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MALARIA: New study finds participatory approaches useful for "mosquito proofing" houses

Nov. 24, 2022
MALARIA: New study finds participatory approaches useful for "mosquito proofing" houses
A snip from the MALARIA journal with insets of Ifakara Health Institute researchers, Rogath Msoffe and Marcelina Finda, who contributed to the study and publication. GRAPHIC |IFAKARA/Coms.

Participatory approaches to mosquito proofing for houses may be acceptable and effective in rural settings of the malaria endemic countries in the Sub-Saharan Africa region; latest study findings have revealed.

The study was conducted for ten months involving communities residing in the four Kilombero Valley neighborhoods of Katindiuka, Viwanja Sitini, Mlabani, and Lipangala which administratively fall within Ifakara Town.

Ifakara researchers Rogath Msoffe, Matilda Hewitt, John Masalu, Marcelina Finda, Deogratius Kavishe, Fredros Okumu, Emmanuel Mpolya, Emmanuel Kaindoa & Gerry Killeen contributed to the study, whose findings were published on the Malaria Journal on November 5, 2022.

The researchers report they engaged members of a rural Tanzanian community in developing and evaluating simple, affordable and scalable procedures for installing readily available screening materials on eave gaps and windows of their own houses, and then treating those screens with a widely used spray formulation technically known as “organophosphate insecticide pirimiphos-methyl” or simply “PM.”

“Almost all (52) recruited households participated until the end, at which point all houses had been successfully screened. In most cases, screening was only installed after making enabling structural modifications that were accepted by the enrolled households,” they report.

Results showed that compared to those unscreened, houses with either treated or untreated screens both almost entirely excluded a mosquito species spreading malaria – technically named Anopheles arabiensis – the most abundant local malaria vector by 98%. However, the results revealed that screening was far less effective against a non-malaria vector – technically named Culex quinquefasciatus – best known for causing considerable biting nuisance, but not spreading malaria.

Researchers believe insecticidal mosquito-proof netting screens could combine the best features of insecticide-treated nets (ITNs) and indoor residual spraying (IRS), the two most important front line vector control interventions in Africa today, and also overcome the most important limitations of these methods.

“Indoor mosquito densities were surveyed longitudinally, for approximately 3 months before and over 5 months after participatory house modification and screening using locally available materials… In most cases, screening was only installed after making enabling structural modifications that were accepted by the enrolled households,” the researchers report.

Based on the results, the researchers conclude: “Participatory approaches to mosquito proofing houses may be acceptable and effective,” and express optimism that installed screens may be suitable targets for residual insecticide treatments.

More: About malaria vector mosquitos
Across most of sub-Saharan Africa, including Tanzania, the most important malaria vector mosquito species are Anopheles gambiae sensu stricto (s.s.), Anopheles coluzzii, Anopheles funestus, and Anopheles arabiensis. The first three species are the most efficient and important vectors but also the most vulnerable to control with long-lasting insecticidal nets (LLIN) and indoor residual spray (IRS) insecticides because they are highly specialized for feeding on humans while they are indoors at night and usually rest indoors too.

Even untreated mosquito-proof screening for houses can suppress densities of indoor-feeding mosquitoes, and it is notable that impact appears to vary in proportion to the preference of the mosquito species for human blood.

The potential for insecticide-treated house screening may be even greater, even for vector species like An. arabiensis that are considered behaviourally evasive because they can feed on people or animals outdoors and only visit houses very briefly in search of blood.

About malaria transmission in Africa
Historically, the vast majority of malaria transmission in Africa has occurred indoors because mosquitoes were able to freely enter most houses and attack unprotected people. Structural features which have been proven to be risk factors for malaria infection include the absence of a celling, open eaves, windows and gaps in the walls, especially around door and window frames, and gaps in the doors themselves.

A systematic review and meta-analysis of studies from across Africa indicate that people living in improved housing had, on average, 47% lower odds of chronically carrying malaria and a 45 to 65% lower odds of experiencing acute symptomatic clinical malaria. Another review article indicates that African children living in modern houses are up to 14% less likely to have malaria compared to the children living in traditional houses.

House screening benefits
While the epidemiological benefits of house screening have been well documented, a lack of evidence demonstrating the affordability, acceptability, and practicability of mosquito proofing for typical African houses is still considered an obstacle to scale up.

Enabling households to afford and apply a particular house screening intervention in a given context requires careful consideration of what materials are readily available, what community engagement practices may be acceptable to householders and local authorities, and what installation procedures may suit the most basic local house designs occupied by low-income households. Moreover, it is essential that community members and leaders are involved from the outset in development and implementation of approaches for mosquito screening their houses.

Screened houses will have to do more than just exclude mosquitoes: they will also have to kill them when they attempt to enter or exit the house. Treated netting screens for mosquito proofing houses have several advantages over treated nets and indoor sprays as an insecticide deployment format because it combines essential features of these interventions while also overcoming some of their limitations.

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>> Read the journal article: Participatory development of practical, affordable, insecticide-treated mosquito proofing for a range of housing designs in rural southern Tanzania

>> For inquiries about the study – email the corresponding author: rmsoffe@ihi.or.tz