The impact of landscape transformation on the reinfestation rates of Rhodnius prolixus in the Orinoco Region, Colombia.

Trypanosoma cruzi, the agent responsible for Chagas disease, is widely distributed in the Americas in association to insect vectors and animal reservoirs. Triatomines are common vectors of Chagas disease and they vary in their distribution and affinity to human or sylvatic environments. Thus, control programs that include house spraying have been successful in regions were insects have a tendency to domiciliation. In the Orinoco region of Colombia, Rhodnius prolixus is the main vector presenting a stable sylvatic cycle, but is also found colonizing human dwellings. In 1997, health authorities developed a control program in the Department of Casanare spreading with insecticide houses in 667 localities. Infestation Indexes (I.I.) were calculated at the locality level before and after spraying. Times for re-infestation assessment varied between 1 and 67 months. Localities were classified into 3 groups according to their I.I. after spraying. Group 1 dropped their I.I. down to zero, Group 2 had a drop but remained positive and Group 3 increased its I.I. after spraying. We classified each group in terms of their land use characteristics before and after spraying based on satellite images obtained for the years 1997 (beginning of the study) and 2002 (end of program). We found that spraying significantly reduce the I.I. on average. However, we found that time after spraying does not produce significant differences in the I.I. Interestingly, land use changes and variations on I.I. after spraying for all groups were significantly dependent.