Modelling historical changes in the force-of-infection of Chagas disease to inform control and elimination programmes: application in Colombia

Abstract

BackgroundWHO's 2020 milestones for Chagas disease include having all endemic Latin American countries certified with no intradomiciliary Trypanosoma cruzi transmission, and infected patients under care. Evaluating the variation in historical exposure to infection is crucial for assessing progress and for understanding the priorities to achieve these milestones.MethodsFocusing on Colombia, all the available age-structured serological surveys (undertaken between 1995 and 2014) were searched and compiled. A total of 109 serosurveys were found, comprising 83 742 individuals from rural (indigenous and non-indigenous) and urban settings in 14 (out of 32) administrative units (departments). Estimates of the force-of-infection (FoI) were obtained by fitting and comparing three catalytic models using Bayesian methods to reconstruct temporal and spatial patterns over the course of three decades (between 1984 and 2014).ResultsSignificant downward changes in the FoI were identified over the course of the three decades, and in some specific locations the predicted current seroprevalence in children aged 0–5 years is <1%. However, pronounced heterogeneity exists within departments, especially between indigenous, rural and urban settings, with the former exhibiting the highest FoI (up to 66 new infections/1000 people susceptible/year). The FoI in most of the indigenous settings remain unchanged during the three decades investigated. Current prevalence in adults in these 15 departments varies between 10% and 90% depending on the dynamics of historical exposure.ConclusionsAssessing progress towards the control of Chagas disease requires quantifying the impact of historical exposure on current age-specific prevalence at subnational level. In Colombia, despite the evident progress, there is a marked heterogeneity indicating that in some areas the vector control interventions have not been effective, hindering the possibility of achieving interruption by 2020. A substantial burden of chronic cases remains even in locations where serological criteria for transmission interruption may have been achieved, therefore still demanding diagnosis and treatment interventions.

Force of infection of Middle East respiratory syndrome in dromedary camels in Kenya

“…There are a few possible reasons why this FOI analysis identified the oldest age group as having the highest risk of infection based on model AIC. Questions remain as to whether [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Furthermore, the oldest age group has a much larger age range than the others, and therefore represents a greater cumulative risk.…”

Complementary Paths to Chagas Disease Elimination: The Impact of Combining Vector Control With Etiological Treatment

“…There are limitations to this study. The failure to interrupt intradomiciliary vectorial T. cruzi transmission in the Americas is likely to be linked not only to a lack of systematic implementation of vector control—particularly in hard-to-reach populations such as rural and indigenous communities [ 5 ]—but also to the existence of other T. cruzi transmission cycles, such as the presence of sylvatic vector populations in close contact with humans, against which IRS is not as efficacious as with domestic transmission [ 26 ]. Vector control has been very efficacious in areas with exclusively domiciliated vectors, as is the case of Central American countries [ 13 ].…”

“…In the context of Chagas disease, the 2012 London Declaration and the World Health Organization (WHO) roadmap on Neglected Tropical Diseases proposed that by the year 2020, total interruption of intradomiciliary transmission in Latin America and provision of care to all infected patients should be achieved [ 4 ]. However, recent data suggest that antivectorial programs are not being sustained in all endemic countries or regions [ 5 ]. Furthermore, treatment coverage is as low as <1% of the infected population [ 6 ], and access to care remains limited in several countries [ 7 ].…”

“…Successful vector control campaigns have been carried out against the vector species Triatoma infestans in much of the South Cone of South America [ 12 ], and Rhodnius prolixus in Central America [ 13 ]. However, active intradomiciliary transmission still occurs in many endemic regions, particularly in hard-to-reach populations in isolated rural communities of Latin America [ 5 ].…”

How Modelling Can Enhance the Analysis of Imperfect Epidemic Data

“…Based on two age-stratified serological studies, Salje et al used these approaches to show that, over the past 60 years, four distinct chikungunya outbreaks occurred in the Philippines, each affecting about a quarter of the population [49]. Similarly, combining age-stratified data from over 100 serosurveys, Cucunubá et al used catalytic models to quantify the impact of the Chagas' disease control and elimination programme in Colombia during the past three decades [50]. The study showed that, while the force of infection dropped by up to 90% in urban settings, it remained constant in remote areas, highlighting major geographic variations in the impact of the programme.…”