Field and laboratory evaluation of newly-introduced Long-lasting insecticide treated nets (llins) for malaria Vector control

Abstract

Insecticide treated nets (ITNs) have been proven to substantially reduce morbidity and mortality due to malaria among children and pregnant women in Sub-Sahara Africa. However, the disadvantages with ITNs are that they require regular re-treatments and users are restricted not to wash them. Recently, long lasting insecticide treated nets (LLINs) have been introduced to replace ITNs in malaria vector control programs, because manufacturers claim that LLINs do not require any further treatment once deployed. Currently, all malaria vector control programs funded by World Health Organization (WHO) recommend use of LLINs that meet their specification. The current study was undertaken to evaluate the efficacy, wash and physical durability of four newly WHO approved LLINs in a rural village of western Kenya. The study evaluated the optimal wash-drying regimens suitable for the above LLINs under tropical conditions and also compared local field washing methods to the WHO recommended procedure. The study evaluated feeding success and survival rates of vectors through repeatedly washed above LLINs under laboratory conditions and also compared side by side the physical durability of polyethylene and polyester based LLINs that are currently used in western Kenya. The statistical analyses were done in SAS using specific packages appropriate for each objective. The study found that in general nets which were washed and dried hanging under the shade retain~d more insecticide (62.5%) compared to nets which were dried spread on the ground in direct sunlight (56.3%). The study also found that there was a significant difference in insecticide loss between the four drying regimens and the three washing procedures p<O.OOOland p=O.OOl respectively. The vector feeding success and survival rates increased with increasing number of washes, and there was a significant difference in the physical durability of polyethylene and polyester based LLINs (p=O.026). The study recommends that LLINs should not be washed using a local method of beating nets on rocks. Further, LLINs should not be washed more than two times in a year and replacement of LLINs should be done within every 3 years. The results from this study are important in informing policy on the uses of LLINs in Kenya and other parts of the world.