Introduction
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
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:
More on Bites, Insects |
 Overview: Bites, Insects |
| Differential Diagnoses & Workup: Bites, Insects |
| Treatment & Medication: Bites, Insects |
| Follow-up: Bites, Insects |
| References |
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Further Reading
Keywords
Insecta, Hymenoptera, Arachnida, anaphylactic shock, lyme disease, Chagas disease, trypanosomiasis, tick-borne encephalitides, blackflies, Simuliidae, onchocerciasis, river blindness, dermatitis, cellulitis, urticaria, myiasis, fly larvae, human botflies, New World screwworms, Old World screwworms, Wohlfahrtia flies, Tumbu flies, fly maggots, delusional parasitosis, formication, scarring impetigo, ecthyma, plant-eating phytophagous insects, cockroach bite, earwigs, reduviid bug, horsefly bites, Anopheles mosquito, malaria, urticaria, angioedema, syncope, stridor
