Field efficacy and persistence of Long Lasting Insecticide treated mosquito Nets (LLINs) in comparison with conventional Insecticide Treated mosquito Nets (ITN) against malaria vector in Thailand

บทคัดย่อ

In Thailand, the conventional Insecticide Treated mosquito Nets or ITN have been used over the years by the villagers. These mosquito nets are treated with permethrin 10%w/w EC manually as under the guidance of the health workers. These treated nets have efficacy for 6 months and need re-treated again. Long Lasting Insecticide treated mosquito Nets or LLINS, which can retain persistence for at least 3 years, are being considered to replace the conventional ITN. This study is intended to monitor the bioefficacy of two products of LLINS under field conditions in Thailand. These nets are PermaNet^® and OlysetNet^®

The study was carried out in a malaria endemic area of Kanchanaburi province. PermeNet^®, OlysetNet^® and conventional ITN were distributed to the households in Baan-Su-Phan hamlet of village no.5, Loom-Soom subdistrict of Sai-Yok district and the households were allowed to use the bed nets. The nets were washed at every 6 months intervals and only conventional ITN were re-treated after washings. WHO standard procedures for cone bioassay tests were conducted with the bed net samples collected from the households that were using the nets and laboratory reared Anopheles minimus. The mosquitoes were exposed to the mosquito net samples for 3 minutes and the mortality rates were measured after 24 hours recovery period. Bioassays were carried out every month continuously for 3 years. The community acceptance of LLINS was studied by informal interview of the net users.

Results of the study showed that both LLINS (PermaNet^® and OlysetNet^®) offered > 80% mortality on Anopheles minimus over the entire 3 years period of field evaluation. The conventional ITN performed similar to LLINs except the fact that ITN were re-treated at 6 months intervals. Interestingly the ITN offered only 15% mortality after 6 months use and were washed without re-treatment.

The qualitative data on community acceptance of LLINs revealed that the majority of the households prefer PermaNet^® due to its soft nature of net material, easy to wash and pack after use.