Introduction

Kissing bugs are a potential health hazard,¹ particularly in the southwestern United States (US), where in the foothills surrounding the cities of Tucson and Phoenix, AZ, and San Diego, CA, numerous homeowners are bitten each year. In some cases, bites lead to allergic reactions,^2,3 including anaphylaxis, the most grave of allergic reactions. Two deaths are attributable to anaphylaxis following kissing bug bites.^4,5 Most kissing bug entries into homes in the Southwest are short-lived and do not lead to the permanent residence of the bugs in the home. In this report, we will use the terminologies of Noireau and Dujardin⁶ regarding the presence of kissing bugs in houses, namely, (1) intrusion, implying the accidental entrance into homes of usually adult kissing bugs attracted by lights or by passive carriage (other life stages of the bugs are not present); (2) domiciliation, where adults, nymphs, eggs, and exuviae are found in the home representing a tentative adaptation to the house; and finally (3) domestication, which includes domiciliation but with a larger geographic distribution as opposed to just a local phenomenon. A comprehensive collection of publications regarding intrusions and, in some cases, domiciliation in US houses has been published.⁷ Most of the descriptions are decades old and involve older home constructions. After uncovering domiciliation in one community in the Southwest, we prepared this report to provide a contemporaneous account of the breadth of kissing bug activity in this one community and other US homes.

The absence of domestication as defined earlier is advanced as one explanation for the paucity of autochthonous human Chagas disease in the US.⁴ Generally, newer homes in the US have concrete foundations, solid walls and ceilings, window screens, tight thresholds for windows and doors, and energy efficient measures for the use of air conditioning. In endemic areas of Chagas disease in Central and South America, many houses still have thatch roofs, no foundations, adobe brick or wattle and daub wall construction, and open doors and windows without screens, providing numerous points of entry and refugia for kissing bugs. In one community in Arizona, where domiciliation of homes by kissing bugs appears to be common, the homes have wooden foundations erected over rocky terrain, are advanced in age with numerous points of entry into the house for insects, and are invaded by Triatoma recurva, the largest and least studied of kissing bugs in the US.

Methods

Results

Bites

Typically, the reports of kissing bug bites in Tucson, AZ, begin in late May and extended to August. This time period corresponds with the increasing desert floor temperatures.¹ In 2015, there were 10 calls to the Arizona Poison and Drug Information Center concerning kissing bug bites. Six callers submitted bugs implicated in the bites: one Triatoma protracta, male; four Triatoma rubida, females; and one T. rubida, 2nd instar (T. rubida is the most commonly encountered kissing bug in the Tucson area). Of the 10 callers, the average age of the bite victims was 63 years (range, 30-88 years) and 70% of the victims were females and 90% were Caucasian. The characteristics of the homes and reactions to bites are provided in Table 1.

Table 1

Characteristics of victims and their homes.

Examples of domiciliation by kissing bugs

Apartment complex in Tucson, AZ

A woman in her 70s lived with two cats in the foothills of the Catalina Mountains in Tucson, AZ, in a newly constructed retirement village. Over the course of several months (June through August of 2013), she experienced numerous bites from kissing bugs usually after retiring to her bedroom. She collected and stored the bugs. All the bugs were T. rubida (Table 2).

Table 2

Kissing bugs captured in an apartment residence with evidence of domiciliation.

The first adult was captured in early June, and the last was captured in early July. Several immature instars were captured from late July to early August. She suffered four bites during the period of infestation. Large welts were formed on the skin adjacent to the bite sites and were very pruritic. She treated these with calamine lotion. Her apartment was sprayed by a pest control company in the first week of June, early on in the infestation. The apartment building was <10 years of age and had central air conditioning. The apartment was part of entire complex of buildings in the foothills of a mountain. Decorative native plants surrounded the complex. One side of her apartment was elevated two stories above the desert with established growths of cholla and prickly pear cacti that likely served as den sites for pack rats (Neotoma albigula), a favored host of T. rubida and T. protracta in the Southwest. The entrance was on the ground floor of a long, dark covered corridor with lights outside of each of the entrance doors kept on 24 hours a day.

