Background: Long-lasting insecticidal nets (LLINs) are widely used in sub-Saharan Africa to control the transmission of malaria parasites by Anopheles mosquitoes. However, their operational lifespan depends on numerous factors that are often not considered. This paper investigates on some of these factors likely associated with the rapid breakdown of LLINs efficacy in urban and rural locations of the seaport city of Kribi, South Region of Cameroon.Methods: The cross-sectional study conducted in June 2019 included: (i) a household survey using standard questionnaire for brands of LLINs used, their maintenance, and coverage rates in study communities, (ii) assessment of the physical integrity of nets, and (iii) WHO cone bioassays to check the residual efficacy of the nets against wild strains and susceptible reference laboratory strains of Anopheles gambiae s. l. species.Results: A total of 540 households were surveyed, 235 in urban Kribi and 305 in rural Kribi. The overall net coverage rate per sleeping space was 68.82%, irrespectively with a similar trend between rural Kribi (68.98%) and urban Kribi (68.62%) (p = 0.929). Of the 1,211 LLINs counted, 64.73% were Interceptor®, 25.44% were PermaNet®, 4.68% were Olyset Net ; the remainder (05.13%) belonged to Yorkool®, Royal Sentry®, Netto®, Super Net® and Panda Net®. Proportional hole index analysis showed that Permanet 2.0 nets (1435±117.462) were more degraded than other brands after more than 36 months of use in rural Kribi, whereas Yorkool nets (2004±328.833) were more degraded in urban Kribi. Polyethylene fibers were not significantly more degraded than polyester fibers. The bio efficacy tests showed that LLINs washed more than 20 times induced mortality from 21.6% to 99.6% for the Kisumu strain and from 0.8% to 76.50% for the wild strain. LLINs washed with Marseille soap retained their lethal properties significantly more than LLINs washed with corrosive detergents (p=0.000). Similarly, LLINs spread in the shade retained their lethal properties more than those spread in the sun.Conclusion: Corrosive detergents and sunlight are factors that negate the toxic effect of insecticide impregnation of LLINs. Awareness campaigns are needed to encourage people to adopt good LLIN care practices.

Background: Long-lasting insecticidal nets (LLINs) are widely used in sub-Saharan Africa to control the transmission of malaria parasites by Anopheles mosquitoes. However, their operational lifespan depends on numerous factors that are often not considered. This paper investigates on some of the factors likely associated with the rapid breakdown of LLINs efficacy in urban and rural settings of the seaport city of Kribi, South Region of Cameroon. Methods: A cross-sectional survey was conducted in June 2019 including: (i) a household survey using standard questionnaire for brands of LLINs used, their maintenance, and coverage rates in study communities, (ii) assessment of the physical integrity of nets, and (iii) WHO cone bioassays to determine the residual efficacy of the nets against wild strains and susceptible reference laboratory strains of Anopheles gambiae s. l. species. Results: A total of 540 households were surveyed, 235 in Kribi- urban and 305 in Kribi-rural. The overall net coverage rate per sleeping space was 68.82%, irrespectively with a similar trend between Kribi-rural (68.98%) and Kribi-urban (68.62%) (p = 0.929). Of the 1,211 LLINs recorded, 64.73% were Interceptor®, 25.44% were PermaNet®, 4.68% were Olyset Net ; the remainder (05.13%) belonged to Yorkool®, Royal Sentry®, Netto®, Super Net® and Panda Net®. The hole indices were significantly correlated to the frequency of washes in kribi-urban as well as kribi-rural settings (p≤ 10-3). Nets washed with ordinary soap had lower hole indices compared to nets washed with corrosive detergents in the two groups of settings in the study area (p≤ 10-4). Likewise, nets dried under the sun significantly recorded a higher hole indices compared to nets dried in a shaded area (p≤ 0.04) in the two groups of settings. Polyethylene fibers were significantly less degraded than polyester fibers. The bio efficacy results revealed 21.6% - 99.6% mortality rates of the Kisumu strain exposed to LLINs washed more than 20 times and from 0.8% to 76.50% for the wild strain. LLINs washed with ordinary soap significantly retained their lethal properties more than LLINs washed with corrosive detergents (p=10-4). Similarly, LLINs dried in the shade retained their lethal properties more than those spread in the sun.Conclusion: Excessive washes, Corrosive detergents and drying regimes are factors that degrade the toxic effect of insecticide impregnated on LLINs. Awareness campaigns are needed to encourage people to adopt good LLIN maintainance practices.