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Vector Control for Disease Mitigation

Vector Control for Disease Mitigation IMERGARD WP: A Mechanical Insecticide with a New Mode of Action IRS and 11 months' Residual Efficacy

Imergard™ WP (wettable powder) is a perlite-based indoor and outdoor residual spray (IRS/ORS)  designed to provide a physical mode of action against mosquitoes capable of harboring or transmitting human disease.

In their 2019 annual report, the World Health Organization (WHO), reported 405,000 deaths from malaria, 67% of which were children under the age of five years old. Indoor residual sprays (IRS) have been an effective strategy to control malaria transmission, and have helped reduce the number of deaths in recent years. However, the overuse of traditional IRS pesticides has pushed natural selection towards resistance. Fewer people at risk of malaria are being protected by the IRS; declining from a peak of 5% coverage in 2010 to 2% in 2018 primarily as a result of insecticide resistance and rising costs of new technologies.

“If IRS is to remain an important element in an integrated vector control approach for sub-Saharan Africa, alternative insecticides, particularly ones with novel modes of action are urgently needed. Dr. Sarah J Moore, Ifakara Health Institute and Swiss Tropical and Public Health Institute, RBM Partnership To End Malaria, 2020

A new mode of action IRS with 11 months' residual efficacy

Imergard WP (Wettable Powder) is a mechanical insecticide providing a physical mode of action. It is applied to interior walls using standard backpack spray equipment. When the mosquito lands on a treated surface, there is a static transfer of Imergard WP particles, which absorb the lipid layer necessary for the mosquito’s survival.

Figure 1: Imergard WP IRS Awareness Training, Umme Tanzania, 18 September 2018

In a community trial completed in 2020 in Tanzania where over 4,000 houses were treated, Imergard WP was able to control the malaria parasite as effectively as the gold standard positive control, a micro-encapsulated Pirimiphos-methyl IRS. At the conclusion of the study, Imergard WP maintained 100% efficacy after 72 hours against a threshold target of 80% mortality on all substrates to 11 months.  Imergard WP held its own against the gold standard which is an impressive result for a mechanical insecticide, considering that the mosquitos in this study were susceptible to micro-encapsulated Pirimiphos-methyl.


Graph 1 shows the monthly residual efficacy on all substrates (brick, cement and mud) of Imergard WP and gold standard after spraying 1 to 12 months against laboratory reared, pyrethroid susceptible Anopheles gambiae s.s. Graphs 2 - 4 provide a breakdown by substrate. Both the Imergard WP and the positive control achieved the threshold 12 month residual efficacy on cement after 120hrs.

Graph 1.

Graph 1: All substrate residual efficacy of Imergard WP and gold standard by month after spraying 1 to 12 months against pyrethroid susceptible Anopheles gambiae s.s

Graph 2.

Graph 2: 72hr residual efficacy of Imergard WP and gold standard on brick substrate after spraying 1 to 12 months against pyrethroid susceptible Anopheles gambiae s.s

Graph 3.

Graph 3: 72hr residual efficacy of Imergard WP and gold standard on cement substrate after spraying 1 to 12 months against pyrethroid susceptible Anopheles gambiae s.s

Graph 4.

Graph 4: 72hr residual efficacy of Imergard WP and gold standard on mud substrate after spraying 1 to 12 months against pyrethroid susceptible Anopheles gambiae s.s. Note month 1 for Imergard WP also has the 96hr residual efficacy average data point.

Graph 5 shows the monthly residual efficacy on all substrates (brick, cement and mud) of Imergard WP and gold standard after spraying 6 to 12 months against laboratory reared, strongly pyrethroid resistant Anopheles arabiensis Kining’ina strain. Graphs 6 - 8 provide a breakdown by substrate.

Graph 5.

Graph 5: All substrate residual efficacy of Imergard WP and gold standard by month after spraying 6 to 12 months against pyrethroid resistant Anopheles arabiensis Kining’ina strain

Graph 6.

Graph 6: 72hr residual efficacy of Imergard WP and gold standard on brick substrate after spraying 6 to 12 months against pyrethroid resistant Anopheles arabiensis Kining’ina strain

Graph 7.

Graph 7: 72hr residual efficacy of Imergard WP and gold standard on cement substrate after spraying 6 to 12 months against pyrethroid resistant Anopheles arabiensis Kining’ina strain

Graph 8.

Graph 8: 72hr residual efficacy of Imergard WP and gold standard on mud substrate after spraying 6 to 12 months against pyrethroid resistant Anopheles arabiensis Kining’ina strain. Note month 11 for Imergard WP also has the 96hr residual efficacy average

An IRS that has 11 months of residual efficacy means it can be applied at any time of the year and not just during mosquito season, potentially driving an increase in IRS coverage.

High user acceptance and new potential treatment areas

There was a high level of user acceptance in the community trial involving 15 villages and 13540 men, women and children and no serious adverse events were reported among sprayers or residents.

Imergard WP, like other IRS technologies, does not stop mosquitoes from blood-feeding; this is where insecticide-treated bednets (ITN’s) have proven an invaluable tool with 50% of the population at risk being protected in 2018. However, in 2018 nearly 40% of pregnant women and children under five years of age, the most vulnerable population, did not sleep under an ITNs.

The primary objective of employing IRS as a strategy for malaria control is to limit the spread of the malaria parasite. After a blood meal, mosquitoes typically rest indoors prior to laying eggs. If mosquitoes don’t live longer than 10-14 days they will not live long enough to transmit the malaria parasite.

Imergard WP’s advantage is that it provides a physical mode of action and is a powerful tool in resistance management. 

It is not a silver bullet, but it will deter cross-chemical resistance development and complement traditional and new IRS chemistry. 

Since Imergard WP is not subject to UV or heat degradation, it potentially opens up a new large surface area for residual application, e.g. outdoor surfaces that are under cover and indoor metal roofs.

 

No physical, chemical, human health or environmental hazards

The active ingredient of Imergard WP is perlite which has been processed to release its undiscovered  insecticidal properties. Since the accidental discovery of expanded perlite in 1939, it has been used in a wide range of industrial applications, including cosmetics, agriculture & horticulture, air & liquid filtration, fireproofing, insulation, etc.

Imergard WP has demonstrated efficacy against multiple Anopheles, Aedes and Culex s.s. It has a Toxicity Class IV rating which is the lowest rating and is non-toxic to bees when applied topically as a liquid suspension or a powder.

 

Imergard WP - Features & benefits

  • 11 months residual efficacy
  • Produced from a renewable and sustainable resource
  • A physical mode of action offers a new resistance management tool to deter cross-chemical resistance development
  • Use of Imergard  WP in rotation, mosaic or formulated with other IRS may be beneficial for insecticide resistance management
  • 5-year shelf life so it can be distributed to application sites months or years in advance
  • Applied with standard IRS backpack sprayers. Visual application cues allow sprayers and home residents to see where it has been sprayed
  • No odor and residents can enter the house immediately after application
  • Does not heat degrade so can be applied to tin ceilings
  • Demonstrated efficacy against multiple Anopheles, Aedes and Culex s.s.
  • Lowest Toxicity Class IV rating and is non-toxic to bees
  • Pending WHO Prequalification, WHO PQ, with a commercial launch anticipated in late 2020 or early 2021
  • Pending USA Environmental Protection Agency approval as a biopesticide for targeted IRS applications, with a commercial launch anticipated in late 2020 or early 2021

Imergard WP (Spanish version)

Imergard WP (Swahili version)

Volcanic Glass Spray Shows Promise in Controlling Mosquitoes https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7290382/

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