Home Economics American Trypanosomiasis Chagas Disease, Second Edition: One Hundred Years of Research
Insect vectors associated with the human habitats
T. infestans is the T. cruzi vector with the widest distribution in South America, occupying the geographic regions that today belong to Argentina, Bolivia, Brazil, Chile, Paraguay, Uruguay, and southern Peru, usually found in rural dwellings inside the cracks of walls and roofs.
In the 1970s and 1980s, surveys of poorly constructed houses were carried out in endemic areas. In northern Chile, houses were inspected to determine whether they contained living vectors of Chagas disease. About one-third housed the vector, and a fifth of these insects were infected with T. cruzi. All of the houses inspected in some endemic areas of Argentina contained the vector. Between one-fourth and one-half of domestic animals (such as Guinea pigs, cats, and dogs) were found to be infected.27 Not unexpectedly, humans living in these areas were also commonly infected. About 40—80% of rural Bolivians were shown to be infected; infection was also detected in northern Chile (20%), southern Peru (12—20%), and endemic areas of Venezuela (54%).28,29
As a result, this domiciliated insect has been targeted for vector control activities in the past decade and has been eliminated from Chile, Uruguay, and Brazil, as well as large areas of Argentina and Paraguay.
T. infestans reaches high population densities in human dwellings, maintaining similarly sized populations from year to year. Its generation time is about 6 months, so it is possible to have two generations per year. Unlike other medically important insects such as mosquitoes, triatomines tend to adapt to efficiently exploit a stable environment like the nest of a mammal or a human habitation.
These insects were undoubtedly present in the human environment in preColombian times and effectively transmitted T. cruzi as we will see. The dispersion of the vectors is a high risk factor for human settlements. Historical reconstructions suggest that the dispersal of T. infestans from its supposed origin in central Bolivia was associated with documented human migration.30
This also is true for R. prolixus, the primary domiciliated-vector in regions of Colombia, Venezuela, and the vast majority of Central American countries. The development of R. prolixus from egg to adult takes 3—4 months whereas for species such as Triatoma dimidiata, a peridomiciliary/domiciliary species, this may take 1—2 years.
Triatomines show a high degree of dispersion, which involves two different mechanisms: (1) passive, by the vertebrate host and (2) active by walking or in the
Figure 2.2 Distribution of different triatomine species restricted to particular geoecoepidemiological factors.
case of adult insects flying. Several authors have reported the passive transport of triatomines in clothing, baggage, and transport and even the transport of eggs and nymphs in the feathers of birds.31
The geographic distribution of triatomine species extends from the Neotropics to Neoarctic regions and is closely related to environmental and ecological factors (Fig. 2.2).
Historical data indicate that the disease was transmitted in South America and seriously affected the inhabitants of endemic regions, who referred to the insects with vernacular names. The many indigenous names for the insect vectors such as vinchuca, hita, and chirimacha demonstrate the frequency with which pre-Colombian civilizations encountered these insects.
The Quechua word vinchuca, for example, means “bug that lets itself fall” which describes the behavior of domiciliated insect after feeding on blood. Hita is also a Quechua word that means “bedbug” and the chirimacha meaning is “which fears the cold.” These Quechua words clearly evoke the domiciliated behavior of triatomines.
Quechua (“qheshwa”) is an indigenous language of the Andean region, spoken today by approximately 13 million people in Bolivia, Peru, Ecuador, Northern Chile, Argentina, and Southern Colombia. It was the official language of Tawantinsuyu, the Inca Empire, which was the largest empire in pre-Colombian America. The administrative, political, and military center of the empire was located in Cusco in modern day Peru. The Inca civilization arose in the highlands of Peru sometime in the early 13th century (Table 2.1).
Table 2.1 List of the vernacular names for triatomine insects in South American geographical areas and cultures
Table 2.1 (Continued)
aQuechua, a native American language family spoken primarily in the Andes of South America, derived from an
original common ancestor language, Proto-Quechua. It is the most widely spoken language family of the indigenous
peoples of the Americas.
dKogui language, Colombia.
fAzteca (Nahuatl) language.
Source: Adapted, modified, and expanded from Schofield CJ, Galvao C. Classification evolution and species groups within the Triatominae. Acta Trop 2009; 110:88—100.32
|< Prev||CONTENTS||Next >|