Triatominae

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Triatominae
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hemiptera
Family: Reduviidae
Subfamily: Triatominae
Jeannel, 1919
Tribes

Alberproseniini
Bolboderini
Cavernicolini
Linshcosteusinii
Rhodniini
Triatomini

The members of Triatominae /traɪ.əˈtɒmɨniː/, a subfamily of Reduviidae, are also known as conenose bugs, kissing bugs, assassin bugs, or triatomines. Most of the 130 or more species of this subfamily are haematophagous, i.e. feed on vertebrate blood; a very few species feed on other invertebrates (Sandoval et al. 2000, 2004). They are mainly found and widespread in the Americas, with a few species present in Asia, Africa, and Australia. These bugs usually share shelter with nesting vertebrates, from which they suck blood. In areas where Chagas disease occurs (from the southern United States to northern Argentina), all triatomine species are potential vectors of the Chagas disease parasite Trypanosoma cruzi, but only those species (such as Triatoma infestans and Rhodnius prolixus) that are well adapted to living with humans are considered important vectors.

History

At the beginning of the 19th century Charles Darwin made one of the first reports of the existence of triatomines in America in his Journal and Remarks, published in 1839 and commonly known as The Voyage of the Beagle. The following is an extract which he based on his journal entry dated 26 March 1835:[1]

"We crossed the Luxan, which is a river of considerable size, though its course towards the sea-coast is very imperfectly known. It is even doubtful whether, in passing over the plains, it is evaporated, or whether it forms a tributary of the Sauce or Colorado. We slept in the village, which is a small place surrounded by gardens, and forms the most southern part, that is cultivated, of the province of Mendoza; it is five leagues south of the capital. At night I experienced an attack (for it deserves no less a name) of the Benchuca (a species of Reduvius) the great black bug of the Pampas. It is most disgusting to feel soft wingless insects, about an inch long, crawling over one's body. Before sucking they are quite thin, but afterwards they become round and bloated with blood, and in this state are easily crushed. They are also found in the northern parts of Chile and in Peru. One which I caught at Iquique, was very empty. When placed on the table, and though surrounded by people, if a finger was presented, the bold insect would immediately draw its sucker, make a charge, and if allowed, draw blood. No pain was caused by the wound. It was curious to watch its body during the act of sucking, as it changed in less than ten minutes, from being as flat as a wafer to a globular form. This one feast, for which the benchuca was indebted to one of the officers, kept it fat during four whole months; but, after the first fortnight, the insect was quite ready to have another suck."[2]



Note: Luxan is Luján de Cuyo, the Benchuca is identified by Richard Keynes as Triatoma infestans which is nowadays commonly called the "Vinchuca" bug.[1]

There has been considerable medical speculation as to whether or not Darwin's contact with triatomines in Argentina was related to his later bouts of long term illness, though it is unlikely to have been caused on this specific occasion as he made no mention of the fever that usually follows the first infection.[1]

Discovery of triatomines relation with Chagas disease

In 1909 the Brazilian doctor Carlos Chagas discovered that these insects were responsible for the transmission of T. cruzi to many of his patients in Lassance, a village located on the banks of the São Francisco River in Minas Gerais (Brazil). Poor people living there complained of some insects they called barbeiros that bite during the night. Carlos Chagas put his first observations in words:
"Knowing the domiciliary habits of the insect, and its abundance in all the human habitations of the region, we immediately stayed on, interested in finding out the exact biology of the barbeiro, and the transmission of some parasite to man or to another vertebrate".
Another Brazilian, Herman Lent, former student of Carlos Chagas, became devoted to the research of the triatomines and together with Peter Wygodzinsky made a revision of the Triatominae, a summary of 40 years of studies on the triatomines up to 1989.[3]

Biological aspects

Rhodnius prolixus nymphs and adult

Life cycle

Triatomines undergo incomplete metamorphosis. A wingless first instar nymph hatches from an egg, about the size of the tip of a fork. It passes successively through 2nd, 3rd, 4th, and 5th instars. Finally, the fifth instar turns into an adult, acquiring two pairs of wings.

Ecology

All triatomine nymph instars and adults are haematophagous and require the stability of a sheltered environment where they aggregate. Most species are associated with wild nesting vertebrates and are named "sylvatic" triatomines. These live in ground burrows with rodents or armadillos, or in tree-dwellings with bats, birds, sloths, or opossums. Few species (5%) live in human dwellings or in the surroundings of human houses (peridomicile) in the shelters of domestic animals, these are named "domestic" species. Many sylvatic species are in process of domiciliation ("semidomestic").

