Stronger control-surveillance systems for vector-borne Chagas disease.

Abstract

The multinational initiatives for the control/surveillance of Chagas launched by disease-endemic countries and the Pan American Health Organization-World Health Organization (PAHO-WHO) contributed to control house-infesting triatomine-bug populations and to reduce disease incidence. However, after 30 years, Chagas disease (CD) transmission persists the Americas. In their recent review, Rojas de Arias et al.(1) highlight the ‘practical impossibility’ of interrupting vector-borne Trypanosoma cruzi transmission, due to the zoonotic nature of most transmission cycles, with well over 100 vector species widely spread across the Americas. Then, Rojas de Arias et al.(1) emphasise the need for stronger surveillance systems to monitor and control CD. Here, I will (1) briefly discuss the prospects for interrupting vector-borne T. cruzi transmission and (2) provide an overview of some innovative approaches that, I believe, can play important roles in the development and operation of stronger control-surveillance systems for vector-borne CD. Disease control needs clear goals, and those goals often heavily depend on the natural history, risk factors, transmission routes and dynamics, pathogenesis, and treatment of the disease. Eradication, elimination, reduction of incidence, reduction of the number of severe cases, and reduction of fatality rates are all possible goals of disease control programs. (2) The most ambitious goal is disease eradication the complete elimination of an infection, with no new cases recorded in the absence of control measures. Eradication is practically impossible for zoonoses such as CD, whose etiological agent can be transmitted by 150+ vector species and infects a wide range of wild vertebrate hosts from the USA to Patagonia.(3) Therefore, the objective of a CD control program cannot be eradication, at least in the Americas. The main goal of the multinational initiatives against CD was the elimination of the strongly synanthropic, non-native populations of a few “primary” vectors mainly Triatoma infestans and Rhodnius prolixus.(4) Elimination of R. prolixus from Mexico and some countries of Central America was certified in 2011 by PAHO/WHO, but R. prolixus-infested houses were detected in rural sites in Mexico after certification.(5) Moreover, a new record of T. infestans in Mexico was recorded after 50 years.(6) In Peru, non-native T. infestans populations were not controlled in Arequipa (see references in Rojas de Arias et al.(1)). In addition, T. infestans residual foci have been detected in Brazil after certification.(7) Overall, these data indicate that elimination of non-native populations of “primary” vectors is feasible, but has many challenges. Elimination may not be the best goal for native vectors of CD.(8,9) There is a high species richness of Triatominae in the Americas.(3) Moreover, it is important to highlight that the response of some native species to vector control with insecticides was not the same as that observed for non-native species. In Brazil, for example, insecticide spraying reduced dramatically T. infestans distribution, but no significant reduction in distribution was observed for most native species. Moreover, the interruption of chemical treatment was systematically followed by recolonisation of native species,(10) mainly in unplastered houses.(11) In the state of Bahia, there was a clear reduction in the distribution of T. infestans and an increase in the relative abundance and distribution of T. sordida and T. pseudomaculata after 40 years of the vectorcontrol program. The high frequency of native triatomine species invading houses in the Americas in recent years(7,12,13) highlights the need to reinforce entomological surveillance actions to prevent CD. WHO established goals for controlling CD by 2030, including the interruption of transmission through vectorial, transfusion, transplantation and congenital routes in many endemic countries.(14) Achieving those goals is feasible for non-vector-borne transmission,(15) but many challenges remain for vector-borne transmission. Thus, I agree with de Rojas Arias et al.(1) that the WHO 2030 goal of interrupting vector-borne transmission seems unfeasible because: (i) wild triatomine populations are widespread, (ii) surveillance methods for synanthropic triatomines are not perfect, and (iii) CD still has low visibility and priority. Thus, it is necessary to reinforce the surveillance of vector-borne transmission of CD. In the next paragraphs I will highlight some innovative strategies that could help strengthen this surveillance: (I) online training for health agents (II) development of apps to identify vectors and improve surveillance with community participation and citizen science, (III) vector-borne transmission-risk mapping.