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Home arrow Economics arrow American Trypanosomiasis Chagas Disease, Second Edition: One Hundred Years of Research

Eclectic species

Some species of triatomines are adapted to specialist niches, but many others are generalists, more eclectic, and may be a danger to humans by transmitting Chagas disease. These species, classified as secondary, are a concern because the strictly domesticated species of vectors have been targeted for extermination through various regional initiatives fighting Chagas disease in most endemic countries. In more general terms, in many areas the problem is made worse by wild species of triato- mines now playing a role in transmission. This transmission relates to sylvatic zoonotic foci and generally results in sporadic occurrences of human cases. However, these regions must be under entomological supervision because an increased risk of contact between humans and infected vectors might emerge from uncontrolled environmental factors. T. brasiliensis is now considered the most important Chagas disease vector in the semiarid zones of northeastern Brazil. In a study on domiciliary

infestation from 1993 to 1999, 21 triatomine species were captured within the geographic range of T. brasiliensis in Brazil, but the highest domiciliary infestation rate was for T. brasiliensis.42 In the Brazilian Caatinga region, reinfestation by T. brasiliensis occurred after treatments of habitats. Based on genetic markers and population genetics, there appeared to be a triatomine flow (T. brasiliensis) between the neighboring sylvatic and artificial environments, such that the peridomestic area was a main interface function43 and the elimination of T. brasiliensis was more complex. Lastly, for the first time, a study reported the capture of T. brasiliensis in a sylvatic environment, using light traps, indicating that T. brasiliensis is attracted by light and that the colonization of houses might also be due to artificial light sources.44 In Mexico, Meccus longipennis, a species first identified in domiciles and peridomiciles, mostly in Jalisco State, is a truly wild species that colonizes artificial structures such as rock pile boundary walls separating crop fields45 and natural structures such as the common cliff and rock formations in the region.46,47 Surprisingly, two different vector dynamic models of this species could operate in the villages. In the first village studied, there was a high peridomestic colonization with one-third of the visited structures infested by M. longipennis4,8,49; in this case the triatomine entering the home could originate from peridomicile colonies. In the second village, the peridomicile colonization by M. longipennis was much lower and the triatomines entering the home probably originated from the wild50; most remarkable was the high proportion of M. longipennis males collected by the inhabitants in this village. This could explain the very low colonization load of the peri- domicile, whereas peridomestic structures offered to colonization were highly abundant, such as in the first village.

Among the unexpected species, Triatoma tibiamaculata, which is often associated with P. megistus and T. sordida, was found inside houses in Sad Paulo State, Brazil. The triatomines captured within the domiciles were mostly adults, but about half of them had fed upon humans.51,52 Further south on the west coast of Brazil in the state of Santa Catalina (municipality of Navegantes), an outbreak of acute human cases occurred in 2005 because humans had ingested sugar cane juice contaminated by the feces of triatomines. This was the first report involving T. tibiamaculata in peridomestic areas.53 In an area 1630 km further north, in the state of San Salvador, the main habitat of T. tibiamaculata is marsupial and rodent nests in bromeliads; in this area, it was suspected that T. tibiamaculata was transmitting Chagas disease.54 Similarly, in a periurban zone in Santiago, Chile, a study on the prevalence of blood sources in Mepraia spinolai (regarded as a syl- vatic species) identified several human feeding sources. This suggests that the wild insect might become a vector of greater epidemiological importance.55 Various entomological studies highlight complex situations where several triato- mine species coexist in environments neighboring developed areas, and many of these species are capable of entering dwellings. In communities in the northeastern province of Corrientes, Argentina, several species were identified in domestic ecotopes. T. infestans was the most dominant species. The second most dominant species was T. sordida, which is widely distributed in South America and most frequently found in extradomiciliary ecotopes. Although it is rarely domiciliated,

it could be considered capable of colonizing human dwellings.56 In the same province, a study showed a remarkable rate of infestation by T. sordida of palm trees on a farm (96—100% of Butia yatay and Acrocomia aculeate, respectively). The use of fronds in walls and roofs can favor the passive transport of wild triatomines to the domestic environment, as has been reported for Rhodnius spp. in tropical forests.57 Although T. sordida has not been considered dangerous, in 1995 in the Velasco province, Bolivia, it was the only species that colonized houses, and some autochthonous cases of infection were detected.58 The case of palm trees (Livistona australis) infested with R. neglectus in a square opposite the church in the city of Monte Alto in Brazil, where public notifications of domiciliary invasions were made, should also be noted.59 In the United States, a country considered to be nonendemic, the transmission of Chagas disease may occur at a very low level, given that six autochthonous human cases have been detected.60 Interestingly, a study used geographical information system and survey analyses of Chagas infection patterns to predict the impact of an increase in temperature in the year 2030 on the geographical distribution of three triatomine species (Triatoma sanguisuga, T. lecticularia, and T. protracta) in the southern United States; the results indicated that there is a risk of Chagas disease emerging in this country61 (Fig. 22.2).

 
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