Field Durability of <i>Yorkool<sup>®</sup>LN</i> Nets in the Benin Republic

CONTEXT: Recent publications on WHO recommended methods for estimating the survival of LLINs are good guidelines for assessing the performance of long-lasting insecticidal nets (LLINs). Thus, this field trial study was undertaken to evaluate the durability of the Yorkool® LN mosquito net distributed during the 2017 campaign in Benin. METHODS: The monitoring of Yorkool® LN nets was carried out in two districts (Djougou III and Barienou) in Djougou, department of Donga, northern Benin from October 2017 to March 2019. A representative sample of 250 households that had received the Yorkool® LN polyester LLINs during the 2017 campaign was selected in the rural and urban areas of each district and monitored for 6, 12 and 18 months. An evaluation of the survival of Yorkool® LN nets was conducted based on the rate of loss and physical condition of the surviving nets as measured by the proportional hole index (pHI). Finally, the chemical efficacy of these LLINs during each period was determined using the WHO cone tests. RESULTS: Survival of Yorkool® LN nets was similar in both rural and urban areas, although there was a difference in survival between the 6-month (95.3%), 12-month (89.7%), and 18-month follow-up periods (74.4%). A difference in survival was also observed between the NetCalc model (84%) compared to the Yorkool® LN nets of this study (74.4%). The attrition rate was 29.6% for LLINs at 18 months. Surprisingly, the physical integrity of the LLINs was minimally affected in the municipality. Indeed, the proportion of mosquito nets in good condition without a hole was 51.8% compared to 56.8% with a hole after 18 months. Only 7.8% of the LLINs in the two districts were damaged compared to 2.6% which needed to be replaced. The washing frequency, location of the LLINs and the frequency of use are some factors contributing to the appearance of the holes in LLINs. The bio-efficacy results of LLINs based on the cone test were good with mortality rates of 74%, 66%, 72% and 58% respectively after baseline, 6, 12 and 18 months of use. CONCLUSIONS: The observed differences in the survival of Yorkool® LN nets are due to community living conditions and movements and not to the equipment used to manufacture LLINs. However, the estimated median survival has shown that Yorkool® LN nets would have an average lifespan of 2 years 8 months despite their fairly good physical condition. These results may be useful to the National Malaria Control Program (NMCP) during the period of replacement of these nets on the field

Malaria vectors resistance to insecticides in Benin: current trends and mechanisms involved

Abstract Background Insecticides are widely used to control malaria vectors and have significantly contributed to the reduction of malaria-caused mortality. In addition, the same classes of insecticides were widely introduced and used in agriculture in Benin since 1980s. These factors probably contributed to the selection of insecticide resistance in malaria vector populations reported in several localities in Benin. This insecticide resistance represents a threat to vector control tool and should be monitored. The present study reveals observed insecticide resistance trends in Benin to help for a better management of insecticide resistance. Methods Mosquito larvae were collected in eight sites and reared in laboratory. Bioassays were conducted on the adult mosquitoes upon the four types of insecticide currently used in public health in Benin. Knock-down resistance, insensitive acetylcholinesterase-1 resistance, and metabolic resistance analysis were performed in the mosquito populations based on molecular and biochemical analysis. The data were mapped using Geographical Information Systems (GIS) with Arcgis software. Results Mortalities observed with Deltamethrin (pyrethroid class) were less than 90% in 5 locations, between 90-97% in 2 locations, and over 98% in one location. Bendiocarb (carbamate class) showed mortalities ranged 90-97% in 2 locations and were over 98% in the others locations. A complete susceptibility to Pirimiphos methyl and Fenitrothion (organophosphate class) was observed in all locations with 98-100% mortalities. Knock-down resistance frequencies were high (0.78-0.96) and similar between Anopheles coluzzii, Anopheles gambiae, Anopheles arabiensis, and Anopheles melas. Insensitive acetylcholinesterase-1 was rare (0.002-0.1) and only detected in Anopheles gambiae in concomitance with Knock-down resistance mutation. The maps showed a large distribution of Deltamethrin resistance, Knock-down mutation and metabolic resistance throughout the country, a suspected resistance to Bendiocarb and detection of insensitive acetylcholinesterase-1 from northern Benin, and a wide distribution of susceptible vectors to Pirimiphos methyl and Fenitrothion. Conclusion This study showed a widespread resistance of malaria vectors to pyrethroid previously located in southern Benin, an early emergence of carbamates resistance from northern Benin and a full susceptibility to organophosphates. Several resistance mechanisms were detected in vectors with a potential cross resistance to pyrethroids through Knock-down and metabolic resistance mechanisms