are not available. Estimates of mortality from insect-provoked anaphylaxis in the United States range from 50-150 persons annually. In Arizona, for example, death from reduviid-associated anaphylaxis has been reported as a leading cause of death from insect exposure. Worldwide, the greatest morbidity and mortality associated with insect bites are due to Anopheles species mosquito bites resulting in infection with malaria (see Malaria).

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

History

Most patients are aware of bites when they occur or shortly thereafter. Frequently they observe the insect as well. Reactions to insect bites can be classified as local, severe local, or systemic.

• Reactions to bites may be delayed due to the host being asleep or because the saliva of some micropredators may contain an anesthetic secreted to allow uninterrupted blood-feeding.
• In a local reaction, the patient may complain of discomfort, moderate or severe pain, erythema, tenderness, warmth, and edema of tissues surrounding the bite site.
• In a severe local reaction, complaints include generalized erythema, urticaria, and pruritic edema.
• In a systemic response, the patient may complain of localized symptoms as well as symptoms not contiguous with the bite location. Early complaints typically include generalized rash, urticaria, pruritus, and angioedema. These symptoms may progress, and the patient may develop anxiety, disorientation, weakness, gastrointestinal disturbances (eg, cramping, diarrhea, vomiting), uterine cramping in women, urinary or fecal incontinence, dizziness, syncope, hypotension, stridor, dyspnea, or cough.
• Patients who present with a history of homelessness or of staying in homeless shelters may have an exposure to organisms such as bedbugs. Alternatively, patients with impairment from mental illness may also be susceptible to infestation with insect parasites.
• Exposure to feral animals or even to domesticated animals, such as livestock or house pets, may predispose patients to exposure to biting insects such as fleas, bedbugs, or lice.

Physical

• Without a clear patient history, diagnosis of an insect bite can be difficult since the initial response may be limited to erythema, local pain, pruritus, or edema.
• Wheals and urticaria are common initial signs and generally appear within a few minutes of the bite. Unfortunately, many dermatologic conditions also produce similar cutaneous signs and may confound the diagnosis.
• Identification of the insect responsible for the bite may be possible by examining the location, number, pattern, and sequelae of the bite(s).
• Physical examination elements indicating a systemic reaction include the following:
• • Cardiovascular - Hypotension, orthostasis
  • Cutaneous - Urticaria, wheals, angioedema, blood at bite site, pruritus
  • Respiratory - Tachypnea, stridor, wheezing, bronchospasm
  • Gastrointestinal - Hyperactive bowel sounds

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Lab Studies

• Lab studies seldom are necessary. If the patient is compromised severely and requires hospital admission or end organ failure is suspected, order appropriate laboratory studies.
• Biopsies of lesions generally are nondeterminant and are impractical in the ED.
• Microscopic examination of skin scrapings can be useful in the diagnosis of scabies or mite infestations but are not useful for most insect bites.
• Serology studies may be useful in determining infection due to an insect vector, but these are not available in the ED and may take weeks to obtain a result.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Prehospital Care

• Most insect bites may be treated acutely with a compress after routine wound cleaning. A cleansing solution of 1 part household bleach to 9 parts water may minimize pain and help cleanse the wound to prevent secondary infection.
• For a large local reaction, ice packs may minimize swelling. Apply ice for no more than 15 minutes at a time using a cloth barrier between ice and skin to prevent direct thermal injury to the skin.
• Epinephrine is the mainstay of prehospital treatment of a systemic reaction; the route of administration (subcutaneous, intramuscular, intravenous [IV], endotracheal) depends on the patient's condition and the expertise of the prehospital provider. Systemic antihistamines and corticosteroids, if available, help manage systemic reactions. Many patients who are allergic to stings carry commercially available bee sting kits containing an autoinjector of epinephrine. Refer to Bee and Hymenoptera Stings.
• Topical antihistamines should not be applied over large surface areas, nor should they be used concurrently with systemic H1 antihistamines. Systemic anticholinergic toxicity may result from misuse of these medications. Use of H2-blocking drugs (usually used to reduce gastric acid secretion) may be used concurrently with H1-blocking antihistamines.
• In many patients, transport to a hospital is not necessary. Those requiring transport include patients who develop signs or symptoms of a systemic response or individuals with a history of insect-related anaphylaxis. A phone call to the regional poison center may save a costly visit to the ED.

