Unexpected failures to control Chagas dosease vector with pyrethroid spraying in Northern Argentina

JUAN M. GUREVITZ; MARÍA SOL GASPE; GUSTAVO F. ENRÍQUEZ; CLAUDIA V. VASSENA,; JULIÁN A. ALVARADO-OTEGUI; YAEL M. PROVECHO; GASTÓN A MOUGABURE CUETO; MARÍA INÉS PICOLLO; URIEL KITRON; RICARDO E. GÜRTLER

JOURNAL OF MEDICAL ENTOMOLOGY

ENTOMOLOGICAL SOC AMER

Lugar: Lanham; Año: 2012 vol. 49 p. 1379 - 1386

0022-2585

Abstract The elimination efforts of Triatoma infestans (Klug) in South America through residual application of pyrethroid insecticides have achieved highly variable degrees of effectiveness in the Gran Chaco region. We investigated the origin of vector control failures after a standard community-wide spraying with suspension concentrate deltamethrin in a well-defined rural area in northeastern Argentina encompassing 353 houses. Insecticide spraying reduced house infestation much less than expected: from 49.5% at baseline to 12.3% and 6.7% at four and eight months postspraying, respectively. Persistent infestations were detected in 28.4% of houses infested before spraying, and numerous colonies with late-stage bugs were recorded after interventions. Parallel, blind laboratory bioassays showed reduced susceptibility to pyrethroids in local bug populations. Eleven of the 14 tested bug populations showed reduced mortality in diagnostic dose assays (range, 35±5% to 97±8%) whereas the remainder had 100% mortality. A fully-enclosed residual bug population in a large chicken coop survived four pyrethroid sprays, including a double-dose applications, and was finally suppressed with malathion. The estimated RR of this bug population was 7.17 (range, 4.47-11.50). Our detailed field data combined with laboratory bioassays and a residual foci experiment demonstrate that the initial failure in suppressing T. infestans was mainly due to the unexpected occurrence of reduced susceptibility to deltamethrin in an area last treated with pyrethroid insecticides 12 years earlier. Close monitoring of the impact of control actions provided early warning signals of vector control failures