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

New technologies for vector control

Suspension concentrate formulations of synthetic pyrethroid insecticides were the basic tool that allowed the successful elimination of domestic triatomines over

several Latino American regions. In the Southern Cone countries of South America, the area affected by T. infestans was reduced by over 90%. The success in the elimination of the domestic infestation contrasts with the difficulty of obtaining the same result in vast areas of the arid Gran Chaco. This difficulty comes from the low efficacy of the residual spray of current suspension concentrate formulations over the peridomestic structures (goat corrals, chicken nests, deposits, etc.). The low efficacy is caused by the rapid degradation of the active ingredient, as shown in several studies.58

A number of studies evaluated two different ways of using chemical control (xenointoxication, microencapsulated formulations) and one nonchemical control intervention alternatives (environmental management) to overcome the limitation of the low-efficacy pyrethroid formulations when applied to peridomestic structures. The idea of xenointoxication was to lay the active ingredient not over all the house unit (domestic and peridomestic structures), but only over the domestic vertebrate hosts of T. infestans. A series of articles by Amelotti and colleagues36-39 showed that current pour-on formulations already registered in Argentina for veterinary use produced high T. infestans mortality when applied on chickens during 45 days, but lower and shorter mortality when applied on goats. A pour-on formulation of fipro- nil produced low mortality during 15 days when applied on dogs. Similar positive and negative results on xenointoxication using pyrethroids and fipronil were also obtained.8,41,42 The second different approach to chemical control was to lay the active ingredient over the house unit, but with a formulation that protects the active ingredient inside a polymeric microcapsule. This formulation showed longer lasting effect than the traditional suspension concentrate formulation, under both experi-

mental32 and field conditions.33,59

The nonchemical control evaluated under the arid Chaco conditions was environmental management, changing the structure and construction materials of the goat corrals. By doing this with the participation of the productive community, the corrals that had been highly infested with abundant T. infestans populations, showed decreased infestation prevalence and vector abundance, as well as offering a substrate surface that improved the efficacy of the suspension concentrate pyrethroid formulations and improving the goat productivity, through 15% increased goat fecundity + decreased calf mortality + shorter calf development time.35

A different intervention type, using insecticidal paints based on organophosphate compounds, was applied to domestic and peridomestic structures in southern localities of Santa Cruz in Bolivia (intervention applied to over 2000 houses), where T. infestans is resistant to pyrethroids. In this case, houses show no infestation by T. infestans, either intradomestic or peridomestic populations, even 3 years after the application of the insecticidal paint.31,33

A number of recent published studies has shown the usefulness of mobile phone technology applied for vector surveillance and control, particularly malaria.60 A few projects testing the support that computer and information technology within the context of Chagas disease control were carried out during the last decade. A project coordinated from the University of Cordoba by 2009 developed an application for hand held devices to collect data on household inhabitants during the routine visits of primary health-care workers.61 After completing the round, data was downloaded into a desktop computer installed in the regional hospital, connected to a data server. The project confronted a number of technical problems, but was able to show the potentiality of the approach. One session was enough to train the field personnel of the primary health-care system on the use of the technology. Data collected through the application showed the distribution of infected children and pregnant women over an endemic area of Cordoba province (central Argentina). A comparison of two groups followed with the use of the application or not, showed that data from the group studied using the mobile application was better covered and patient follow up was higher than data collected from the group studied without the mobile application. The popularization of mobile phones using high level operative systems (i.e., Android) and the improvement of the communication infrastructure make easier than a few years back the implementation of a surveillance system over vector control, infection detection and treatment. Unfortunately, in spite of the advantages shown for the disease surveillance and control, the technology was never inserted within the health system of the Cordoba province.

Unpublished results of a public—private collaboration in Argentina (CRILAR- VARSTAT) explored the feasibility of developing a citizen information system for vector detection based on the combined use of SMS sent from mobile phones, through emails, or online forms. The development used the advances of the information system of the vector control programs installed in some provinces (e.g., La Rioja), that identified individually an recorded the geographic coordinates of all houses located in the endemic area (about 12,000 in La Rioja). Using a nonsmartphone to inform the house code number or a smartphone with GPS about the potential presence of triatomine vectors in the house was shown a perfectly feasible within the area with improved infrastructure of mobile communications (for the SMS management). In areas outside the mobile communication grid, the system could use synchronically or asynchronically the network of millions of personal netbooks that were distributed to primary and secondary school children through a federal funded program. The system could not only receive text data, but also pictures of the insects. The data could be received by a server installed in a federal and/or provincial health office that would eventually trigger a request the entomological evaluation of the house by the local health agency and carry out an IRS would the infestation by a domestic colony was confirmed. Technically, this development could be scaled up, provided there is the political commitment to fund and sustain such development. More importantly perhaps, is the need to organize and sustain a local health system that is alert and capable of responding promptly to such a request of a house infestation event, either to carry out the evaluation and eventually the vector control intervention.

At the national level, national programs of Chagas disease control have been trying to implement information systems to help improve the evaluation of the disease control activities. The case of Chile is the only example of a working information system for the vector control component, that provides regularly updated information to evaluate the ongoing activities. The system currently offers public access detailed public access information (based on an information transparency law) of house by house infestation by T. infestans and Mepraia spinolai and vector control interventions. Although the technical solutions and local knowledge are in place, no Chagas disease control program in Latin America was able to install such an information system. In spite of the very important advances made in the control of Chagas disease during the last decades, the road still to be traveled is probably the hardest. Although we have better knowledge and technical facilities than decades before, the lack of political commitment refrain further advances.

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