Emergency Department Care

• Endotracheal intubation and ventilatory support may be required for severe anaphylaxis or angioedema involving the airway.
• Treat emergent anaphylaxis in an atopic individual with an initial subcutaneous injection of 0.3-0.5 mL of 1:1000 epinephrine. This may be repeated every 10 minutes as needed.
• A bolus of IV epinephrine (1:10,000) may be used cautiously in severe cases.
  • Solution of 1:10,000 typically is found in 10-mL vials. Repeated 1-mL doses are a reasonable initial approach in a critically ill patient with anaphylaxis.
  • Once a positive response is achieved, these boluses can be followed by a carefully monitored, continuous epinephrine infusion.
  • Use extra care in monitoring formulation, concentration, and dose when administering IV epinephrine to avoid inadvertent overdoses.
• Severely hypotensive patients may require large volumes of IV fluids. Monitor patients for angioedema and pulmonary edema.
• Antihistamines, both H1 and H2 blockers, are useful in treating systemic reactions. Corticosteroids also are indicated routinely in such patients.
• Refer to Anaphylaxis and Serum Sickness for further guidance.
• Ensure appropriate tetanus prophylaxis.

Consultations

• In cases in which determining the insect species is important, a health department, agriculture extension, or university entomologist may be useful.
• In cases of potential vector-borne disease transmission, an infectious disease specialist may be of help.
• If the potential infection is associated with travel to a tropical region, consider contacting a tropical medicine specialist or the Centers for Disease Control and Prevention (CDC) at 1-877-394-8747 (Traveler's Health Hotline).
• A regional poison center may be of assistance in difficult or complicated cases or for general information.

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Goals of therapy are to treat anaphylaxis and prevent complications.

Drug Category: Cardiovascular agents

Act to decrease the muscle tone in the small and large pulmonary airways and increase vascular tone.

Drug Category: Bronchodilators

Through activation of cyclic AMP, beta agonists stimulate the ATPase pump, thereby shifting potassium into the intracellular compartment and stimulating an adrenergic response.

Drug Category: Antihistamines

Prevent histamine response in sensory nerve endings and blood vessels; more effective in preventing histamine response than in reversing it. H2 antihistamines are useful in treatment of anaphylactic reactions when used concomitantly with H1 antagonists. Many H2 blockers are available. Cimetidine is the prototype drug.

Drug Category: Corticosteroids

Have anti-inflammatory properties and cause profound and varied metabolic effects. In addition, these agents modify the body's immune response to diverse stimuli. Methylprednisolone is a typical drug of this class.

Drug Category: Toxoids

For active immunity against tetanus.

Drug Category: Immunoglobulins

Consists of administration of immunoglobulins pooled from serum of immunized patients.

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Further Inpatient Care

• Patients with true anaphylaxis, particularly if associated with hypotension, often are admitted for monitoring or observation in the ED upon recovery. Accepted definition of "true" anaphylaxis requires the involvement of at least 2 of the following 4 systems: cardiovascular, gastrointestinal, skin, or respiratory. Literature provides no clear direction on who needs admission. Certain patients with a disease transmission (eg, malaria) may require admission.

Further Outpatient Care

• Follow-up monitoring for infection is advised for individuals bitten by an insect known to transmit a secondary disease, if exposed to the vector in an endemic area (eg, Chagas disease in the case of kissing bugs [Reduviidae]).
• Individuals who recover from a systemic reaction should consult with an allergist regarding desensitization measures.

In/Out Patient Meds

• Prescribe a bee sting kit with a device for self-administration of epinephrine prior to discharge if the patient had a systemic response to an envenomation (see Bee and Hymenoptera Stings).
• Corticosteroids and antihistamines usually are continued for a few (3-4) days after a systemic response. Serum sickness reactions may require longer therapy (see Serum Sickness).

Deterrence/Prevention

• Patients may be educated about avoidance measures. Refer to the section on Patient Education in this article.

Complications

• Secondary infection may result.
• Symptoms of disease transmitted by insect bites may not be evident for days, weeks, or even longer.

Prognosis

• Prognosis generally is good except in patients with severe untreated anaphylaxis or in those with chronic or invasive infections.

Patient Education

• Biting insects are ubiquitous in nearly all parts of the world, yet certain measures can be taken to minimize risk of exposure.
• • Periodic pest control may eliminate nests and minimize reproduction of biting insects.
  • Wear protective clothing (ie, long pants, long sleeves), especially when outdoors. Many insects are incapable of biting through clothing. Additionally, light-colored clothing appears to be less attractive to many biting insects, including mosquitos. Avoid dark colors or brightly colored floral patterns. Wear protective footwear. Wear gloves when working with soil or in areas of heavy infestation.
  • Avoid use of heavy perfumes, scented soaps, sprays, or lotions that may attract insects.
  • Be aware of surroundings; for example, avoid dense vegetation or animals suspected of carrying fleas, chiggers, or ticks.
  • Prudent and cautious use of insect repellent can help minimize exposure to insect bites and stings.
  • Be aware of the potential for bees or other foraging insects to enter opened soft drink containers that are left idle.
• For excellent patient education resources, visit eMedicine's Bites and Stings Center. Also, see eMedicine's patient education articles Insect Bites, Allergy: Insect Sting, Severe Allergic Reaction (Anaphylactic Shock), Black Widow Spider Bite, Brown Recluse Spider Bite, and Ticks.

