Home Economics American Trypanosomiasis Chagas Disease, Second Edition: One Hundred Years of Research
Globalization of transmission
The increasing mobility of populations and the migration toward nonendemic countries have extended the infection to these countries through blood transfusion, organ transplantation, and the congenital form among migrants. The risk is related with the country of origin of the migrants and the rate of prevalence in that given country.
However, the advances observed in control of the transmission indicate that this potential extension to Europe, the United States, and Canada might be transitory or decreasing.
The World Health Organization recently launched the Global Network for Chagas disease elimination (WHO Global Network for Chagas Elimination— GNChE) to meet this situation.
Local epidemiological situations
There are a number of situations that depend of localized circumstances that have implications for vector control operations in the following areas:
The Chaco region
In spite of the sustained regular activities of vector control in this territory that is shared by Argentina, Bolivia, and Paraguay, the rates of infestation by T. infestans remain high. The reasons are associated to the complex peridomiciles of the rural houses, the emergence of resistance of the vector to the pyrethroid insecticides in the Provinces of La Rioja and Salta in Argentina and the Departments of Tarija and Cochabamba in Bolivia, and the presence of sylvan foci of T. infestans in Bolivia.
An integrated approach is being proposed that includes the improvement of peridomiciles and the use of higher doses of insecticide in these peridomiciles.76
Areas with vectorial transmission without intradomicile colonization
In these areas the transmission occurs because of the “visit” of the vector to the houses from the natural ecotopes to feed on the inhabitants after which the insect comes out. This form of transmission has been documented for R. pallescens in Panama and Colombia where the natural ecotopes of this species are several types of palm trees which are planted around the rural dwellings. The infection rates of this insect with the parasite are very high.
The surveillance and control in these particular situations are based on the analysis of variables that influence transmission such as the ratio houses/ecotopes, the insect infection rates by T. cruzi, the vulnerability of the dwelling to the insect “visit” and the frequency of these “visits.”77
Several alternatives of control have been proposed including physical or chemical barriers and the use of light sources that are not attractive to the insects.
Chemical vector control in the peridomicile
The peridomicile comprises the annexes, fences, corrals, and poultry yards that are built around the rural dwellings. The efficacy of the insecticides sprayed in this part of the house is low due to the degradation of the active principle by the rains and the continued exposure to sunlight. Other reasons of this low efficacy include the operational difficulties for spraying and the lack of order and cleanness in these spaces. So, residual infestations are invariably situated in the peridomicile.
It seems that the only alternative is the physical management of these spaces including reordering of the structures and the objects found there.
Resistance of vector populations to insecticides
“Control failures” that evidence the cross-resistance of vectors to pyrethroids have been documented in areas of Tarija and Cochabamba in Bolivia and in Salta and La Rioja in Argentina. Some field tests have been carried out with other insecticides such as carbamates and phosforates with poor results. It is necessary to develop and test new molecules to overcome the emerging resistance.
Low sensitivity of entomological methods
The available methods for direct detection of domiciled triatomines have a low sensitivity especially in circumstances where the insect densities are low as it is the case in advanced control phases. The direct reporting by the inhabitants of the presence of domiciled vectors is more effective and there are studies to evaluate the efficacy of traps with and without attractants such as pheromones.
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