Version May 2024
INTRODUCTION — Triatomine insects (colloquial names include kissing bug, Mexican bed bug, and cone-nosed bug) are found primarily in the western and southern United States, in Central and South America, and in Mexico (picture 1 and picture 2). These insects feed on blood and will bite various animals and people, although humans are not a primary host [1].
Triatoma bites are generally painless and asymptomatic. However, reactions can occur, ranging from local irritation at the site to allergic and anaphylactic reactions.
Triatomines are also of medical interest because they are the insect vectors for the protozoan Trypanosoma cruzi, which causes Chagas disease [2]. Triatoma and other closely related species found in the United States infrequently transmit T. cruzi, whereas the infection is endemic in some parts of South America. They do not transmit other human disease agents.
Local and allergic reactions to Triatoma bites are discussed in this topic review. Chagas disease and public health measures to control populations of kissing bugs in endemic areas are presented elsewhere. (See "Chagas disease: Epidemiology, screening, and prevention".)
EPIDEMIOLOGY OF TRIATOMA ALLERGY — Triatoma bites are among the most common causes of insect bite-related allergy and anaphylaxis [3]. However, anaphylaxis induced by bites is far less common than anaphylaxis induced by stings (eg, from Hymenoptera species such as bees, wasps, and ants). The prevalence of allergy to Triatoma bites has not been extensively studied. A survey study of one community in California found that 13 percent of the rural population self-reported allergic reactions to kissing bug bites [4].
Risk factors for exposure — Persons at risk for Triatoma bites are those living in poorly constructed houses in endemic areas, those sleeping with windows open at night, and people with homes situated in areas with an abundance of wild mammal hosts nearby, such as wood rats and other rodents, opossums, and armadillos.
In the United States, where homes are less easily penetrated, there is still evidence that Triatoma and humans regularly come into contact. In a study from California, 7 percent of the population possessed antibodies to Triatoma protracta salivary antigens, suggesting that they had been fed on by these insects [5]. A study of Triatoma captured in areas distant from human dwellings found that the majority of insects tested had recently ingested human blood [6].
ENTOMOLOGY OF TRIATOMA — Kissing bugs belong to the insect family Reduviidae (sometimes called reduviid bugs), subfamily Triatominae, and genus Triatoma (figure 1). Within the Triatominae subfamily, some (but not all) species are in the genus Triatoma. Thus, not all kissing bugs are genus Triatoma, and some non-Triatoma kissing bugs also may be vectors of Chagas disease.
Identification — Triatoma are winged insects that are approximately 1.3 to 2.5 cm long with flattened, shield-shaped bodies (picture 1 and picture 2). The head is elongated and sometimes cone shaped. They are various shades of brown or black, and some have prominent stripes of red, orange, or yellow color at the edges of the abdomen.
Worldwide distribution — Triatoma are primarily distributed throughout the western and southern United States, Central and South America, and in Mexico. Within the United States, there are at least 10 Triatoma species, but only about six of these are common (table 1) [7-9]. Most reports of allergic reactions to bites have originated in the southwest and west, primarily due to T. protracta [7,10]. Kissing bugs may rarely be found in the eastern or northern United States [11].
Habitat — Triatoma feed on blood from a variety of vertebrate hosts, such as rodents, opossums, other small and medium-sized mammals, birds, and humans [12]. They usually live with their animal hosts in rodent burrows, wood piles, or caves. As an example, T. protracta can frequently be found in wood rat nests.
Triatoma periodically fly away from their usual locations in nocturnal flights. During these flights, they may be attracted to porch lights on houses, and when daylight comes, they can crawl indoors through cracks around doors or windows in search of shelter from the sun and heat [13]. Once indoors, they may feed on pets and people.
In the United States, human interactions with Triatoma are considered to be incidental encounters. Triatoma do not easily enter modern homes, and when they do, there is usually one or a small number of insects per home. However, large infestations can occur in homes in developing countries that have cracks and crevices, mud walls, and thatched roofs [3,9,12,14]. (See 'Types of reactions' below.)