Single dwelling, Palm Springs, CA

A woman in her 60s and her husband lived in a recently constructed ranch house in Palm Springs with adjoining desert acreage. They had no pets. She was bitten numerous times by kissing bugs while sleeping. Her husband was not bitten but slept in the same bed. In July, she finally searched the bedroom diligently and found one female and four 2nd instar nymphs of T. protracta between the mattress and box springs on her side of the bed. After removal of the bugs, there were no further bites and no further insects were discovered.

Single dwelling, Bisbee, AZ

A man in his 60s and his wife lived in a single dwelling home on the side of a sparsely populated canyon for >20 years. Each year in late June and July, he noticed the presence of kissing bugs (T. recurva) in his home. Over the years, he was bitten several times with only slight pruritus at the bite sites. His house is entirely made of wood (floors, ceilings, and walls). The wooden beams upon which the first floor rests are directly atop large, irregular rock outcroppings. (This is a characteristic feature of most single, freestanding homes in the community.) There are screens on the windows, but no air conditioning. The couple has no pets. For seven years, the owner has been collecting kissing bugs in the home and sending them to the authors for identification. Four years ago, he constructed a bedroom about 100 feet from his infested house. It is also surrounded by rocky projections. The foundation is concrete, and the walls are concrete block with stucco wall surfaces. He has never seen a kissing bug in this building in contrast to his longtime home that continues to be infested. He collects on an average 30 T. recurva per year in the house, mostly adults and some nymphs, particularly 4th and 5th instars. Another resident in the canyon (in her 70s) has also been collecting kissing bugs from her home for the same period of time. Her home, like the previous one, is entirely made of wood, with a wood foundation resting directly on the soil and rock outcroppings. She typically collects more bugs (perhaps 30-60 per year, sometimes with a preponderance of 4th and 5th instars). All bugs collected are T. recurva. She has one dog living with her who is also bitten.

Single dwelling, city center of Bisbee, AZ

One woman in her 60s lives in a single dwelling house within the central part of Bisbee. The house was constructed decades ago, which has a wood frame with concrete floors and stucco walls. There is little space between the front of the house and the street and it is entirely given over to a rock garden. The streets near the home are steep and demarcated by rock walls, offering numerous refugia for insects. The homeowner routinely finds adult T. recurva in her home and on the retaining walls along the streets. The entrance doors to her home are several inches from the threshold, and the windows and doors are not occlusive, although screens are present. She typically collects 15-30 T. recurva each year in her home, both nymphs and adults. She has no pets and claims to have been bitten over a hundred times in the years she has resided in Bisbee. Her home is about half mile from the canyon homes described earlier. These observations demonstrate that the largest kissing bug in the US, T. recurva, lives freely within the city confines of Bisbee or flies from the surrounding mountains. T. recurva is known to fly perhaps a mile, or more, in the canyon environment.⁹

Discussion

This report documents the continuing problem of kissing bug bites, particularly in Southwest communities whose growth encroaches upon the habitat of the usual sylvan hosts of these bugs. Home intrusion by kissing bugs is for the most part a transient, seasonal occurrence. Only rarely is there domiciliation and usually in older homers with multiple entry sites lacking appropriate pest control measures. Domiciliation is occurring in Bisbee, AZ, and may be due to the terrain, upon which the homes are built, which is the natural habitat of T. recurva. A study of T. recurva performed in Sabino Canyon (similar in terrain to Bisbee) reported that T. recurva could fly perhaps a mile or more.⁹ Thus, it is possible that T. recurva is flying into the city center from surrounding canyons. T. rubida and T. protracta favor lower foothills and a more gravel/dirt terrain with plentiful pack rat nests. T. sanguisuga in southern Louisiana is usually found around the bodies of water; indeed, the most common blood source in the New Orleans bugs was frogs.¹⁰ This is quite different from T. sanguisuga found in drier Texas.¹¹

