Triatomines/Kissing bugs

Members of the subfamily Triatominae, also named kissing bugs, due to their nocturnal feeding in the faces of sleeping humans, are of relevance for the transmission of the pathogenic agent of American trypanosomosis or Chagas disease, Trypanosoma cruzi.

General Aspects

Taxonomy

Members of the heteropteran family Reduviiidae are commonly called assassin bugs, because most species attack and feed on other insects. There are 22 subfamilies in this family, including Triatominae, kissing bugs, respectively. The subfamily Triatominae is divided into 5 tribes and 14 genera with 106 species already known only from the New World (despite other species in India, Southeast Asia and one in Africa).

Distribution

The New World triatomine species occur from just south of the Great Lakes region of the USA to southern Argentina, with all but a few species concentrated in subtropical and tropical regions.

Kissing bugs can be divided into three general habitat groups: sylvatic, peridomestic, and domestic. Sylvatic forms inhabit nests, burrows and natural hiding places. Peridomestic forms utilize domestic animals as hosts by living in chicken coops, stables, corrals, as well as rabbit and guinea pig houses. The domestic (domiciliary) species have colonized human habitations, where they depend on human or domestic animal blood as food source.

Veterinary and Medical Importance

All triatomines have the potential to transmit T. cruzi, the agent of Chagas disease. Of the 119 described triatomine species in total, about half have been shown to be vectors of Trypanosoma sp., and about a dozen of these are considered vectors of major epidemiological importance (Krinsky, 2002).

General Morphology

Overview

Triatomines range in length from 5 to 45 mm, with the majority of species falling between 20 to 28 mm. Most species are black or dark brown, often with contrasting patterns of yellow, orange or red. The head of an adult triatomine is constricted posteriorly, forming a distinct neck. The region in front of the eyes is cylindrical to conical, supporting the name ’cone-nosed’ bugs. For further key characteristics see e.g. Krinsky (2002).

As in all Hemiptera, triatomines undergo hemimetabolous development (egg, five nymphal instars, adult). Both sexes of adults and all nymphal instars require blood for their survival and development. The entire life cycle from egg to adult may be as short as 3 to 4 months, but more commonly takes 1 to 2 years.

Feeding Behavior

Activity Dynamics

Triatomines are generally secretive, hiding in cracks and crevices. Most species are nocturnal and actively seek blood from diurnal hosts that are resting and sleeping at night. Kissing bugs can survive for months without a blood meal. When hosts are available, they commonly feed every 4-9 days. As in other hematophageous arthropods, feeding behavior is initiated by a combination of physical and chemical factors. The amount of blood ingested depends on the duration of feeding, which again is governed by the presence of chemicals in the blood of the host and by stretch receptors in the abdomen of the bug. The time required to engorge fully varies from 3 to 30 min. After engorging, the bug removes the rostrum from the host and, in most species, defecates on or near the host before crawling away to seek shelter.

As T. cruzi is excreted by the bug during defecation, the interval between feeding and defecation is a major factor in determining the effectiveness of a species as vector of T. cruzi. The pathogen enters the host either via normal healthy mucosa or broken skin. Pruritic skin reactions following triatomine bites tend to enhance transmission of T. cruzi by stimulating the bitten host to scratch infective feces into the bite wound.

Host Spectrum

Triatomines transmit T. cruzi to a variety of domestic and wild animals. Depending on the strain of trypanosome, the species and age of the host infected and other poorly understood factors, the infection can lead to disease. Some 150 mammal species are susceptible to T. cruzi, with possible high prevalences in dogs, cats, rodents, and both domestic and wild lagomorphs, constituting an important reservoir for human infection.

Depending on the type of habitat (sylvatic, peridomestic, domestic) wild or domestic animals as well as humans are frequented by triatomines for blood feeding. Amphibians, lizards, opossums, rodents, armadillos, sloths and bats are some of the wild animals used as food source. Many of the so-called peridomestic species, as well as a few domestic ones, have maintained sylvatic adaptations and may migrate from wild hosts to domestic animals and humans, depending on the availability of suitable habitats and hosts.

Control

Control of kissing bugs is implying the use of insecticides and improving housing conditions.

References

• Krinsky, W.L.: True bugs (Hemiptera). In: Mullen, G., Durden,L. (eds.): Medical and Veterinary Entomology. 2002, Academic Press, London, pp. 67-86