Biting behavior — Kissing bugs are active primarily at night and are rarely sighted during the day. In addition, feeding takes place almost exclusively at night. The name "kissing bugs" arose from the tendency of certain species to bite near the lips, but the bugs will bite any area of exposed skin. They generally will not bite through clothing or bed sheets.
Bites are typically multiple, ranging from 2 to 15 in a cluster on one part of the body, most commonly the hands, arms, feet, head, and trunk [15]. A full blood meal may take more than 30 minutes to complete, but the insect may be interrupted during this process and reinsert its proboscis several times in one area [13].
The lifecycle includes an egg stage, five nymphal stages, and an adult stage. Maturation takes 5 to 12 months, depending on availability of blood meals and temperature [9]. All stages of nymphs and both sexes of adults require blood meals to survive.
TYPES OF REACTIONS — Most people who are bitten by Triatoma have no adverse reaction and are usually unaware that they were bitten [16]. Triatoma bites most commonly leave a small, nonerythematous puncture in the skin [3,7,10,17]. However, the following reactions are possible:
●Local reactions caused by irritation from the bite or the debris left in the skin by the insect (see 'Local reactions' below)
●Allergic reactions, including anaphylaxis, caused by allergenic salivary proteins (see 'Allergic reactions' below)
Local reactions — Local reactions develop in some patients and may include the following [7,10,15,18]:
●Variable degrees of erythema and edema around the puncture sites (picture 3)
●Papules or vesicles around the bite, which may be grouped
●Hemorrhagic bullous lesions, usually on the hands and feet
Local reactions usually persist for days to one week. Delayed local reactions to bites may include urticarial or cellulitic lesions surrounding the bite site, which are sometimes associated with tender, swollen lymph nodes [15,19].
Differential diagnosis — Depending upon the type of local reaction, the differential diagnosis of Triatoma bites include herpes zoster, cutaneous infections, and other bites and stings.
●Herpes zoster – Local reactions that consist of grouped vesicles may be mistaken for herpes zoster, which presents as vesicles or vesicopustules with pain and surrounding edema and erythema. A dermatomal distribution can be an important distinguishing feature of herpes zoster. The clinical manifestations, culture, and serologic methods for diagnosing herpes zoster are presented separately. (See "Epidemiology, clinical manifestations, and diagnosis of herpes zoster" and "Diagnosis of varicella-zoster virus infection".)
●Allergic contact dermatitis – Poison ivy and poison oak and related plants can, on occasion, produce pruritic blistering reactions. These tend to be linear but not dermatomal.
●Infections – Staphylococcal and streptococcal infections, especially skin infections due to community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA), can begin with a single papule or pustule. Papules and pustules should be carefully unroofed and cultured if an infectious etiology is suspected. CA-MRSA occurs both sporadically and as institutional epidemics in nursing homes, prisons, military barracks, and athletic facilities. (See "Methicillin-resistant Staphylococcus aureus (MRSA) in adults: Epidemiology" and "Methicillin-resistant Staphylococcus aureus infections in children: Epidemiology and clinical spectrum", section on 'Epidemiology and risk factors'.)
●Other bites and stings – A variety of insects may sting or bite humans, including ants, fleas, bed bugs, ticks, mites (including those associated with scabies), mosquitoes, and biting flies (table 2) [20]. Some of these cause immediate pain, which does not occur with Triatoma bites. However, with the possible exception of some tick bites, identifying the insect inflicting the bite is of little clinical importance because local care is all that is required unless complications arise.
Treatment — Treatment of local reactions from kissing bug bites should be based upon symptoms, as there are no studies evaluating efficacy. Topical or oral antihistamines and topical corticosteroids may be helpful for itching and local irritation, respectively. Oral or parenteral antibiotics are prescribed if the lesion appears to be superinfected.
