New methodological approaches to monitor long lasting insecticidal nets (LLINs) durability for sustained malaria control

Long lasting insecticidal nets (LLINs) are the current primary vector control measure to prevent malaria transmission. They function by inhibiting mosquitoes from blood feeding and also killing mosquitoes and hence provide personal and community protection respectively. With findings from different LLIN distribution programmes in different settings, it is assumed that the effective life of LLINs is 3 years. This is mostly due to wear and tear of the fabric and hence need for the introduction of the guidelines that provide standard methods to monitor the longevity of LLINs. The standard means established to monitor longevity of ITN is through cone bioassays, WHO tunnel tests and experimental hut evaluations. However, all the standard methods for assessing LLIN durability have limitations and the information collected on LLIN durability will only be useful if correctly collected using simple, realistic and reproducible methods. Thus to address this issue of high public health significance, we undertook two projects namely 1) ABCDR (Attrition, Bioefficacy, Chemical residual, Damage and Resistance) and 2) Holed Net project. The ABCDR project aimed at understanding of bednet durability in malaria endemic countries and factors affecting bednet durability with the main focus of using that information in improving the current methodologies by developing simple, realistic methods for assessing bednet efficacy while Holed Net project, aimed at understanding the association of size and location of net damage and interaction with insecticide concentration in order to ensure their continued efficacy and also work with manufacturers to optimize their longevity. The results showed that, Of 6067 campaign nets reported to have been received between 2009 and 2011, 35 % (2145 nets) were no longer present. In addition, most of those nets had been discarded (84 %) mainly because they were too torn (94 %) and only 39 % of distributed nets remain both present and in serviceable physical condition, a functional survival considerably below WHO assumptions of 50 % survival of a ‘three- year’ net. However, the majority of nets still retained substantial levels of permethrin and could still be bio-chemically useful against mosquitoes if their holes were repaired, adding evidence to the value of net care and repair campaigns. In conclusion, the findings from this study provided not only a deep insight into many aspects of LLIN durability but also evidence for revising the existing standard methods for LLIN durability. It also served as baseline information that was used to revise; i) the measurement of the standard entomological parameters i.e. mortality and blood feeding inhibition in order to develop a logistically simple, time saving and realistic method for assessing LLIN durability and ii) the measurement of proportional hole index (phi) in order to develop a “location adjusted phi”. Through findings from these studies, new bioassays have been developed to measure bednet durability with high throughput and robust data power. The developed bioassays are simple to use, very cost effective and reproducible for use in multiple countries.