Hymenoptera Stings
Section snippets
Lethal Dose
Death can result from insect stings in a few different manners. Most deaths related to Hymenoptera stings are the result of immediate hypersensitivity reactions causing anaphylaxis. However, death may also occur from severe local reactions, particularly if involving the airways with subsequent respiratory obstruction. Massive envenomation, as seen in swarm attacks, can likewise cause death in nonallergic individuals. In humans, the estimated lethal dose is about 500 stings for adults.6 The
Toxicokinetics
The venom of stinging insects contains several powerful allergens and pharmacologically active compounds. Hymenoptera venoms are composed of complex mixtures of allergic proteins, active antigens, and peptides.10 Both bee and wasp venoms are made up primarily of protein. Bee venom is a complex mixture of biologically active components, primarily consisting of proteins, enzymes, and amines.
Clinical Signs and Manifestations
Typically, honeybee stings are manifested as localized edema without a systemic reaction. Unlike venomous spider bites, venom of all Hymenoptera causes some degree of local swelling and pain, and victims know that they have been stung. Generally the small local reaction of erythema, edema, and pain at the site of the sting is a self-limiting, non-IgE-mediated condition, which spontaneously resolves within 24 hours. Occasionally, animals develop more extensive regional reactions. These more
Minimum Database and Diagnostics
Identification of insect stings is not difficult if human caretakers were with the animal. Accurate diagnosis of Hymenoptera stings stems from a history of potential contact with stinging insects and the clinical signs displayed by the victim. It has been reported that certain dog breeds (bull terriers, Staffordshire terriers, and boxers) have a higher incidence of severe reactions to insect stings.15
The circumstances surrounding the sting episode may reveal clues as to the offending insect.
Treatment
For most solitary stings the application of ice, cool compresses, and antihistamines is sufficient to halt swelling and to ease discomfort. The majority of small local reactions to honeybee and wasp stings resolve completely without treatment within a few hours. On account of their dense coats, time-consuming and meticulous searches for and removal of embedded stingers should not be attempted. Vespids do not leave stingers behind. Honeybee venom sacs continue to contract even after the stinging
Prevention and Prognosis
Bees are attracted to dark colors and strong fragrances. Mammalian sweat seems to agitate them, attacks can be triggered by CO2 from the victim’s breath, and they are defensively stimulated by dark colors.11 Avoiding areas with flowering plants where bees are feasting on nectar and keeping outdoor eating areas and garbage cans clean (because wasps are attracted to food waste) lowers an animal’s risk of being stung. Avoid scented shampoos and soaps for your dog. Truly an ounce of prevention is
Gross and Histologic Lesions
The behavior or bees and wasps can help predict their stinging probability. Histopathological lesions following simple, single, nonreactive local stings are either absent, undetectable, extremely mild, or nonspecific. Even after fatal anaphylaxis, there are no pathognomonic findings on necropsy and pathological changes are very general.1, 7 In necropsy after suspected fatal anaphylactic reactions, particular attention must be paid to the larynx for the presence of hyperemia, edema, and
Differential Diagnoses
Because the initial stinging incident is rarely witnessed, and the clinical signs can be notoriously nonspecific, a diagnosis of insect sting can be easily missed by both owners and clinicians. A correct diagnosis depends on a high index of suspicion for possible insect stings, presenting clinical signs, and attempts to understand the conditions surrounding the episode. A list of differential diagnoses and potential look-alikes for insect stings is included in Table 4.
Fire Ant
Reports of fire ant stings are becoming more widespread. Fire ants are members of the order Hymenoptera, family Formicidae, subfamily Myrmicinae and genus Solenopsis. There are native fire ants in the United States, but two imported species Solenopsis richteri (the black imported fire ant) and Solenopsis invicta (the red imported fire ant) are of major medical importance.11 The black imported fire ant (S. richteri) is originally from eastern Argentina and Uruguay.22 The red imported fire ant (
Lethal Dose
Imported fire ants represent a significant health hazard for people and animals living in endemic areas. Sting reactions range from local pustules to anaphylaxis. Anaphylaxis is the main cause of fatal response to fire ant stings. Anaphylactic reactions are not dose dependent and do not correlate with the number of stings.
Systemic toxic reactions to envenomations by fire ants have been reported after 50 to 100 simultaneous stings.7 Fatal toxic reactions have been reported in dogs and other
Toxicokinetics
The mechanism of toxicity of fire ant stings is fairly unique. Imported fire ant venom differs from the venoms of bees, wasps, and hornets, which are composed largely of protein-containing aqueous solutions. Fire ant venom is made up of 95% water-insoluble alkaloid.28 The alkaloid portion consists primarily of 2,6 di-substituted piperidines, which have cytotoxic, hemolytic, antibacterial, and insecticidal properties. The alkaloids produce sterile pustules, but do not induce the IgE response
Clinical Signs
Reactions to imported fire ant stings range from minor skin lesions to anaphylaxis and death. Typical stings cause an annoying burning sensation. Three types of local reactions may be present: a wheal and flare reaction, a sterile pustule, and a large regional reaction. Local reactions alone occur in nonallergic animals.
The typical local reaction to a sting, the wheal and flare, is followed by immediate pain, inflammation, and intense pruritis. The wheal and flare reaction usually resolves
Minimum Database and Confirmatory Tests
Definitively establishing that fire ants are the cause of particular lesions can be difficult. Helpful clinical clues in determining a diagnosis of fire ant stings include development of a classic pustule after 24 hours, actual identification of the stinging insect, and the presence of typical fire ant mounds in the vicinity of the stinging incident. There are no laboratory tests to determine fire ant exposure. Veterinary clinicians should familiarize themselves with stinging insects found in
Treatment
Currently no treatment has been shown to be beneficial in preventing or resolving location reactions, including the characteristic pustules. However, various therapies may provide symptomatic relief. Local sting reactions may benefit from antihistamines, topical corticosteroids, application of cool compresses (water or alcohol), ice, and topical treatment with camphor and menthol (Sarna lotion). Topical lidocaine preparations have also been suggested. Some dogs stung by fire ants appear to feel
Prevention and Prognosis
Currently there are no effective insect repellants to protect companion animals from fire ants. Reaction to imported fire ant stings is best prevented by avoidance. Yards, exercise areas, and playing fields, must be routinely inspected for the presence of ant mounds. Many attempts have been made to eradicate fire ants from an area, but none have been shown to be completely successful. Basic methods currently used are broadcast applications of toxic baits that are carried back to the mound by
Gross and Histologic Lesions
The intense inflammatory response and pustule that develops at the fire ant sting site has been shown to result from potent cytotoxins and hemolytics found in the alkaloid venom fraction. These toxins cause localized necrosis of the dermis and underlying connective tissue that creates the characteristic sterile pustule that develops within 24 hours of most stings.28 In the continental United States, the pustule is only caused by imported fire ant stings. An erythematous flare follows the sting
Differential Diagnosis
Potential differential diagnoses and possible look-alikes to imported fire ant stings are listed in Table 7. These include any conditions leading to immediate swelling, pain, and pruritis. Differential diagnoses include trauma, infection, neoplasia, allergy, self-trauma, or other causes of anaphylaxis.
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