Allergic reactions — The bites of Triatoma have been recognized as a cause of allergic reactions for more than a century [21,22]. Not all species have been reported to cause allergic reactions, but at least five are regularly implicated (table 1) [14,20]:
●T. protracta (most often reported to cause allergic reactions in California) [5]
●Triatoma gerstaeckeri
●Triatoma sanguisuga
●Triatoma rubida (most often reported to cause allergic reactions in Arizona) [20]
●Triatoma rubrofasciata [22]
Signs and symptoms — Manifestations of allergic reactions and anaphylaxis to Triatoma bites may include itching, flushing, burning, urticaria, angioedema, wheezing, stridor, or hypotension. Gastrointestinal and abdominal symptoms may include nausea, vomiting, diarrhea, and abdominal cramping [3,10,14,20,23]. Vaginal bleeding was described in several cases [3,20], and it is not clear if this is a unique feature of Triatoma reactions or simply a reflection of uterine contractions, which can be seen with anaphylaxis of any cause (table 3).
Diagnosis — Allergic reactions and anaphylaxis to Triatoma bites are diagnosed clinically and should be suspected in a patient with consistent signs and symptoms (table 3). Anaphylaxis is defined as a serious allergic reaction that is rapid in onset and may cause death (table 4). It usually develops within a few minutes to two hours of exposure to the causative trigger. (See "Anaphylaxis: Acute diagnosis".)
A relatively unique feature of anaphylaxis from Triatoma bites is that symptoms characteristically awaken the patient from sleep [20]. This nocturnal presentation is rarely seen with other causes of anaphylaxis. (See 'Differential diagnosis' below.)
Treatment — Triatoma-induced anaphylaxis is treated identically to anaphylaxis from any other cause. The cornerstone of treatment is intramuscular epinephrine, as discussed in detail elsewhere. There is no "antivenom" or other specific antidote for Triatoma-induced anaphylactic reactions. (See "Anaphylaxis: Emergency treatment".)
Most patients survive, but a fatal case of anaphylaxis from a Triatoma bite on the leg was reported in a 54-year-old woman with no significant past medical history [24]. She awakened from sleep with pruritus and shortness of breath and was comatose by the time she reached the emergency department 30 minutes later.
Identification of the insect — The ability to locate and identify the insect is important for the diagnosis of a Triatoma bite as the cause of anaphylaxis. Since most patients do not know that they have been bitten, the only other clues implicating Triatoma are identification of a bite on physical examination and, in patients in endemic areas for Triatoma, nocturnal anaphylaxis (which is otherwise uncommon).
As soon as possible after the allergic reaction, the patient (or a family member/caregiver) should carefully search the location where the bite took place and try to retrieve the insect for identification. The engorged insect may be found in bedding, between mattresses, or in/under upholstered furniture. Help from a licensed pest management professional may be needed in this effort. Successful location of the insect as a result of a thorough search was accomplished in >95 percent of cases in one study [10,15,21].
In addition to definitive identification, finding the insect is important in preventing further bites. Even low populations of Triatoma may lead to multiple biting events through time. However, bloodsucking insects usually require a period of digestion after feeding, so additional bites from the same insect are less likely to occur immediately. (See 'Avoidance measures' below.)
Differential diagnosis — Mosquitoes, bed bugs, and various biting flies have also been implicated in rare cases of anaphylaxis [25-31]. Visual identification and knowledge of the insects that are endemic to the area are critical for distinguishing between bites of these different insects (table 2).
Anaphylaxis occurring in the middle of the night has also been reported in adults with allergy to red meats [32]. The responsible allergen is a carbohydrate, and this may underlie the delayed onset of these reactions, which occur three to six hours after ingestion. In contrast, most food-induced anaphylactic reactions are caused by allergy to proteins and occur within minutes to two hours of ingestion. (See "Allergy to meats" and "Clinical manifestations of food allergy: An overview".)
The evaluation of anaphylaxis of uncertain etiology is presented elsewhere. (See "Idiopathic anaphylaxis" and "Anaphylaxis: Confirming the diagnosis and determining the cause(s)", section on 'Testing for allergen cause(s)'.)
