Degradation of insecticides used for indoor spraying in malaria control and possible solutions

• Published in: Malaria Journal
• Main Authors: Massinga Pedro, Muiambo Herminio, Maity Arjun, Nhlapo Nontete S, Moyo Lumbidzani, Labuschagne Frederick JWJ, Focke Walter W, Sibanda Mthokozisi M, Crowther Nico AS, Coetzee Maureen, Brindley Gordon WA
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2011
• Subjects: Indoor residual spray; DDT; pyrethroid; carbamate; stabilization; Arctic medicine. Tropical medicine; RC955-962; Infectious and parasitic diseases; RC109-216; Arctic
• Online Access: https://doi.org/10.1186/1475-2875-10-307; https://doaj.org/article/f7d5962ceecb4585be16002c180664f9

Abstract Background The insecticide dichloro-diphenyl-trichloroethane (DDT) is widely used in indoor residual spraying (IRS) for malaria control owing to its longer residual efficacy in the field compared to other World Health Organization (WHO) alternatives. Suitable stabilization to render these alternative insecticides longer lasting could provide a less controversial and more acceptable and effective alternative insecticide formulations than DDT. Methods This study sought to investigate the reasons behind the often reported longer lasting behaviour of DDT by exposing all the WHO approved insecticides to high temperature, high humidity and ultra-violet light. Interactions between the insecticides and some mineral powders in the presence of an aqueous medium were also tested. Simple insecticidal paints were made using slurries of these mineral powders whilst some insecticides were dispersed into a conventional acrylic paint binder. These formulations were then spray painted on neat and manure coated mud plaques, representative of the material typically used in rural mud houses, at twice the upper limit of the WHO recommended dosage range. DDT was applied directly onto mud plaques at four times the WHO recommended concentration and on manure plaques at twice WHO recommended concentration. All plaques were subjected to accelerated ageing conditions of 40°C and a relative humidity of 90%. Results The pyrethroids insecticides outperformed the carbamates and DDT in the accelerated ageing tests. Thus UV exposure, high temperature oxidation and high humidity per se were ruled out as the main causes of failure of the alternative insecticides. Gas chromatography (GC) spectrograms showed that phosphogypsum stabilised the insecticides the most against alkaline degradation (i.e., hydrolysis). Bioassay testing showed that the period of efficacy of some of these formulations was comparable to that of DDT when sprayed on mud surfaces or cattle manure coated surfaces. Conclusions Bioassay experiments indicated that ...