Insect Bites 

Insects are arthropods of the class Insecta. Insects have an adult stage characterized by a hard exoskeleton, 3 pairs of jointed legs, and a body segmented into head, thorax, and abdomen. Insects comprise the most diverse and numerous class of the animal kingdom and include numerous species of praying mantis, dragonflies, grasshoppers, true bugs, flies, fleas, bees, wasps, ants, lice, butterflies, moths, and beetles. The number of species is estimated at between 6 and 10 million, with more than a million species already described. Insects represent more than half of all known living organisms and potentially represent more than 90% of the differing life forms on Earth. Hence, human contact with insects is unavoidable. Exposure to biting or stinging insects or to their remains can range in severity from benign or barely noticeable to life threatening.

See the images below.

Differentiating between insect bites and stings

Many patients confuse an insect bite with a sting and may use the terms interchangeably. A bite is usually from mouth parts and occurs when an insect is agitated to defend itself or when an insect seeks to feed. Bites from mosquitoes, fleas, bed bugs, and mites are more likely to cause itching than pain.

See the images below.

A stinging apparatus is usually a sharp organ of offense or defense, especially when connected with a venom gland, and adapted to inflict a wound by piercing, as the caudal sting of a scorpion. The stinger is typically located at the rear of the animal. Animals with a stinger include bees, wasps, hornets, and scorpions. Most stinging insects are of the order Hymenoptera, which includes ants, bees, and wasps. Hymenoptera stings result in more fatalities than stings or bites from any other arthropod. Wasps can bite and sting at the same time (See Wasp Stings).

Since their introduction into the southern United States in the 1920s, imported fire ants anchor themselves with their mandibles and subsequently inflict a sting. Fire ants often pivot or re-anchor themselves only to sting again and again resulting in a sensation of fire at the site. When fire ants swarm, they often position themselves on their victim and sting simultaneously in response to an alarm pheromone released by one or several individuals. Immobilized or elderly patients can become rapidly covered by swarms of these ants, resulting in severe stings and even death (See Fire Ant Bites).

Bites by classes Insecta

This article is limited to bites by insects and not 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 must also 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.

The reoccurrence rate is 40-60% for insect stings. Hence, the patient should be instructed on how to avoid future exposure to the causative agent, if possible. A prescription and clear instructions on the use of an epinephrine autoinjector should be provided to patients when the risk of another reaction is judged to be substantial.^[1]

Diseases transmitted by insect bites

The need to be aware of diseases transmitted by insect bites is crucial; 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 America or South America, should be considered, particularly when the bite site is on the soft skin of the periorbita or lips.^[2] 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 is also 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. Obtaining a history of international travel is important because this information can lead to a diagnosis that would otherwise be overlooked. Determining the destination, time of year, length of stay, and time since travel are all important pieces of history to obtain.

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.

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 the human ear canal and parasitize humans. Cockroaches are much more likely to be found lodged in a patient's auditory passage.

Mouthparts of biting insects can be classified into 3 broad groups: piercing, sponging, and biting. 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. Most insect bites are minor and can result in superficial puncture wounds to the skin. Horseflies feed with a large scissorlike proboscis that can cause a relatively deep and painful wound.

Frequency

United States

In the United States, the American Association of Poison Control Centers reported 42,620 cases of exposures to insects in 2007. Just more than 200 of these were listed as resulting in moderate or major reactions. A moderate reaction is defined as signs or symptoms that were more pronounced or systemic, whereas a major reaction is life-threatening or lead to significant residual disability. Fatalities among these exposures are rarely reported to poison centers and usually result from allergic reactions to Hymenoptera stings. Because of underreporting, these numbers are only a glimpse as to what is actually occurring.^[3]

International

Reliable statistics are not available for insect bite exposures because most cases are not reported and do not require hospital care.^[4] 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 (immunoglobulin E [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).^[4]

Sex

No sexual preference known.

Age

No age preference known.