A Field Trial of Alternative Targeted Screening Strategies for Chagas Disease in Arequipa, Peru

In the wake of emerging T. cruzi infection in children of periurban Arequipa, Peru, we conducted a prospective field trial to evaluate alternative targeted screening strategies for Chagas disease across the city. Using insect vector data that is routinely collected during Ministry of Health insecticide application campaigns in 3 periurban districts of Arequipa, we separated into 4 categories those households with 1) infected vectors; 2) high vector densities; 3) low vector densities; and 4) no vectors. Residents of all infected-vector households and a random sample of those in the other 3 categories were invited for serological screening for T. cruzi infection. Subsequently, all residents of households within a 15-meter radius of detected seropositive individuals were invited to be screened in a ring case-detection scheme. Of 923 participants, 21 (2.28%) were seropositive. There were no significant differences in prevalence across the 4 screening strategies, indicating that household entomologic factors alone could not predict the risk of infection. Indeed, the most predictive variable of infection was the number of years a person lived in a location with triatomine insects. Therefore, a simple residence history questionnaire may be a useful screening tool in large, diverse urban environments with emerging Chagas disease

Host-seeking behavior and dispersal of <em>Triatoma infestans</em>, a vector of Chagas disease, under semi-field conditions.

International audienceChagas disease affects millions of people in Latin America. The control of this vector-borne disease focuses on halting transmission by reducing or eliminating insect vector populations. Most transmission of Trypanosoma cruzi, the causative agent of Chagas disease, involves insects living within or very close to households and feeding mostly on domestic animals. As animal hosts can be intermittently present it is important to understand how host availability can modify transmission risk to humans and to characterize the host-seeking dispersal of triatomine vectors on a very fine scale. We used a semi-field system with motion-detection cameras to characterize the dispersal of Triatoma infestans, and compare the behavior of vector populations in the constant presence of hosts (guinea pigs), and after the removal of the hosts. The emigration rate - net insect population decline in original refuge - following host removal was on average 19.7% of insects per 10 days compared to 10.2% in constant host populations (p = 0.029). However, dispersal of T. infestans occurred in both directions, towards and away from the initial location of the hosts. The majority of insects that moved towards the original location of guinea pigs remained there for 4 weeks. Oviposition and mortality were observed and analyzed in the context of insect dispersal, but only mortality was higher in the group where animal hosts were removed (p-value <0.01). We discuss different survival strategies associated with the observed behavior and its implications for vector control. Removing domestic animals in infested areas increases vector dispersal from the first day of host removal. The implications of these patterns of vector dispersal in a field setting are not yet known but could result in movement towards human rooms

Diagram (not to scale) of experimental design for each glass tank.

<p>Video cameras recording each area of the tank (A); primary (B) and secondary (C) refuges; glass-walled maze (D); and guinea pig cage (E). Green dots represent triatomine insects in the primary refuge (R1); red dots represent triatomine insects in the secondary refuge (R2); black dots represent triatomine insects in or under the guinea pig cage (Q1); and grey dots represent no triatomine insects. Q2, Q3, and Q4 stand for quadrants 2, 3, and 4.</p

Data from: Population structure of the Chagas disease vector, Triatoma infestans, at the urban-rural interface

The increasing rate of biological invasions resulting from human transport or human-mediated changes to the environment have had devastating ecologic and public health consequences. The kissing bug, Triatoma infestans, has dispersed through the Peruvian city of Arequipa. The biological invasion of this insect has resulted in a public health crisis, putting thousands of residents of this city at risk of infection by Trypanosoma cruzi and subsequent development of Chagas disease. Here we show that populations of Tria. infestans in geographically distinct districts within and around this urban center share a common recent evolutionary history although current gene flow is restricted even between proximal sites. The population structure among the Tria. infestans in different districts is not correlated with the geographic distance between districts. These data suggest that migration among the districts is mediated by factors beyond the short-range migratory capabilities of Tria. Infestans and that human movement has played a significant role in the structuring of the Tria. infestans population in the region. Rapid urbanization across southern South America will continue to create suitable environments for Tria. infestans and knowledge of its urban dispersal patterns may play a fundamental role in mitigating human disease risk

Observed and predicted number eggs as a function of time.

<p>Predictions based on outputs from Poisson model with random intercept and random slope.</p

Observed and predicted number of triatomine insects as a function of time.

<p>White symbols represent control group and black symbols represent intervention group. Symbol shapes differentiate between repetitions.</p

Distribution of triatomine insects on tanks over time in one of the three repetitions.

<p>Distribution of triatomine insects on tanks over time in one of the three repetitions.</p

Comparison of Poisson regression models to assess the emigration rate.

<p>Comparison of Poisson regression models to assess the emigration rate.</p

Activity level estimated by count of motion-activated snapshots.

<p>Graph shows count of moves recorded in one repetition. The inset shows a detailed histogram of moves during days and nights.</p

Median daily temperature and relative humidity across repetitions.

<p>Median daily temperature and relative humidity across repetitions.</p