Dermatology Online Journal

Kissing bugs (Triatoma) and the skin
Rick Vetter MS¹
Dermatology Online Journal 7(1):6

1. Department of Entomlogy, University of California Riverside

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Abstract

Kissing bugs (Family Reduviidae) can be the source of nocturnal dermatologic wounds in the mid to southern latitudes in the United States. The insects are obligate blood feeders and though the bites may be asymptomatic, a variety of dermatologic eruptions or death from anaphylaxis can result. The various dermatologic forms of the bite can be mistaken for herpes zoster, erythema multiforme and the ubiquitous catch-all diagnoses of "spider-bite."

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Figure 1
Paratriatoma hirsuta (family Hemiptera) identified by Rick Vetter, UCR Entomology. Collected in the Mojave Desert east of Indio.

Introduction

In true entomologic terminology, the word "bug" strictly refers only to the large order of insects (Hemiptera) which are characterized by having sucking mouthparts. Most hemipterans are familiar to us as plant feeders (leafhoppers, aphids, stinkbugs), however, the family Reduviidae consists of predatory and parasitic insects, one group of which are obligatory blood-feeders that seek out mammals for their meals. They are known by a variety of colloquial names (kissing bug, cone-nosed bug, Mexican bed bug, etc.) and can be a cause of dermatologic wounds. The assaults are usually nocturnal and reactions are due to salivary proteins.[1] The most common kissing bugs in the United States are in the genus Triatoma with the less common Paratriatoma found in the southwest.

Life cycle and biology

There are 16 species and 18 subspecies of Triatoma in the United States, distributed in the southern 2/3 of the country; additional related species and genera are common in Central and South America.[2] The kissing bug is dorso-ventrally flattened and is armed with a long, piercing proboscis. Although its mouthparts are only capable of sucking and there are no opposing structures capable of biting, its feeding wounds are still referred to as bites. Triatoma insects go through 5 molts before reaching maturity.[3] Their typical North American animal hosts include woodrats, opossum, raccoons and armadillos.[2,3] The insects are suspected to also feed off of many domestic pets and the wild animals that are abundant around human habitats. They are most often found in direct association with their animal host; for example, inside the large debris nests of pack rats. However, they are also capable of taking blood meals from humans. Because of their association with wild animal hosts, interactions with humans are more probable in areas that are surrounded by a natural environment in comparison to the disrupted landscaping of urban areas.

Medical significance

Triatoma are predominantly nocturnal and feed off of a sleeping person's exposed human body parts.[1] They will not feed through clothing, although they will feed through large-weave laboratory cloth.[4,5] Typically, they position themselves next to the recumbent human, rather than on top of the host, to feed with the proboscis being the only contacting body part. Subjects describe the bite of Triatoma as virtually painless with a slight tingling sensation.[1,5,6] In laboratory observations, the insects fed for 8 to 15 minutes on humans before repletion and interfeeding duration was typically 3 weeks.[6] However, the insects were able to survive 3 to 6 months between meals.[7] In a large experimental study exposing 464 test subjects to 4 species of Triatoma nymphs and adults, most subjects exhibited no reactions to reduviid feeding with the number of symptomatic subjects being minimal (pruritus 0-4.2%, edema 0-3.2%, erythema 0-6.9%) 0 to 72 hours postbite for the variety of insect species tested.[5] Ryckman attributes this low response to lack of prior exposure of subjects to Triatoma salivary antigens. However, Triatoma can cause severe wounds via exposure to its salivary compounds and death from anaphylaxis is possible.[8] Most sleeping victims are not aware of the insect's presence during feeding, although for the few hypersensitive victims, severe allergic reaction to the insect's salivary secretions is sufficient to awaken them.[4,9]

Human interactions with Triatoma are considered to be incidental encounters and not deliberate infestations as the insects are typically found singularly inside homes and not as multiple intruders. Of definitive diagnostic importance, the engorged culprit is often found when sought; all 45 Texas patients and 95% of 110 California patients were able to recover the offending Triatoma when the home was thoroughly searched.[1,4] The insect often sought shelter in and around bedding or under sofa cushions. This high frequency of detection should readily allow one to confirm or exclude the bite of this reduviid insect.

