Triatoma infestans
Triatoma infestans is a heteropterous insect of the Reduviidae family. It is hematophagous and considered one of the vectors responsible for the transmission of Chagas disease. It is called jam (in Colombia), black bug (in Paraguay), vinchuca (in Argentina, Chile, Uruguay and Bolivia), b>chipo (in Venezuela), chirimacha (in Peru), chinchorro (in Ecuador), chinche besucona (Mexico), in addition to barbeiro palança, percevejo-do-sertão (Brazil), among other names that it shares with other triatomine species. This insect is mostly domiciled and peridomiciliated, which makes it a vector of epidemiological importance. The natural host of T. infestans has probably been the guinea pig for millions of years. In Peru, the guinea pig has been recognized as an important reservoir of Trypanosoma cruzi, the parasite that causes the disease, and the cause of a large number of T. infestans due to its widespread presence as a domestic animal. In Bolivia T. infestans outside the human home, associated with wild guinea pigs. However, it feeds mainly on behalf of man, and given its wide distribution and ability to adapt to living in residential and peri-domiciliary areas, this species is the main cause of infection cases.
Not to be confused with the bed bug, another hematophagous hemipteran belonging to the Cimicidae family, also vector Trypanosoma cruzi.
Distribution
T. infestans is an endemic species to the South American Cone, where there is active transmission of the Trypanosoma cruzi parasite, and where new cases of infection occur each year. The insect lives in dry and warm areas, mainly in Argentina, Chile, Uruguay, Paraguay, Bolivia, Peru, Ecuador, Colombia and Brazil. It is possible to find it in 70% of the Argentine territory, from the northern limit, to the province of Chubut, and 50% of the Bolivian territory, in the regions with a dry and warm climate. In the Cochabamba and Chuquisaca regions of Bolivia, the vinchuca is responsible for one of the highest prevalences in the American continent. These Bolivian regions are considered the place of origin and epicenter of dispersion of T. infestans.
It preferably inhabits houses in rural areas built with bare walls, unsmoothed thatched roofs, and a messy interior, and in places close to the home, such as the chicken coop and corrals. Occasionally, specimens of this insect can be found in neat, clean, plastered homes. This is due to two main causes: a) its inhabitants travel to endemic areas without surveillance of the vector and may inadvertently transport it in their luggage or clothing; and b) due to the accumulation of materials such as quebracho, firewood, etc., coming from those areas.
Features
Morphology
The bug has different shapes according to the stage of growth it is in, with a size that evolves from 2 mm to 2 cm or 3 cm in the adult state. It is brown in color, with a border of transversal bands that alternate in brown and light colors. The head is sharp with two slight protuberances that are the eyes; It has, like all insects, six legs and a pair of antennae. Its body is flat, but when it feeds its abdomen swells and its wings, which are normally folded, rise up.
Life Cycle
Triatomines are hemimetabolous exopterygotes. The insect reproduces by eggs, which measure 2 to 3 mm, white in color, which change to pink when the evolution of the embryo is complete. From hatching to adulthood (winged forms), the bug goes through five growth stages (nymphal stages), with gradual changes in size and without wings. Each change consists of a molting process where the insect loses its exoskeleton to generate a new one, according to its new size. The nymphs, like the adults, are blood-sucking. From the egg stage to the adult stage, the evolutionary cycle of this insect can vary from eight months to a year. From the adult stage, the life of this insect lasts between one and two years.
Physiology and Behavior
The bug can thrive in areas with cold temperatures. Despite being an insect of warm climates and due to its domiciliary habits, the most propitious environment for its development is the home. Therefore, the warmth of the rooms favors their survival.
It is not common to see it during daylight hours since it is an insect with nocturnal habits, preferably after midnight and during the early morning, for which it has specialized vision. During daylight hours the vinchuca remains hidden.
The resistance to fasting of this insect is very high. The fifth instar nymph (pre-adult stage) supports more than 6 months of fasting. It is said that in certain cases, it eats other parasitic insects, such as fleas.
Like Rhodnius prolixus, T. infestans serves as a model for countless physiological and behavioral studies, due to its ease of breeding.
Chagas disease
Chagas disease occurs in the most impoverished areas of Latin America. It includes various components: the parasite, as responsible for the pathology; the vector, which is nothing other than the insect (the so-called Triatomines); and the host, which can be any mammal, including humans. The vinchucas' habitat has to meet certain conditions, such as houses with cracks in the walls, thatched or mud roofs, where they generally nest.
There are more than a hundred species of bugs, although those with epidemiological importance can basically be reduced to four. In Argentina, the so-called T. infestans.
Transmission of Chagas disease to humans
One of the characteristics of this insect is that it does not deposit the parasite in human tissue, but rather, when it bites a person and sucks blood, generally from areas close to the mouth such as the lips, its intestine swells and it forces it to defecate, depositing parasites on its victim's skin. Due to itching, people scratch, and they themselves incorporate the parasite into the tissues through this action. This vector transmission model was prevalent throughout Latin America until the 1980s.
Control
Studies have been carried out to try to eliminate the vector of domiciles and peridomiciles in rural areas in northern Argentina. The use of insecticides has momentarily decreased the number of triatomines, since the peridomiciliary structures, mainly those associated with the chicken farm, act as residual foci for the reinfestation of T. infestans. The low efficacy of the insecticides used has been attributed to the lack of ovicidal action, and the degradation and washing of the insecticides used, as well as the presence of a large number of possible hosts in domestic animals. In turn, pyrethroids they generate changes in the biological cycles of the bugs and make them resistant to them, making the control strategy very inefficient.
Image gallery
Detail of eggs already hatched
First stages of development T. infestans
Ninfa de Triatoma infestans feeding.
Vinchuga eye detail
Adult, dorsal view
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