Field evaluation of permethrin long-lasting insecticide treated nets (Olyset(®))
for malaria control in an endemic area, southeast of Iran.
Author(s): Soleimani-Ahmadi M, Vatandoost H, Shaeghi M, Raeisi A, Abedi F, Eshraghian MR,
Madani A, Safari R, Oshaghi MA, Abtahi M, Hajjaran H.
Affiliation(s): Department of Medical Entomology and Vector Control, School of Public Health &
National Institute of Health Research, Tehran University of Medical Sciences,
Tehran, Iran. mussasol@yahoo.com
Publication date & source: 2012, Acta Trop. , 123(3):146-53
Long lasting insecticide treated nets (LLINs) have been advocated as an effective
tool for prevention and control of malaria. Olyset net was the first LLINs which
became commercially available and obtained WHO approval. According to the
national strategic plan on evaluation of Olyset net, a field trial was conducted
to determine the efficacy of these nets against malaria vectors in an endemic
area in the southeast of Iran. Fourteen villages with similar topographical and
epidemiological situations were selected and randomly assigned to two clusters of
the study: Olyset net and untreated net. Distribution of nets was carried out to
cover 100% of the population in Olyset net and untreated net cluster. Anopheline
mosquitoes were collected monthly using different WHO standard methods in both
areas to determine their abundance, feeding pattern and resting behaviour. Human
blood index was determined using ELISA test. Additionally, Olyset nets were
evaluated for their biological activity using WHO cone bioassay test by
susceptible colony of Anopheles stephensi (Beech strain) and then for insecticide
residues by employing high performance thin layer chromatography. Malaria
incidence was measured by passive and active case detection from all study
population. In total 2115 adult anopheline mosquitoes were collected and
identified using morphological characters. They comprised of seven species:
Anopheles dthali (Liston), A. culicifacies (Giles), A. stephensi (Liston), A.
superpictus (Grassi), A.fluviatilis (James), A. moghulensis (Christophers) and A.
turkhudi (Liston). A. dthali, A. culicifacies and A. stephensi were most
prevalent species in both areas. In the Olyset net study area, there was a
significant reduction of 41.1%, 54.4%, 59.39% and 64.1% in the indoor-resting
density of A. culicifacies, A. stephensi, A. dthali and A. superpictus,
respectively, with an overall reduction of 39.3% in total mosquitoes in
comparison with untreated net area. A significant reduction was also observed in
human blood index of vector species in the Olyset net villages. Bioefficacy test
results of Olyset nets showed that the median knockdown time was 1.48 and
3.25min, while the average mortality rate was 100% and 72.3%±7.07 in baseline and
after 1 year of intervention, respectively. The average permethrin content
reached to 68.31% (683.1mg/m(2)) of the initial insecticide dose of
937±21.69mg/m(2) (nearly 1000mg/m(2)) at the end of intervention. Malaria
incidence was reduced by 96.6% and 64.8% in the village with Olyset nets and in
the villages with untreated nets, respectively. During intervention period, there
was a reduction of 93.2% in malaria incidence in Olyset net area as compared to
the untreated area. This study indicated that Olyset nets have a major impact on
malaria vectors and disease burden; therefore it could be recommended as an
effective personal protection tool for malaria control in malarious areas.
|