SA pi­lots ster­ile in­sect tech­nique

Weekend Argus (Sunday Edition) - - METRO - GIVE­MORE MUNHENGA The Con­ver­sa­tion

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.

Anophe­les ara­bi­en­sis

THE is re­spon­si­ble for most malaria trans­mis­sion in the coun­try.

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