NDLI: Indoor residual spraying practices against Triatoma infestans in the Bolivian Chaco: contributing factors to suboptimal insecticide delivery to treated households

Content Provider	Springer Nature : BioMed Central
Author	Gonçalves, Raquel Logan, Rhiannon A. E. Ismail, Hanafy M. Paine, Mark J. I. Bern, Caryn Courtenay, Orin
Abstract	Background Indoor residual spraying (IRS) of insecticides is a key method to reduce vector transmission of Trypanosoma cruzi, causing Chagas disease in a large part of South America. However, the successes of IRS in the Gran Chaco region straddling Bolivia, Argentina, and Paraguay, have not equalled those in other Southern Cone countries. Aims This study evaluated routine IRS practices and insecticide quality control in a typical endemic community in the Bolivian Chaco. Methods Alpha-cypermethrin active ingredient (a.i.) captured onto filter papers fitted to sprayed wall surfaces, and in prepared spray tank solutions, were measured using an adapted Insecticide Quantification Kit (IQK™) validated against HPLC quantification methods. The data were analysed by mixed-effects negative binomial regression models to examine the delivered insecticide a.i. concentrations on filter papers in relation to the sprayed wall heights, spray coverage rates (surface area / spray time [m2/min]), and observed/expected spray rate ratios. Variations between health workers and householders’ compliance to empty houses for IRS delivery were also evaluated. Sedimentation rates of alpha-cypermethrin a.i. post-mixing of prepared spray tanks were quantified in the laboratory. Results Substantial variations were observed in the alpha-cypermethrin a.i. concentrations delivered; only 10.4% (50/480) of filter papers and 8.8% (5/57) of houses received the target concentration of 50 mg ± 20% a.i./m2. The delivered concentrations were not related to those in the matched spray tank solutions. The sedimentation of alpha-cypermethrin a.i. in the surface solution of prepared spray tanks was rapid post-mixing, resulting in a linear 3.3% loss of a.i. content per minute and 49% loss after 15 min. Only 7.5% (6/80) of houses were sprayed at the WHO recommended rate of 19 m2/min (± 10%), whereas 77.5% (62/80) were sprayed at a lower than expected rate. The median a.i. concentration delivered to houses was not significantly associated with the observed spray coverage rate. Householder compliance did not significantly influence either the spray coverage rates or the median alpha-cypermethrin a.i. concentrations delivered to houses. Conclusions Suboptimal delivery of IRS is partially attributable to the insecticide physical characteristics and the need for revision of insecticide delivery methods, which includes training of IRS teams and community education to encourage compliance. The IQK™ is a necessary field-friendly tool to improve IRS quality and to facilitate health worker training and decision-making by Chagas disease vector control managers. Graphical Abstract
Related Links	https://parasitesandvectors.biomedcentral.com/counter/pdf/10.1186/s13071-021-04831-1.pdf
Ending Page	13
Page Count	13
Starting Page	1
File Format	HTM / HTML
ISSN	17563305
DOI	10.1186/s13071-021-04831-1
Journal	Parasites & Vectors
Issue Number	1
Volume Number	14
Language	English
Publisher	BioMed Central
Publisher Date	2021-06-16
Access Restriction	Open
Subject Keyword	Parasitology Entomology Tropical Medicine Infectious Diseases Veterinary Medicine Veterinary Science Virology Triatoma infestans Trypanosoma cruzi Chagas disease Vector control Diagnostic Indoor residual spraying Insecticide quantification Chaco Bolivia Veterinary Medicine/Veterinary Science
Content Type	Text
Resource Type	Article
Subject	Veterinary Infectious Diseases Parasitology
Journal Impact Factor	3/2023
5-Year Journal Impact Factor	3.3/2023

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