Behavior

Most triatomines aggregate in refuges during day and search for blood during night when the host is asleep and the air is cooler. Odors as well as heat guide these insects to the host. Carbon dioxide emanating from breath, as well as ammonia, short chain amines and carboxylic acids from skin, hair, and exocrine glands from vertebrate animals, are among the volatiles that attract triatomines. Vision also serves triatomines for orientation. During night, adults of diverse species fly to houses attracted by light.

Adults produce a pungent odour (isobutyric acid) when disturbed, and are also capable of producing a particular sound by rubbing the rostrum over a stridulatory sulcus under its head (stridulation).

Epidemiology

Domestic and sylvatic species can carry the Chagas parasite to humans and wild mammals; birds are immune to the parasite. T. cruzi transmission is carried mainly from human to human by domestic kissing bugs; from the vertebrate to the bug by blood, and from the bug to the vertebrate by the insect's feces, and not by its saliva as occurs in most bloodsucking arthropod vectors such as Malaria mosquitoes.

Triatomine infestation especially affects older dwellings. One can recognize the presence of triatomines in a house by its feces, exuviae, eggs, and individuals themselves. Triatomines characteristically leave 2 kinds of feces like strikes on walls of infected houses; one is white with uric acid, the other is dark (black) containing heme. Whitish or pinkish eggs can be seen in wall crevices. After having had a blood meal the insects sometimes show a limited mobility and can be identified easily.

Tribes, genera and numbers of described species

The monophyletic nature of the Triatominae subfamily is strongly support by molecular data, indicating that their blood-sucking character has occurred only this once within the Reduviidae.[4]

Note: For a complete list of species see Galvão et al. (2004)

Most important vectors

All 138 Triatominae species are potentially able to transmit T. cruzi to humans but the following five species are the most epidemiologically important vectors of Chagas disease.

References

  1. ↑ 1.0 1.1 1.2 Keynes 2001, p. 315
  2. ↑ Darwin 1839, pp. 403–404
  3. ↑ http://digitallibrary.amnh.org/dspace/handle/2246/1282
  4. ↑ Weirauch, Christiane, and Munro, James B. (2009). "Molecular phylogeny of the assassin bugs (Hemiptera: Reduviidae), based on mitochondrial and nuclear ribosomal genes". Molecular Phylogenetics and Evolution 53 (1): 287–299. 
  • Brenner RR,Stoka AM (1987) Chagas’ disease vectors. I, II and III. CRC Press. Boca Ratón
  • Dujardin JP, Schofield CJ, Panzera F (2000) "Les vecteurs de la maladie de Chagas: recherches taxonomiques, biologiques et génétiques". Academie Royale des Sciences d'Ultre-Mer. Belgium.
  • Galvão C, Carcavallo R, da Silva Rorcha D, Jurberg J (2004) "A checklist of the current valid species of the subfamily Triatominae Jeannel, 1919 (Hemiptera, Reduviidae) and their geographical distribution, with nomenclatural and taxonomic notes". Zootaxa 202: 1-36 First pages
  • Lent H, Wygodzinsky P (1979) "Revision of the Triatominae (Hemiptera, Reduviidae), and their significance as vectors of Chagas disease". Bull Am Mus Nat Hist 163:123–520
  • Maldonado-Capriles, Jenaro (1990) "Systematic Catalogue of the Reduviidae of the World". Special Edition of the Caribbean Journal of Science. University of Puerto Rico, Mayaguez, Puerto Rico. 694 pp.
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  • Sandoval CM, Joya M, Gutiérrez M, Angulo VM (2000) Cleptohaematophagy of the Triatominae bug Belminus herreri. Med Vet Entomol 14(1):100-101
  • Schofield CJ (1994) Triatominae: biology & control. Eurocommunica Publications. West Sussex. UK 80 pp.
  • Schofield CJ (2000) "Biosystematics and evolution of the Triatominae". Cad. Saúde Pública. [online]. vol.16 suppl.2 [cited 6 May 2005], p. 89-92. ISSN 0102-311X. Available from World Wide Web.
  • Zeledón R (1981) El Triatoma dimidiata (Latreille, 1811) y su relación con la enfermedad de Chagas. Editorial Universidad Estatal a Distancia. Costa Rica
  • Zeledón R, Rabinovich (1981) "Chagas' disease: an ecological appraisal with special emphasis on its insect vectors". Annu Rev Entomol 26:101-33 Available from World Wide Web

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