SA pilots sterile insect technique
SOUTH Africa is one of four southern African countries aiming to eliminate malaria transmission by 2023. Indoor spraying using DDT and pyrethroid insecticides constitutes the backbone of its malaria control programmes.
Effective vector control by indoor residual spraying has been key in the reduction of cases. This was instrumental in creating malaria-free zones in most parts of the country. Malaria transmission is now limited to the north-eastern parts of Limpopo province, the lowveld areas of Mpumalanga and the far northern parts of KwaZuluNatal.
Failure to eliminate malaria transmission is attributed, in part, to resistance to the insecticides being used. Added to this is the challenge of controlling the outdoor-biting Anopheles arabiensis population that’s largely considered responsible for most malaria transmission in the country.
Indoor spraying isn’t completely effective against this mosquito because it mainly targets indoor biting and resting mosquitoes. This strategy is not adequate against vectors that sometimes feed and rest outdoors, such as Anopheles arabiensis.
Other complementary vector control strategies are needed to eliminate the disease. These must be able to control outdoor feeding and resting mosquito populations.
One possible approach is a technique that involves sterilising the insects. The technology is being assessed in South Africa. It involves a genetic birth control method in which laboratory mass-produced sterile male insects are released into the wild at a ratio that inundates a target population. This forces females to mate with sterile males, reducing fecundity, and resulting in population suppression.
The sterile insect technique has been piloted against mosquito vectors of Zika, yellow fever, chikungunya and dengue viruses, but has never been used for malaria control. The sterile insect technique initiative and a similar trial in Sudan are a first for African malaria vectors.
Preparations for the South African project are at an advanced stage. A pilot mass-rearing facility has been built and the size of the natural mosquito population has been estimated. In addition, a local community has been drawn into preparations and is now ready for a trial run.
All these steps pave the way for a pilot demonstration.
The sterile insect technique has been applied successfully against other insect pests including the fruit fly and the new-world screwworm fly. In South Africa, this technology is routinely used in Citrusdal, Western Cape, to control the false codling moth.
The project involving Anopheles arabiensis aims to show that the sterile insect technique can be used successfully to suppress mosquito populations that carry and spread malaria. If it works, the approach can be used as an alternative vector control method to complement existing strategies. | Munhenga is a senior medical scientist at the National Institute for Communicable Diseases.
THE is responsible for most malaria transmission in the country.