National Malaria Control Forum

20112011

Vector Control/Ecology

NIMR/IHI/PMI/RTI/NMCP/WHO

Malaria vector control frontline

• Mosquito nets and Indoor residual spraying

have substantially reduced malaria

transmission.

Increase in bed net

coverage resulted in

reduction of the number

Russell et al Malaria Journal 9: 187

reduction of the number

of infective mosquito

bites a person receives

per year (EIR)

Insecticide resistance

• The use of pyrethroid insecticides in malaria vector control has increased dramatically in the past decade through the scale-up of ITN/LLINs & IRS campaigns

• LLINs products in current use contain only one class of insecticides: pyrethroids

• Inevitably the major malaria vectors have developed resistance to these insecticides and the resistance alleles are spreading at an exceptionally rapid rate throughout Africa.

Time series showing the sites that have reported insecticide resistance in

Africa.

Source: Coleman et al (2006). J. Med. Entomol. 43(4): 663-668

Distribution of pyrethroid resistance 2009(Source: Ranson et al., 2011)

Insecticide Resistance monitoring: Tanzania

Sites Surveyed in 2004/5 Sites Surveyed in 2008/9

2008/9 SURVEY: Key findings

• In Mainland Tanzania Anopheles mosquitoes continued to be highly susceptible to all insecticides tested (Deltamethrin, Permethrin, Lambdacyhalothrin & DDT).

• Reduced susceptibility recorded in some focal points e.g. DDT-DSM & Kyela, Lambda-Moshipoints e.g. DDT-DSM & Kyela, Lambda-Moshi

• There was no indication of development of resistance in populations of Anopheles where IRS have been extensively used e.g. Muleba

• Need for continuous close monitoring of insecticide resistance

R & D on New LLINs to Meet Universal

Coverage

The following pyrethroids have been tested in Tanzanian and were given Phase II interim approval by the WHO Pesticide Evaluation Scheme (WHOPES).

• Long Lasting Insecticide Nets (LLINs)• Long Lasting Insecticide Nets (LLINs)

Permanet® 3.0, Permanet® 2.0, Dawaplus 2.0, Lamdacyhalothrin, InterceptorTM, DuranetTM, Netprotect®.

• Long lasting treatment kits (LLTK)

Icon®Max.

Alternatives to Pyrethroids

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An. gambiae

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DN: Deltamethrin 5% SC

C-M: Chlorpyrifos methyl 24% CS

Malima et al. 2009 Med Vet Entomol 23: 317-325

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Treatment (mg/m2)

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Treatment (mg/m2)

Chlorpyrifos methyl has shown promising results with

efficacy comparable to Deltamethrin in terms of killing

mosquitoes.

Towards malaria elimination

What are the challenges in vector

control?

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Proportion of An. arabiensis increasing in Dar

es Salaam

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2005 2007 2008 2009

An merus

An arabiensis

An gambiae

Courtesy N. Govella, IHI

Indoors (πi). Outdoors.

The proportion of bites occurring outdoor has

increased.

Recent estimates from Dar es Salaam

(Govella et al, 2010) Pooled data from Zanzibar

(ZMCP / IHI / BMGF 2010)

Courtesy G. Devine, IHI

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Govella et al 2010 AJTMH 82: 415

Reduction in mosquito population size results in

increased fitness of remaining smaller

population• Individual fitness of malaria vectors is influenced

by density dependent (rainfall & temperature)

and density independent factors (e.g. body size)

• The remaining small population has fitness • The remaining small population has fitness

advantages; higher per capita growth, less

competition and more resources, and more

infectious

• Therefore targeting the remaining population,

may require more effort

Courtesy D. Wilson, IHI