|
 |
Efficacy Results
Small-scale field trials with PermaNet® 3.0 were performed in different ecological conditions using experimental huts. An experimental hut is a standardized village hut that has been constructed to facilitate the collection of mosquitoes and is routinely used for evaluating the efficacy of insecticide treated nets and other vector control products. The WHO Pesticide Evaluation Scheme (WHOPES) uses experimental huts with susceptible free flying, wild mosquitoes to investigate the efficacy of washed and unwashed LNs on mosquito behaviour.
The primary criteria used by WHOPES in evaluating LNs in experimental huts is blood feeding inhibition (the reduction in blood feeding compared with that in the control huts) and the mortality (the proportion of mosquitoes that are killed). A LN washed 20 times or more should perform equal to or better than a conventionally treated net washed until just before exhaustion16. PermaNet® 3.0 was evaluated in two sites, Tanzania and northern Benin, with susceptible Anopheles vector populations to establish its efficacy as a LN. The site in northern Benin has since been shown to have suspected resistance17 but since the extent and resistance mechanisms involved are not known, this data has been excluded.
PermaNet® 3.0 has been designed to give increased efficacy against pyrethroid resistant malaria vectors. There are currently no guidelines for evaluating products that have an effect on insecticide resistant vectors, including no established criteria with which to measure the efficacy of such a product. A pragmatic approach is therefore to compare the efficacy of a combination product (such as PermaNet® 3.0) with a mono-treated product (such as PermaNet® 2.0) in areas of known resistance. PermaNet® 3.0 was therefore tested in three sites with pyrethroid resistant Anopheles vector populations: Burkina Faso, Cameroon and Vietnam. Results from Vietnam showed that the level of resistance in the population is not yet having an impact on the performance of PermaNet® 2.0, therefore the data is presented with the susceptible site for comparison.
| Test site |
Species |
Insecticide susceptibility status** |
| Susceptible malaria vectors |
| Muheza, North-East Tanzania |
Anopheles gambiae s.s. |
Fully susceptible (WHO test 2008: 100% mortality) |
| Resistant malaria vectors (with no impact on net performance) |
| Bac Lieu, Southern Vietnam |
Anopheles epiroticus |
Pyrethroid resistant (WHO test 2008: 75% mortality) |
| Resistant malaria vectors |
| Kou Valley, Burkina Faso |
Anopheles gambiae s.s. |
Pyrethroid resistant (date of last WHO test unknown)
- High frequency of kdr mutation |
| Pitoa, Northern Cameroon |
Anopheles gambiae s.s. |
Pyrethroid resistant (date of last WHO test unknown)
-
Oxidase and esterase based metabolic resistance |
** WHO susceptibility test with deltamethrin |
 |
Figure 1. Graph to show % overall blood fed with a wild, free flying, susceptible Anopheles population caught in one test site.
*Vietnam is a site with pyrethroid resistance that does not yet have any impact on the control measures tested. Error bars show 95% confidence limits.
PermaNet® 3.0 fulfills WHOPES Phase 2 criteria for a LN in a susceptible site and in the resistant test site in Vietnam. |
Resistant malaria vectors
- In Burkina Faso, an area with a high frequency of kdr mutation, the % blood fed mosquitoes caught with PermaNet® 3.0, was significantly lower than with washed and unwashed PermaNet® 2.0.
- Blood feeding inhibition rates were highest with unwashed PermaNet® 3.0 in Burkina Faso (72.6%) and similar for unwashed PermaNet® 2.0 and PermaNet® 3.0 washed 20 times (53.4% and 52.0%, respectively).
- In Cameroon, an area with metabolic resistance, similar proportions of % blood fed mosquitoes were caught with PermaNet® 3.0 and PermaNet® 2.0.
- In Cameroon, blood feeding inhibition rates for PermaNet® 2.0 and 3.0 were higher than for the conventionally treated net washed to just before exhaustion.
|
 |
Figure 2. Graph to show % overall blood fed with wild, free flying, pyrethroid resistant Anopheles populations caught in two test sites. Error bars show 95% confidence limits.
PermaNet® 3.0 performed equal to or better than PermaNet® 2.0 in resistant test sites. |
Efficacy Results: Mortality data
Susceptible malaria vectors
- In both sites, both washed and unwashed PermaNet® 3.0 performed significantly better than a conventionally treated net washed until just before exhaustion.
- The mortality rate in Tanzania with PermaNet® 3.0 washed 20 times was significantly higher than with PermaNet® 2.0 washed 20 times.
- The mortality rate in Vietnam with washed and unwashed PermaNet® 3.0 was significantly higher than with washed and unwashed PermaNet® 2.0.
|
 |
Figure 3. Graph to show % overall mortality with a wild, free flying, susceptible Anopheles population caught in one test site. *Vietnam is a site with pyrethroid resistance that does not yet have any impact on the control measures tested. Error bars show 95% confidence limits.
PermaNet® 3.0 fulfills WHOPES Phase 2 criteria for a LN and performed equal to or better than PermaNet® 2.0 in the susceptible site and the resistant test site in Vietnam.
Resistant malaria vectors
- The mortality rate in Burkina Faso, an area with a high frequency of kdr mutation, with washed and unwashed PermaNet® 3.0 was significantly higher than with washed and unwashed PermaNet® 2.0.
- The mortality rate in Cameroon, an area with metabolic resistance, with washed and unwashed PermaNet® 3.0 was significantly higher than with washed and unwashed PermaNet® 2.0.
- In both sites, PermaNet® 3.0 washed 20 times performed as well as unwashed PermaNet® 2.0
|
 |
Figure 4. Graph to show % overall mortality with wild, free flying, pyrethroid resistant Anopheles populations caught in two test sites. Error bars show 95% confidence limits.
PermaNet® 3.0 performed significantly better than PermaNet® 2.0 in resistant test sites.
Quality Control
Vestergaard Frandsen maintains quality control standards necessary to meet WHOPES specifications. We are the only LN manufacturer with our own internal bioassay laboratory complying with WHO protocol. This ensures real time monitoring of quality. The bioassay lab, which is located in Vietnam, raises its own mosquitoes and performs cone and tunnel tests in order to test the mortality, knock-down and blood feeding inhibition of PermaNet®.
The chemical laboratories in Vietnam and Thailand measure the chemical dosage on the net, while the textile laboratories in Vietnam and Thailand focus on the intricate details such as width, mesh and weight control, bursting strength of the netting material and dimensional stability in washing and drying. |
|
| |
|
|
- WHO (2005) Guidelines for laboratory and field testing of long-lasting insecticidal mosquito nets. WHO/CDS/WHOPES/GCDPP/2005.11. World Health Organization, Geneva, Switzerland: 18pp.
- WHO (2009) Report of the twelfth WHOPES Working Group meeting. World Health Organization, Geneva, Switzerland: 120pp.
|
|
|
About Us