Complementary paths to Chagas disease elimination: the impact of combining vector control with aetiological treatment
Background: The World Health Organization’s 2020 goals for Chagas disease are: (1) interrupting vector- borne intra-domiciliary transmission, and (2) having all infected people under care in endemic countries. Insecticide spraying has proved efficacious for reaching the first goal, but active transmission remains in several regions. For the second, treatment has mostly been restricted to recently infected patients, who comprise only a small proportion of all infected individuals. The current fraction of people in endemic areas that has access to screening and treatment amounts only to c. 1%.
Methods: We extended our previous dynamic transmission model to simulate a domestic Chagas disease transmission cycle (with human and reservoir hosts and triatomine vectors), and used the model to examine the effects of both vector control (through indoor residual spraying of insecticides, IRS) and aetiological treatment of those infected with Trypanosoma cruzi, on achieving one of the operational criteria proposed by the Pan American Health Organization for intra-domiciliary, vectorial transmission interruption (i.e., reaching <2% seroprevalence in children <5 years of age). A range of endemicity levels (from low endemicity to very high endemicity) was simulated by increasing the carrying capacity of the domiciliated vectors. An external force of infection was included to account for the contribution of sylvatic
transmission.
Results: Depending on the level of endemicity, an antivectorial (IRS) intervention that decreases vector density by 90% annually would achieve the transmission interruption criterion in 2-3 years (low endemicity) to >30 years (very high endemicity). When this strategy is combined with annual aetiological treatment (leading to parasitological cure) in 10% of the infected human population, the seroprevalence criterion would be achieved in 1 year (low endemicity) or 11 years (high endemicity).
Conclusions: Combining highly effective vector control with aetiological (trypanocidal) treatment in humans would substantially reduce time to transmission interruption as well as infection incidence and prevalence (in human, reservoir and vector populations). However, the success of vector control may depend, among other things, on prevailing vector species, and many technical issues surrounding the application of insecticide to human dwellings. It will also be crucial to improve the coverage of screening programmes of the human population, the performance of the diagnostic tests to detect and confirm Chagas disease, the proportion of people treated, and the efficacy of trypanocidal drugs. While screening and access to treatment can be incremented as part of strengthening the health systems response, improving diagnostics performance and drug efficacy will require strong commitment and investment in research and development (R&D) of novel diagnostic and therapeutic tools.