Kiss & Tell

Kissing bugs belong to the insect family Reduviidae and are important public health pests because they transmit the causative agent of Chagas’ disease primarily in Mexico, Central America and South America. Many, but not all, kissing bugs belong to the genus Triatoma. These blood-sucking pests also occur in the southern half of the United States, but are most prevalent in states bordering Mexico. In addition to disease transmission, Triatoma bites have been known for more than 100 years to cause allergic reactions.

Although much less is known about insect bite allergy than sting allergy, insect bites also may be an important cause of severe allergic reactions and even anaphylaxis. Allergic reactions have been reported following many different types of insect bites, primarily Triatoma bugs, horse and deer flies and mosquitoes. Several different Triatoma species are present in the United States, but allergic reactions are reported most commonly from the western states. Because the Triatoma bite usually is painless and inflicted during sleep, the person may not be aware of the bite, and resulting allergic reactions may not be diagnosed or mistakenly attributed to other causes.

UNWANTED AFFECTION. These insects are called kissing bugs because of the nasty habit of sucking blood on the face, often near the lips. This is a misnomer because the bugs will take a blood meal from any area of exposed skin — legs, arms, hands, etc. There are at least 10 Triatoma species found in the United States, but only about six of these are commonly encountered. Allergic reactions have been reported after bites by five species (T. protracta, T. gerstaeckeri, T. sanguisuga, T. rubida and T. rubrofasciata). Studies have shown that T. protracta and T. rubida are the species most often reported to cause allergic reactions in California and Arizona, respectively.

KISSING BUG BIOLOGY. Triatoma bugs feed on blood meals of vertebrate hosts, such as bats, other small- and medium-sized mammals, birds and humans. Kissing bugs have an egg stage, five nymphal stages and an adult stage. All stages of nymphs and both sexes of adults require a blood meal to survive. Most species complete development in five to 12 months, depending on temperature and availability of blood meals. The pests often are found in association with their host nests or caves, rodent burrows or human houses. For example, T. protracta often are found in wood-rat nests. Bugs periodically fly away from the nests of their hosts in nocturnal cyclical flights and may be attracted to lights at dwellings, subsequently gain entrance and try to feed. Species that are able to colonize homes usually do so in substandard structures with cracks and crevices, mud walls, thatch roofs and the like.

Kissing bug species found in Mexico, Central America and South America live in cracks and crevices inside homes and feed on human inhabitants at will. Since kissing bugs are nocturnal insects, they seldom are observed during daylight hours. Feeding occurs almost exclusively at night and may take more than a half hour to complete. Adults are capable of ingesting two to four times their body weight in blood. During or soon after feeding, the bugs begin to defecate, voiding excess water, uric acid and hemoglobin from the undigested portion of the previous blood meal on the skin and into the wound of the host.

REACTIONS TO TRIATOMA BITES. Kissing bug bites typically occur at night, on uncovered skin and usually are painless. Most people experience no reaction at all. Although bites by most species are not usually noticed, they leave a small hole (punctum) without significant surrounding redness. Several types of local reactions have been reported from the bites, including puncti, papules, small fluid-filled blisters and hives. The exact nationwide prevalence and incidence of kissing bug allergy are unknown. Although kissing bugs are found throughout a large area of the United States, allergy to Triatoma bites is more commonly reported in the West and Southwest.

Whether this is due to species differences in allergenicity, heavier infestation, increased numbers of human bites, reporting bias or other factors is unknown. Although all reports of allergic reactions to kissing bugs to date have been to Triatoma species, other members of the kissing bug subfamily have potential to produce allergic bite reactions.

Incidence of Triatoma allergy in a few areas has been determined to be quite high. In one area of Santa Barbara County, Calif., the prevalence of Triatoma allergy among 120 local inhabitants was found to be 6.7 percent. As the human population continues to expand into Triatoma habitat, allergic reactions to Triatoma bites may become a more common problem. Anaphylactic reactions from kissing bug bites typically awaken the patient from sleep with itching, burning or difficulty breathing, all of which are typical symptoms of anaphylaxis. Gastrointestinal symptoms such as nausea, vomiting, diarrhea or abdominal cramps also may occur. As in all severe allergic reactions, prompt medical attention is needed since anaphylactic shock may be fatal.

CHAGAS’ DISEASE. Although uncommon in the United States, Chagas’ disease is the most serious worldwide human health problem posed by kissing bugs. The agent of Chagas’ disease, Trypanosoma cruzi, lives in the intestinal tract of the bugs. Several species of Triatoma defecate during or shortly after feeding and deposit the parasite on the host’s skin. The parasite invades the host’s skin when the skin is damaged due to scratching. Chagas’ disease begins as an acute illness with fever, swollen and painful lymph glands, heart dysfunction and possibly encephalitis-like symptoms. Survivors of the initial phase, which carries a mortality of 2 percent to 10 percent, generally enter a non-symptomatic phase. This phase may last for 10 to 20 years before serious heart muscle problems develop. There currently is no effective treatment for Chagas’ disease.

Although North American species of Triatoma have tested positive for T. cruzi, Chagas’ disease is uncommon in the United States. The low incidence of the disease in the United States may be due to less virulent Trypanosoma species, a lower density of Triatoma species in this country, or the 20- to 30-minute delay in defecation after feeding noted in North American Triatoma species. Interestingly, recent surveys of blood bank samples have revealed that dozens of cases of Chagas’ disease may be occurring in the U.S., but remain undiagnosed. Stay tuned.

PROTECTION AND CONTROL. Protection against Triatoma bites involves personal protection measures and environmental sanitation. Personal protection measures from kissing bugs involve avoidance where possible and the use of pesticides approved for indoor use. For instance, sleeping in adobe or thatched-roof huts in endemic areas should be avoided, and bed nets should be used when this is not possible. Domestic or peridomestic kissing bug species (Mexico, Central America and South America) may be controlled by proper construction of houses, sensible selection of building materials, sealing of cracks and crevices and precision targeting of insecticides within the home.

In the U.S., prevention of bug entry into homes may involve outdoor light management. Lights should be placed away from the house and shine back toward it, instead of being attached directly to the house. PCOs also should seal entry points around the home. Examination of blankets and sheets to make sure that no Triatoma are present and removal of piles of paper, clothing and other clutter from the bedrooms may reduce hiding places. Wearing thick pajamas with long legs and sleeves may help prevent bites. Nests of natural hosts (primarily rodents) around the home also should be eliminated to reduce the kissing bug population.

The author is a medical entomologist for the Mississippi Department of Health, Jackson, Miss.