Date Published: January 8, 2015
Publisher: Public Library of Science
Author(s): Ricardo Castillo-Neyra, Corentin M. Barbu, Renzo Salazar, Katty Borrini, Cesar Naquira, Michael Z. Levy, Eric Dumonteil. http://doi.org/10.1371/journal.pntd.0003433
Abstract: Chagas 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.
Partial Text: Chagas disease, a vector-borne disease caused by the parasite Trypanosoma cruzi, affects from 7 to 8 million people in the Americas . The vast majority of people infected are not detected , , and when the disease manifests clinically it cannot be reversed and can be fatal –. In addition to the inability to detect early cases and the lack of treatment in advanced stages, currently there are no vaccines available to prevent infection . Therefore, efforts to halt transmission are crucial to reduce the burden of disease .
Across the three repetitions, we observed a similar pattern of emigration of insects; the number of triatomine insects in the primary refuge decreased faster in the intervention tank than in the control tank (Figs. 2 and 3). We also observed that triatomine insects in the intervention tank leaving their primary refuge dispersed in both directions, towards and away from the empty guinea pig cage (Fig. 2). In the control tank the number of triatomine insects in the primary refuge reduced slightly over time and those triatomines that emigrated consistently did so towards the secondary refuge. Fig. 2 illustrates the dispersal data over time from one of the repetitions, although we observed the same pattern in all three repetitions. In this figure, the number of triatomine insects that were found in their primary refuge is represented by green dots, and insect emigration from the primary refuge is represented by the reduction of those dots over time. This reduction is more marked in the intervention tank. Emigration from the primary refuge to the secondary refuge was prevalent in both tanks and is represented by the red dots. However, in the intervention tank alone, some insects left their primary refuge and dispersed towards the empty guinea pig cage; this emigration is represented by the black dots.
Here we characterize the ex-situ dispersal of T. infestans after removal of sources of blood. The observed reduction of insect count in their primary refuge was, on average, 19.7% over 10 days, and triatomine insects did not distribute randomly over the available area. Some of the insects remained in the primary refuge (close to the guinea pig cage), some migrated to the secondary refuge (far from the guinea pig cage), and some dispersed towards the empty guinea pig cage. The empty guinea pig cage was the only source of olfactory cues associated with blood sources, and also offered shelter to bugs.