Long-term management of Triatoma allergy — Patients suspected of having a Triatoma allergy should be equipped with the following:
●Epinephrine for self-administration (preferably two or more autoinjectors)
●Educational material about Triatoma avoidance
●Referral to an allergist for evaluation to ensure that other possible causes of anaphylaxis have been considered and excluded, especially if the insect was not identified
Access to epinephrine — Any patient who has experienced anaphylaxis should have access to an epinephrine autoinjector in the future, as prompt administration of epinephrine is the most effective treatment for anaphylaxis. They should be advised to fill the prescription immediately. Patients should keep this medication at the bedside, as this is the most likely site of a repeat reaction. Several patient education topics concerning anaphylaxis and the proper use of epinephrine autoinjectors are available. (See 'Information for patients' below.)
Other interventions for patients with anaphylaxis include the completion of an anaphylaxis emergency action plan that can be carried with the patient and used to facilitate future treatment and some form of medical identification jewelry. These measures are reviewed elsewhere. (See "Anaphylaxis: Emergency treatment", section on 'Discharge care'.)
Patients should also be advised to keep a supply of oral antihistamines (such as diphenhydramine) available for treatment of mild allergic symptoms.
Referral — Referral to an allergy specialist is helpful to ensure all other possible causes of anaphylaxis have been considered and for ongoing education about training in effective use of an epinephrine autoinjector.
As mentioned previously, there are no commercial products available for use in diagnostic skin testing and immunotherapy [3,7]. This is true despite the identification of the causative allergens in salivary gland extracts from Triatoma in the 1980s [3,5,7,20,23,33]. Procalin, a member of the lipocalin family of proteins that also includes salivary allergens of other invertebrates and vertebrates, is a major allergen and has even been expressed recombinantly [34,35].
Experimental immunotherapy — There are no commercially available extracts for use in immunotherapy. However, immunotherapy with experimental Triatoma salivary gland extracts has been described in two reports:
●A patient allergic to T. protracta bites was treated with immunotherapy in 1982, which was considered partially successful because the reaction to a post-treatment challenge bite was milder than several reactions sustained prior to treatment [3].
●Another five patients with histories of systemic allergic reactions to bites and positive skin tests and radioimmunoassays to salivary gland extracts were given immunotherapy with the same material used for diagnosis [7]. When challenged with a T. protracta bite between 28 and 32 weeks into treatment, four of five patients had no reaction. The one remaining patient developed mild urticaria to a bite challenge at week 14 of immunotherapy but had no reaction when challenged again after 33 weeks of treatment. Thus, these early attempts were encouraging.
AVOIDANCE MEASURES — Physical avoidance measures include sealing cracks and crevices in the house to eliminate entry points for the insects. Stacks of wood or other materials should not be located near the house. Outdoor lights that are directed onto the exterior of homes should be turned to shine away from the house, so that the insects drawn to them are less likely to contact the building. Outdoor plantings near homes should be kept neatly trimmed to prevent nesting of wood rats and other natural hosts for Triatoma.
Bedrooms should be free of clutter on the floor, and bedding should not be allowed to touch the floor. Bed nets can be used, and long-sleeved and long-legged pajamas are suggested, since Triatoma rarely bite covered skin. Some recommend wearing insect repellent on the skin while sleeping in endemic areas.
Pesticide application — In areas of the world where Chagas disease is endemic, kissing bugs are controlled with pesticides for the purpose of reducing disease incidence. (See "Chagas disease: Epidemiology, screening, and prevention".)
In the United States, the Environmental Protection Agency (EPA) has stringent laws concerning pesticide use. Although many over-the-counter pesticides with questionable efficacy are available, control of kissing bugs is best performed by a licensed pest management professional using only EPA-registered products. The authors suggest consulting such a professional if Triatoma are present or suspected to be present in or near one's dwelling.
