Impregnated mesh to be added to arsenal in fight against mosquitoes
Researchers at the University of Pretoria offer an alternative to residual spraying, writes Sarah Wild
Malaria kills a child every five minutes, according to the World Health Organisation.
This is particularly true in sub-Saharan Africa, which accounts for more than 90% of the world’s 400,000 annual malaria deaths.
SA is a success story in malaria eradication, with the state footing the bill and the credit. It spent an average of $25m annually between 2009 and 2012 on malaria-control and plans to wipe out the disease from its territory by 2018.
But climate change could see malaria and other mosquito-borne diseases creeping across SA’s borders as weather patterns shift and extend mosquitoes’ habitats and the disease’s infection vectors.
Research out of the University of Pretoria hopes to add another weapon to the world’s malaria-fighting arsenal: a mesh impregnated with insecticides that kills mosquitoes on contact.
The Department of Health’s malaria strategy involves spraying insecticides such as DDT inside the houses of people who live in high-risk areas.
Malaria is endemic in parts of Limpopo, Mpumalanga and KwaZulu-Natal, with about 4.9-million people at risk of contracting the parasite carried by certain mosquitoes.
However, insecticides have to be sprayed regularly and there are concerns about excessive exposure to the chemicals.
Researchers hope that the mesh will offer a longer-lasting and safer alternative to indoor residual spraying, the mainstay of SA’s malaria success.
The mesh looks like the sacks used to package onions, but it is rigid and comes in a range of colours: from plain white to purple or orange.
"The trial linings are installed on the upper part of the wall only where mosquitoes tend to rest after a blood meal," says Dr Taneshka Kruger, who manages the project at the University of Pretoria’s Institute for Sustainable Malaria Control. The mesh is about the length of a forearm and since it is near the ceiling, is out of reach of children.
The chemicals it is infused with — organic compounds known as pyrethroids — are not toxic to mammals (except cats). But "touching them is not recommended", Kruger says, as they could cause skin irritation.
Product development is fairly advanced — the university’s Institute of Applied Materials originally developed the mesh in 2011 and researchers have been testing it since.
A 2012 six-month trial in the Vhembe district in Limpopo, conducted by the Institute for Sustainable Malaria Control, found that it killed all the mosquitoes that landed on it. Malaria is endemic in this part of the country and mosquitoes
are usually controlled with indoor spraying.
But the major question researchers were looking to answer in the trial was whether people would have the meshes in their homes. Many technological interventions fail because the communities they are intended to help reject them.
But participants embraced the impregnated mesh and decided to keep them after the trial ended — they said that it was decorative and killed mosquitoes as well as other insects.
The academics have finished a four-year efficacy study, with the financial support of commercial partners Avima, a pesticide company, and Huhtamaki SA, a packaging manufacturer. The project recently received a grant from the Technology Innovation Agency — a government agency tasked with bridging the gap between innovative idea and marketable product — to boost its technological readiness. The Department of Health recommends that home owners use this sort of intervention.
The results of the 2012 trial were "a good indication that the community members were aware of malaria-prevention measures and would be willing to protect themselves if they could afford the lining
The results of the 2012 trial were "a good indication that the community members were aware of malaria-prevention measures and would be willing to protect themselves if they could afford the lining", says Popo Maja, communications manager at the department.
But reports that it kills mosquitoes are not enough — they need data.
"The bottom line for measuring impact or success of any vector-control intervention should be the reduction in incidence of local malaria cases," he says. In the 2015-16 season, local cases of malaria increased in the Vhembe district of Limpopo, so the researchers would need to show that malaria cases went down among participants in their study.
"It would be necessary to show evidence of reduction of malaria vector mosquitoes before and after the intervention, as opposed to only focusing on mosquito bites which may occur from nuisance mosquitoes," Maja says.
To consider this intervention as part of its malaria eradication plans, the department would need to see evidence linking the mesh to a reduction in malaria, rather than some of its other interventions, such as larvicide in terms of which officials ensure that mosquito larvae do not breed in water sources.
Kruger says that once all the field trials have been completed and they have shown the mesh is effective, they will look at rolling it out commercially.