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of IgE toward allergens to which they have been sensitized and have poorer regulation of responses to those allergens. A sensitization phase in which the individual is “set up” for the reaction (Frazier and Brown 1980) directs lymphocytes to recognize invading allergens as foreign and activates them to produce IgEantibodies. The lymphocytes then release these antibodies, which subsequently bind to receptor sites on mast cells and circulating basophils. The mast cells contain histamine and are located in body tissues such as the respiratory and gastrointestinal tracts, the heart, and the mucous glands and skin. In the sensitized individual, re-exposure to the offending allergen sets in motion a cascade of biochemical events. The allergen crosslinks neighboring IgE antibodies on mast cell and basophil surfaces, which alters the cell membrane and leads to the release of histamine and other chemical mediators. These mediators are capable of contracting smooth muscle in the airways and intestines, as well as dilating blood vessels and increasing vascular permeability. These pathophysiological events may manifest as hives or skin swellings (angiodema), labored breathing, dizziness, or shock. The time interval between a bite or sting and appearance of these symptoms is often short, usually only several minutes. Reactions to stings by Hymenoptera, for example, vary within a continuum ranging from minor to severe. In most cases the reaction is limited to a welt (hive)—a reddened, tender area that causes burning and pain for an hour or two (Greene 2005). In a large local reaction, there is pronounced swelling; sometimes an entire leg or arm will swell from a sting on the toe or finger. The most common systemic reactions are cutaneous: the individual breaks out in hives or urticaria. There is the rare fatal anaphylactic reaction, in which the individual typically dies within 30 to 60 minutes after the sting due to respiratory and cardiovascular complications. These are not toxic reactions, but allergic reactions to proteins in the venom (toxic reactions take hours to days, unless several thousands of stings are received). Causative agents of Anaphylaxis. Since its discovery in the early 1900s, other causative agents of anaphylaxis in addition to venom have been implicated, including foods, which are the most common cause of anaphylaxis outside of the hospital setting (50-100 deaths/ year), medications (especially antibiotics), latex, vaccines, hormones, and sometimes even exercise when associated with a particular food (Kemp 2001; Fireman 1999). Arthropods are by far the most common cause of anaphylaxis due to animal bites or stings, and the insects (particularly Hymenoptera) make up the majority of these cases (see Table 1 for cases of anaphylaxis caused by arthropods that have been determined to be IgE-mediated and Table 2 for other reported cases of anaphylacticlike reactions, so called because these reports lack the definitive in vitro or in vivo tests to demonstrate IgE-mediation). Insects Hymenoptera. It is speculated that the earliest case of an allergic reaction dates back to ancient Egypt (3300 to 2640 BCE), when the Pharaoh Menes supposedly suffered a fatal anaphylactic reaction when stung by a “kheb” during a journey to the “Western Isles”—possibly referring to Britain (Harper 1980). In ancient Egyptian, kheb means hornet or hippopotamus, and to the dismay of the allergists who favor this historical footnote as to the origin of their profession, some Egyptologists have implicated the hippo in the death of King Menes, especially given its abundance in the Nile (Harper 1980). Table 1. Anaphylactic reactions to arthropod bites and stings (evidence for IgE-mediation) (Klotz et al. 2008) Scientific Nomenclature (Common names in parentheses were reported to induce the reaction) Phylum: Arthropoda Class: Insecta Order: Hymenoptera Family: Vespidae Genus: Vespula (ground-nesting yellow jackets) Dolichovespula (aerial-nesting yellow jackets) Vespa (hornets) Polistes (paper wasps) Family: Apidae Genus: Apis (honey bees) Bombus (bumble bees) Family: Formicidae Genus: Solenopsis (fire ants) Pogonomyrmex (harvester ants) Tetramorium Myrmecia (bulldog ants) Pachycondyla (Asian needle and Samsum ants) Formica (wood ants) Order: Hemiptera Family: Reduviidae Genus: Triatoma (kissing bugs) Order: Diptera Family: Tabanidae Genus: Chrysops (deer flies) Tabanus (horse flies) Family: Simuliidae (black flies) Culicidae (mosquitoes) Hippoboscidae (louse flies) Muscidae Genus: Glossina (tsetse flies) Order: Lepidoptera Family: Notodontidae Genus: Thaumetopoea (pine processionary caterpillars) Class: Arachnida Order: Acari Family: Ixodidae Genus: Ixodes holocyclus (Australian paralysis ticks) Ixodes pacificus (western black-legged ticks) Ixodes ricinus Rhiphicephalus Family: Argasidae Genus: Argas (pigeon ticks) Order: Scorpiones Genus: Centruroides (bark and common striped scorpions) Class: Chilopoda (centipedes) About 1% of children and 3% of adults are allergic to stings of Hymenoptera, and at least 40 fatalities occur each year in the United States, with many victims having no previous reactions to stings (Golden 2003). Sting allergies in the U.S. are most commonly due to yellow jackets (Vespula and Dolichovespula) and honey bees (Apis), followed by fire ants (Solenopsis) and paper wasps (Polistes), and less frequently, harvester ants (Pogonomyrmex), hornets (Vespa), bumblebees (Bombus), and sweat bees (Halictidae) (Schmidt 1992). All of these insects, except some sweat bees, are social and most are characterized by central place foraging: worker bees, wasps, and ants leave a nest to find food and then return with it to provide for the colony. The distance traveled to obtain food varies from a few meters for ants to several kilometers for bees. The daily range of the colony’s forays defines its home range or territory. As the colony grows in size, its territory expands to accommodate the increasing American Entomologist • Volume 55, Number 3 135