Home intrusion is usually accompanied by bites, some of which result in severe allergic reactions, such as anaphylaxis like the example given in this report. This cause of anaphylaxis is easily overlooked in busy ERs where physicians begin with the preconception that the life-threatening condition is due to drugs or foods. However, some victims are aware of being bitten and may bring in the kissing bug and the cause can be established. However, many people with anaphylaxis from kissing bug bites are unaware of being bitten, which occurs while they are sleeping. The clue to the problem resides in the history: victims arise from sleep with the abrupt onset of shortness of breath and whole body pruritus. It is evident from the data from the Arizona Poison and Drug Information Center that every patient experienced a local reaction to the bite and many experienced more troublesome symptoms, such as dizziness (40%) and breathing difficulty after the bite (20%); 30% of the victims sought medical care following the bite (Table 1). Many homeowners with kissing bug intrusions contracted with pest control services and experienced no recurrence of bites in the same season.

This report documents that house structure is important in preventing intrusion by kissing bugs in the US. The two examples of homes with kissing bug intrusion were older structures with many portals of entry for the bugs. The home in New Orleans Parish is instructive in several ways. The homeowners built a bedroom adjacent to the home with air conditioning and have experienced no bug intrusions into the bedroom. For some unknown reasons, only adult bugs have been found in this home. Domiciliation of kissing bugs occurred mostly in older homes with multiple portals of entry for the bugs. In the case of houses in Bisbee, AZ, many of the foundations were made of wood placed directly on large boulders. At one residence, the homeowners built a bedroom with air conditioning not far from the main house and sealing to minimize air loss has prevented the intrusion of bugs for years, whereas the main house remains a domicile for nymphal and adult kissing bugs. In Tucson where T. rubida is the most common kissing bug, domiciliation may follow intrusion by dispersing gravid female bugs that lay eggs inside the home within days of entry. The homes domiciliated in Bisbee, AZ, were occupied by T. recurva, the largest and least studied of US kissing bugs. At least 10 homes in one canyon community are occupied by kissing bugs every year, and the occupants of the houses sleep under mosquito netting year-round. The almost exclusive finding of T. recurva in Bisbee may be a clue to their preferred habitat of rocky canyon walls, and perhaps T. recurva may be more amenable to domiciliation than T. rubida, T. protracta, or T. sanguisuga.

The kissing bug species involved in this study harbor T. cruzi, but autochthonous cases of Chagas disease are extremely rare with seven documented cases to date.⁴ The rates of parasite carriage vary considerably. For example, in recent studies in Tucson, AZ, T. cruzi was found by polymerase chain reaction (PCR) in 25% of wild caught T. rubida (32/128 total bugs) and 35.3% of T. protracta (6/17)¹²; a study involving T. rubida captured in the home and peridomestic area showed a rate of carriage of T. cruzi of 41.5% (68/164).¹³ Kissing bugs captured from the home in New Orleans Parish where the homeowner was infected with Chagas disease demonstrated that 59.2% (29/49) harbored T. cruzi.¹⁰ Twenty-one of 49 bugs fed upon humans, and 8 (38.1%) of those feeding on humans harbored T. cruzi. Therefore, there is a risk for transmission of T. cruzi among these US bugs, although demonstration of infection is rare.

One factor thought to be important in the transmission of T. cruzi to humans is the rate of defecation after feeding (defecation index). This rate is low in bugs caught in Tucson and fed on living hosts.¹⁴ Another study claimed higher defecation rates, but the bugs were fed sodium-citrated blood.¹⁵ The anticoagulated blood may have affected the defecation rate. Although the carriage of T. cruzi is appreciable among US bugs, the type of housing appears to protect homeowners likely aided by a low defecation index among the bugs.¹⁶

Author Contributions

Conceived and designed: SAK, PLD, JOS. Analyzed the data: SAK, PLD, JOS. Wrote first draft: SAK. Contributed to writing: JOS, PLD, NB, SAK. Agree with results: SAK, FMS, KB, NLB, PLD, SS, JOS. Developed structure: JOS, PLD, SAK. Made critical revisions: JOS, SAK. All authors reviewed and approved of the final manuscript.