Dermatologic expression

For most victims, reaction to Triatoma feeding is unremarkable.[10] However, for a minority, significant dermatologic injury occurs. Clinical expression has been divided into 4 categories and is summarized from Shields and Walsh.[1,4] Typically, feeding wounds are multiple (2 to 15 in number), grouped, and most common on hands, arms, feet, head and trunk in that order.[1]

• Papular lesions are similar to insect bites but have non-specific lymphocytic infiltration atypical of insect bite. Grouped lesions are often misdiagnosed as herpes zoster.
• Small vesicles surround the bite within 2 to 3 cm, commonly seen on the arms. No definite central puncture mark but wound is erythematous with moderate edema. Concomitant wounds elsewhere on the body can help with the diagnosis. Shields and Walsh list a patient with a hemorrhagic bullous lesion on the thumb who also had small vesicles on the arms.
• Large urticarial-type lesions (10 to 16 cm diameter)are also seen. Puncture wound may or may not be visible and in many patients and the lesion is erythematous. Lymphangitis and lymphadenitis may be associated with this type of wound.
• The most severe bite reaction exhibits hemorrhagic nodular-to-bullous lesions, typically on the hands and feet. The multiple lesions might be confused with erythema multiforme, however, in Triatoma bite, they are usually unilateral in occurrence. This type of wound is often attributed to the catch-all term, "spider-bite." Lymphangitis and lymphadenitis may be associated with this type of wound also.

In addition, the triatomine bugs of Central and South America are vectors of Chagas' disease (trypanosomiasis) which is caused by the parasitic protozoan Trypanosoma cruzi.[1,10] The mechanism of infection from Chagas' disease is not via feeding but instead through contamination of the wound or other bodily portals by fecal material during or shortly after feeding. Although North American Triatoma species have tested positive for T. cruzi, Chagas' disease is much less of a concern in the U.S. because the North American Triatoma delay defecation until 20-30 minutes post-feeding. By this time, they are usually no longer in contact with the sleeping human.[1,10] Hence, vectoring of the protozoan is much less likely. Although T. cruzi is not difficult to find in both North American triatomine insects and their mammalian hosts (e.g., raccoons, opossums), the incidence of Chagas' disease in humans is extremely low, though in Central and South America, it is of genuine epidemiologic concern.[11] However, North Americans still need to be aware of the disease as infected immigrants enter the country and transmission has also occurred through blood transfusion.[11]

An extensive, annotated bibliography of the medical aspects of triatomine insects has been compiled. [8,12]

Acknowledgment

RE Ryckman supplied many references and made improvements on an earlier draft of the manuscript.

References

1. Shields TL, Walsh EN. "Kissing bug" bite. Arch Dermatol 1956; 74:14-21

2. Usinger RL The Triatominae of North and Central America and the West Indies and their public health significance. US Pub Health Service, Pub Health Bull 1944;288:1-81

3. Keh B. Cone-nosed bugs of California. Calif Vector Views 1956;3:47-49

4. Walsh JD, Jones JP, Jr. Public health significance of the cone-nosed bug, Triatoma protracta (Uhler), in the Sierra Nevada foothills of California. Calif Vector Views 1962;9:33-37

5. Ryckman RE. Dermatological reactions to the bites of four species of triatominae (Hemiptera: Reduviidae) and Cimex lectularius L. (Hemiptera: Cimicidae). Bull Soc Vector Ecol 1985;10:122-125

6. Wood SF. Reactions of man to the feeding of reduviid bugs. J Parasitol 1942;28:43-49

7. Ryckman RE. Recent observations of cannibalism in Triatoma (Hemiptera; Reduviidae). J Parasitol 1951;37:433-434

8. Ryckman RE, Bentley DG. Host reactions to bug bites (Hemiptera, Homoptera): a literature review and annotated bibliography, part II. Calif Vector Views 1979;26:25-49

9. Nichols N, Green TW. Allergic reactions to "kissing bug" bites. Calif Med 1963;98:267-268

10. Kirchhoff LV. American trypanosomiasis (Chagas' disease)--a tropical disease now in the United States. N Engl J Med 1993;329(9):639-44. PubMed

11. Pung OJ, Banks CW, Jones DN, Krissinger MW. Trypanosoma cruzi in wild raccoons, opossums, and triatomine bugs in southeast Georgia, U.S.A. J Parasitol 1995;81(2):324-6. PubMed

12. Ryckman RE. Host reactions to bug bites (Hemiptera, Homoptera): a literature review and annotated bibliography, part I. Calif Vector Views 1979;26:1-24

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