Table 2. Anaphylactic-like reactions to bites and stings of arthropods (lacking laboratory evidence for IgE-mediation) (Klotz et al. 2008) Scientific Nomenclature (Common names in parentheses were reported to induce the reaction) Phylum: Arthropoda Class: Insecta Order: Hymenoptera Family: Halictidae (sweat bees) Formicidae Genus: Pseudomyrmex (twig ants) Hypoponera Rhytidoponera (green-head ants) Order: Hemiptera Family: Cimicidae Genus: Cimex (bed bugs) Order: Diptera Family: Ceratopogonidae Genus: Culicoides (punkies) Family: Rhagionidae Genus: Symphoromyia (snipe flies) Family: Therevidae Genus: Thereva (stiletto flies) Order: Lepidoptera Family: Anthelidae Genus: Chelepteryx (white-stemmed gum moths) Family: Megalopygidae Genus: Megalopyge (puss caterpillars) numbers of individuals. Their territorial defense is maximal at the nest, which they tenaciously defend against any intruder. In the aculeate Hymenoptera (wasps, bees, and ants), the ovipositor of females has been modified into a stinger, an adaptation that enables these insects to defend their nest against potential predators that would exploit such a concentrated source of food (Schmidt 1986). In many species of ants the stinger is absent or vestigial, but they still possess potent defensive secretions. Although ants are not generally appreciated as causes of anaphylaxis, there are a growing number of species in the U.S. that have been reported to cause this medical emergency (Table 3). Most notorious is the red imported fire ant, Solenopsis invicta, which is widespread in the southeastern U.S. and continuing to expand its range. In some infested urban areas > 50% of the population is stung per year (de Shazo et al. 1990) and as much as 17% of the population is sensitized (Caplan et al. 2003). At least 80 deaths have been attributed to imported fire ants (Rhoades et al. 1989). Particularly vulnerable are the elderly and infirm in nursing homes or hospitals, unable to defend themselves from attack because of limited mobility. Infants represent another vulnerable group to fire ant stings. Two fatalities attributed to southern fire ants, Solenopsis xyloni, were babies less than a year old (Coarsey 1952; Klotz et al. 2004). Nonfatal systemic reactions have been reported for two other native fire ant species, S. aurea and S. geminata (Hoffman 1997), although the native fire ants are generally less aggressive than imported fire ants. Fire ant stings are characterized by an intense burning sensation due to alkaloid compounds (piperidines) in the venom. Each species has its own unique blend of these compounds, but imported fire ant stings are the most severe and typically cause the formation of pseudopustules. Harvester ants possess the most toxic of all insect venoms; in fact, drop for drop, it is more toxic than rattlesnake venom (Schmidt Table 3. Ant species and their geographic distribution in the continental U.S. that have been reported to cause anaphylactic or anaphylactic-like reactions (Klotz et al. 2005b) Scientific Name Range Solenopsis invicta Southern US, New Mexico, California Solenopsis xyloni Southern and southwestern US Solenopsis aurea Southwestern US Solenopsis geminata Southern US Pogonomyrmex rugosus Western Texas and Oklahoma into southern California Pogonomyrmex maricopa West Texas into southern California Pogonomyrmex barbatus Kansas south to Texas into Arizona Pseudomyrmex ejectus Southern US Hypoponera punctatissima Florida, Northeast, Pacific Northwest Pachycondyla chinensis Georgia to Virginia 1978). The sting has been described as “ripping muscles or tendons” and “turning a screw in the flesh” (Schmidt 1986). A neurotoxic component in the venom causes gooseflesh and sweating to occur at the sting site, and often victims develop pain and tenderness in nearby lymph nodes. Allergic reactions to the sting have been reported. For example, of eight patients treated for stings over a one-year period in Tucson, Arizona, four had large local reactions, and four were treated for anaphylaxis (Pinnas et al. 1977). The two species responsible, the Maricopa harvester ant, Pogonomyrmex maricopa, and the rough harvester ant, P. rugosus, are commonly found in urban areas of Tucson (Klotz et al. 2005a). Schmidt et al. (1984) determined that there was significant cross-sensitivity of patients to the various species of harvester ants. Isolated cases of anaphylactic and anaphylactic-like reactions have been reported in the U.S. for ants belonging to several genera. One case reported from South Carolina resulted from the sting of an unidentified species of Tetramorium (Majeski et al. 1974). Two cases in the southeast were due to stings by Pseudomyrmex ejectus (Klotz et al. 2005b), a twig-inhabiting ant that lives in small colonies with typically
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