PermaNet® 3.0 - 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 exhaustion¹. 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 resistance¹ 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.

** WHO susceptibility test with deltamethrin

Susceptible malaria vectors

Blood-feeding data:

• In both sites, the percentage of blood-fed mosquitoes caught in huts with unwashed PermaNet® 3.0 was significantly lower than with all other nets tested.
• Blood-feeding inhibition rates were highest in huts with unwashed PermaNet® 3.0 in both sites, ranging from 90.74% in Tanzania to 81.2% in Vietnam.

PermaNet® 3.0 fulfilled WHOPES Phase 2 criteria for a LN in a susceptible site and in the resistant test site in Vietnam.

Mortality data:

• In both sites, washed and unwashed PermaNet® 3.0 performed significantly better than a conventionally treated net washed until just before exhaustion.
  
• In both sites, the mortality rate in huts with PermaNet® 3.0 washed 20 times was significantly higher than with PermaNet® 2.0 washed 20 times.

PermaNet 3.0 fulfilled WHOPES Phase 2 criteria for a LN in a susceptible site and in the resistant test site in Vietnam.

Graphs to show overall blood-feeding (%) and mortality (%) of wild, freeflying, susceptible Anopheles populations caught at two test sites. Error bars show 95% confidence limits. Letters indicate results from statistical comparisons; data from one test site sharing the same letter do not differ significantly (P>0.05). *Vietnam is a site with pyrethroid resistance that does not yet have any impact on the performance of the nets tested.

Resistant malaria vectors

Blood-feeding data

• In Burkina Faso, an area with a high frequency of kdr mutation, the % blood-fed mosquitoes caught in huts with PermaNet® 3.0 was significantly lower than with washed and unwashed PermaNet® 2.0.
• In Burkina Faso, blood-feeding inhibition rates were highest with unwashed PermaNet® 3.0 (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 % bloodfed mosquitoes were caught in huts 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

PermaNet® 3.0 performed equal to or better than PermaNet® 2.0 in the resistant test sites.

Mortality data

• The mortality rate in Burkina Faso, an area with a high frequency of kdr mutation, was significantly higher in huts with washed and unwashed PermaNet® 3.0 than with washed and unwashed PermaNet® 2.0.
• The mortality rate in Cameroon, an area with metabolic resistance, was significantly higher in huts with washed and unwashed PermaNet® 3.0 than with washed and unwashed PermaNet® 2.0.
• In both sites, PermaNet® 3.0 washed 20times performed as well as unwashed PermaNet® 2.0

PermaNet® 3.0 performed significantly better than PermaNet® 2.0 in resistant test sites.

Graphs to show overall blood-feeding (%) and mortality (%) of wild, freeflying, pyrethroid-resistant Anopheles populations caught at two test sites. Error bars show 95% confidence limits. Letters indicate results from statistical comparisons; data from one test site sharing the same letter do not differ significantly (P>0.05).

References

1. 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.