ADVICE ABOUT CHAGAS DISEASE AFTER A TRIATOMA BITE — The advice given to a patient who has sustained a triatomine bite depends upon where he/she was likely exposed and the likely extent of that exposure:
●In the United States, the risk of contracting T. cruzi infection from kissing bug bites is low. Only about 30 cases of local transmission from triatomine bite to human have been reported [36,37]. Thus, patients who have sustained bites do not routinely require follow-up or evaluation for T. cruzi infection.
●Among immigrants in the United States, there are an estimated 300,000 who are unknowingly infected with Chagas parasite, resulting in an estimated 30,000 to 45,000 cases of cardiomyopathy annually [38,39].
Most patients infected with T. cruzi by triatomine bites are asymptomatic during the acute stage of infection. In a minority of patients, acute infection may be associated with a persistent local reaction, a chagoma (swelling and local lymphadenopathy), or for bites involving the orbit (or perhaps, getting bug feces in the eye), Romaña's sign (persistent unilateral edema, conjunctivitis, and lymphadenopathy).
Patients with Romaña's sign should be reported to the local health department and/or the United States Centers for Disease Control and Prevention regarding diagnosis and treatment of acute Chagas disease (as well as evaluating entomologic specimens for evidence of disease carriage) [40]. (See "Chronic Chagas cardiomyopathy: Management and prognosis", section on 'Antitrypanosomal therapy'.)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Beyond the Basics topics (see "Patient education: Anaphylaxis symptoms and diagnosis (Beyond the Basics)" and "Patient education: Anaphylaxis treatment and prevention of recurrences (Beyond the Basics)" and "Patient education: Using an epinephrine autoinjector (Beyond the Basics)")
SUMMARY AND RECOMMENDATIONS
●Triatoma insects (colloquial names include kissing bug, Mexican bed bug, and cone-nosed bug) are found primarily in the western and southern United States, Central and South America, and Mexico (picture 1 and picture 2). (See 'Introduction' above.)
●Kissing bug bites are usually painless and undetected by the victim. However, these insects are of medical importance both because they can transmit the protozoan Trypanosoma cruzi, which causes Chagas disease, and also because people can develop life-threatening allergic reactions to their bites. (See 'Allergic reactions' above and "Chagas disease: Epidemiology, screening, and prevention".)
●Local reactions to Triatoma bites, most commonly consisting of erythema and edema around the puncture sites (picture 3), develop in some patients and are managed symptomatically. (See 'Local reactions' above.)
●Allergic reactions/anaphylaxis to Triatoma bites typically occur in the middle of the night, as Triatoma are nocturnal and bite while the victim sleeps. With the exception of this one distinguishing feature, the signs and symptoms of Triatoma anaphylaxis may be identical to those resulting from other triggers. Fatal and near-fatal cases of anaphylaxis have been reported. (See 'Allergic reactions' above.)
●Acute treatment of anaphylaxis following a Triatoma bite is identical to acute treatment of anaphylaxis of any etiology. Upon discharge, all patients with anaphylaxis should be equipped with an epinephrine autoinjector and an anaphylaxis emergency action plan to manage initial treatment of recurrent episodes. Epinephrine should be kept at the bedside in the future. (See "Anaphylaxis: Emergency treatment", section on 'Immediate management'.)
●Once a patient with anaphylaxis has been stabilized, the home (or relevant site) should be thoroughly searched for the blood-engorged insect as soon as possible. If necessary, pest management professionals may be called upon to aid in the inspection process. Identification of the insect is important for diagnosis because reagents for skin testing and laboratory diagnosis are not available. Proper insect identification can be obtained from a local college or university entomology department or the extension service at participating land-grant universities nationwide. (See 'Identification of the insect' above.)
●Patients should be given information about how to prevent future contact with Triatoma, including modifications of their homes, bedrooms, and surrounding environment. If kissing bugs are suspected to be present or found in the home, a pest management professional should be contacted. (See 'Avoidance measures' above.)
●Specific immunotherapy to reduce an allergic patient's sensitivity to Triatoma is not commercially available. Thus, avoidance and education about early recognition and treatment of recurrent allergic reactions is critical. (See 'Long-term management of Triatoma allergy' above.)
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