Fungus can be used to reduce malaria transmission, two research groups have announced. Malaria is transmitted between people by blood-feeding mosquitoes. By infecting mosquitoes with fungi while they are digesting human blood, malaria transmission can be drastically reduced.
Insecticides like DDT have been used for decades to kill the mosquitoes which transmit malaria. However, many mosquitoes have become resistant to chemical pesticides. The new approach, announced in the journal Science (June 10 issue), is to use a fungus as a biological pesticide. Inert fungal spores are impregnated on cloth or netting, or sprayed on house walls or ceilings. When a mosquito touches the spores, the fungus germinates, penetrating the mosquito and growing within it. The mosquito succumbs to the fungus before it has begun to transmit malaria.
Scientists at Edinburgh University and Imperial College discovered that fungal infection reduced malaria transmission in the laboratory by 98%. Mostly the mosquitoes died before they became infectious. But the fungus also reduced transmission by interrupting mosquito feeding and may also have directly interfered with the malaria parasites in the mosquito. “It seems likely that fungal-infected mosquitoes will also fly less well, and produce fewer eggs” said Dr Simon Blanford of Edinburgh University, who did the laboratory work.
The method is practical for Africa according to scientists from a research consortium involving the Ifakara Health Research and Development Centre in Tanzania, the Swiss Tropical Institute in Basel, Switzerland and Wageningen University, in The Netherlands. They hung fungus-impregnated black sheets inside African houses near Ifakara, in central Tanzania. Mosquitoes resting on these sheets after taking a blood meal became infected and died. In houses in this area, people are bitten almost once a night by a malaria-carrying mosquito. Mathematical calculations showed that the use of fungal-impregnated sheets could reduce this to once every three weeks.
“The results are extremely encouraging” said Ernst-Jan Scholte, who led the field-work. “The fungi provide another tool for use in the fight against malaria”. His Tanzanian counterpart, Kija Ng’habi, emphasized the desire to push this research line further “This technology needs to be developed to be manageable and affordable. We need to evaluate this on a larger scale in communities that have little resources”. This is the first biological control agent for adult malaria mosquitoes and could contribute to real health benefits if incorporated into integrated malaria programmes, said Dr Gerry Killeen of the Ifakara Health Research and Development Centre and the Swiss Tropical Institute “If this fungus can kill mosquitoes and prevent malaria it merits serious investigation. We need alternatives to chemical insecticides, especially DDT”. The trial results were warmly received by the community in which it took place: “Everybody in the village would like to have this dawa (medicine) tomorrow so there’s clearly a demand from the end user that we can’t yet fulfill”.
“There is no evidence that insects can develop resistance to fungi” said Dr Matt Thomas of Imperial College, one of the leaders of the work. However, even mosquitoes were to become resistant, it is extremely unlikely that they would also be resistant to chemical pesticides. “It should be possible to use the chemical and biological pesticides together or in rotation to prolong their usefulness”, said Professor Andrew Read of Edinburgh University, one of the group leaders.
Contacts
Edinburgh: Professor Andrew Read, +44 131 650 5506, +44 (0)7909913861 (mob) a.read@ed.ac.uk
Imperial: Dr Matt Thomas +44 (0)207 594 2657 +44 (0) 7952910734 (mob) m.thomas@imperial.ac.uk
Tanzania: Kija Ng’habi +255-748-706110 (mob), kija@ifakara.mimcom.net, and Dr Gerry Killeen +255-748-477118 (mob) gkilleen@ifakara.mimcom.net
Wageningen: Dr Willem Takken, +31(0)317 484075 Willem.Takken@wur.nl, and Dr Bart Knols +43 (0) 1 2600 28426, +43 (0)664 923 2875 (mob) b.knols@iaea.org
Pictures
Available for free download at the http://readgroup.icapb.ed.ac.uk/hugh_photos.html. Photo credit: Hugh Sturrock.