MISCELLANEOUS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• Failure to recognize early warning signs of anaphylaxis
• Failure to obtain a thorough travel or exposure history
• Failure to consider or recognize exotic diseases or diseases with vague prodromal signs and symptoms
• Failure to refer questionable cases for reasonable follow-up care
• Failure to warn patients about possible complications secondary to bites such as infection, serum sickness, and, in atopic individuals, biphasic anaphylaxis
• Failure to provide a referral to an allergist or to prescribe a bee sting kit to patients with systemic reactions

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

• Asada H, Miyagawa S, Sumikawa Y, et al. CD4+ T-lymphocyte-induced Epstein-Barr virus reactivation in a patient with severe hypersensitivity to mosquito bites and Epstein-Barr virus-infected NK cell lymphocytosis. Arch Dermatol. Dec 2003;139(12):1601-7. [Medline].
• Auerbach PS, ed. Wilderness Medicine. 4th ed. 2001.
• Blum J, Beck BR, Brun R, Hatz CH. Clinical and serologic responses to human 'apathogenic' trypanosomes. Trans R Soc Trop Med Hyg. Oct 2005;99(10):795-7. [Medline].
• Busvine JR. Disease Transmission by Insects: Its Discovery and 90 Years of Effort to Prevent it. Springer Verlag; 1993:11-74.
• Davis CL. Insects, allergy and disease. In: Allergic and Toxic Responses to Arthropods. 1979;300-9.
• Edwards L, Lynch PJ. Anaphylactic reaction to kissing bug bites. Ariz Med. Mar 1984;41(3):159-61. [Medline].
• Garcia LS, Bruckner DA. Diagnostic Medical Parasitology. 3rd ed. Amer Society for Microbiology; 1997.
• Goddard J. Physician's Guide to Arthropods of Medical Importance. CRC Press;1996.
• Hoffman DR. Allergic reactions to biting insects. In: Levine MI, Lockey RF, eds. Monograph on Insect Allergy. 1981:69-74.
• Khamaysi Z, Dodiuk-Gad RP, Weltfriend S, et al. Insect bite-like reaction associated with mantle cell lymphoma: clinicopathological, immunopathological, and molecular studies. Am J Dermatopathol. Aug 2005;27(4):290-5. [Medline].
• Krause RS. Immune system disorders, hypersensitivity. In: Aghababian R, ed. Emergency Medicine: The Core Curriculum. Lippincott Williams & Wilkins Publishers; 1998:417-22. [Medline].
• Lane RP, Crosskey RW. Medical Insects and Arachnids. Chapman & Hall; 1993.
• Lynch PJ, Pinnas JL. "Kissing bug" bites. Triatoma species as an important cause of insect bites in the southwest. Cutis. Nov 1978;22(5):585-91. [Medline].
• Mieller UR. Insect Sting Allergy: Clinical Picture, Diagnosis, and Treatment. Gustav Fischer; 1990:144-7.
• Moffitt JE, Yates AB, Stafford CT. Allergy to insect stings. A need for improved preventive management. Postgrad Med. Jun 1993;93(8):197-9, 203-4, 207-8. [Medline].
• Nhachi CF, Kasilo OM. Poisoning due to insect and scorpion stings/bites. Hum Exp Toxicol. Mar 1993;12(2):123-5. [Medline].
• Shai A, Halevy S. Direct triggers for ulceration in patients with venous insufficiency. Int J Dermatol. Dec 2005;44(12):1006-9. [Medline].
• Soylu A, Kavukcu S, Erdur B, et al. Multisystemic leukocytoclastic vasculitis affecting the central nervous system. Pediatr Neurol. Oct 2005;33(4):289-91. [Medline].
• Ter Poorten MC, Prose NS. The return of the common bedbug. Pediatr Dermatol. 2005;22(3):183-7.
• Tokura Y, Ishihara S, Tagawa S, et al. Hypersensitivity to mosquito bites as the primary clinical manifestation of a juvenile type of Epstein-Barr virus-associated natural killer cell leukemia/lymphoma. J Am Acad Dermatol. Oct 2001;45(4):569-78. [Medline].

Article Last Updated: Mar 21, 2006