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Study finds fungus is effective agent in fight against malaria

News release distributed by University of Edinburgh

19.00 (BST) THURSDAY 9 JUNE 2005

High-resolution pics available free at

Scientists have discovered an unlikely ally in the fight against malaria. Infecting mosquitoes with fungi can drastically reduce transmission of the disease, surprising new research from the University of Edinburgh and Imperial College London, reveals. A study in Science journal suggests that infecting mosquitoes with fungi while they digest human blood could help to significantly curb the disease that claims at lease a million lives each year.

Top: freshly fed Anopheles, Middle: mosquito killed by fungus 12 hours earlier, Bottom: mosquito killed by fungus 24 hours

Insecticides like DDT have been used for decades to kill the mosquitoes that transmit malaria, but many mosquitoes have become resistant to chemical pesticides. By contrast, this radical new approach uses 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.

The Edinburgh and Imperial scientists discovered that fungal infection reduced malaria transmission in the laboratory by 98 per cent. 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 the University of Edinburgh's School of Biological Sciences, who carried out the laboratory work.

"There is no evidence that insects can develop resistance to fungi," said Dr Matt Thomas of Imperial College London, one of the leaders of the work. However, even if 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 Dr Thomas.

The method would be practical in Africa, according to a companion paper in Science by scientists from a research consortium involving the Ifakara Health Research and Development Centre in Tanzania, the Swiss Tropical Institute in Basel and Wageningen University in The Netherlands. They hung fungus-impregnated black sheets inside African houses near Ifakara, in central Tanzania, and found that 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 fieldwork. "The fungi provide another tool for use in the fight against malaria." His Tanzanian counterpart, Kija Nghabi, emphasised 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 it 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, then 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 theres clearly a demand from the end user that we cant yet fulfill," said Dr Killeen.

For further information, please contact:

Professor Andrew Read, University of Edinburgh
Tel: +44 (0) 131 650 5506 or +44 (0) 7909 913 861

Dr Matt Thomas, Imperial College London
Tel: +44 (0) 207 594 2657 or +44 (0) 7952 910 734

Ifakara Health Research and Development Centre Tanzania:
Kija Nghabi +255-748-706110 (mob)
Dr Gerry Killeen +255-748-477118 (mob)

Wageningen University, The Netherlands
Dr Willem Takken, +31(0)317 484075
Dr Bart Knols +43 (0) 1 2600 28426, +43 (0)664 923 2875 (mob)

Pictures are available for free download at the
Photo credit: Hugh Sturrock.

Additional information:

1. Other means of malaria control include bednets, larval control, chemical insecticides, and anti-parasite chemotherapy. We hope that fungal biopesticides will complement these approaches (and indeed any others such as vaccines or GM mosquitoes which might become effective in the future). We are NOT arguing that fungal biopesticides should replace alternative control methods.

2. The biopesticide consists of fungal spores applied at ultra low-volumes in oil. After application, they are undetectable to the touch or by eye. The spores are inert until coming in contact with an insect.

3. Fungal biopesticides are already registered for agricultural use in Africa (e.g. for use against locusts, and marketed as Green Muscle), have passed environmental and human health safety testing, and are in industrial production. There they are comparable in cost to chemical insecticides. The cost in the malaria control context has yet to be determined but could compare well with chemical approaches.

4. While they have a much narrower host range than most chemical insecticides, fungal biopesticides are still likely to affect certain non-target insect species, but because they would be applied only the inside walls and ceilings of houses, they will only affect other nuisance household insects like flies and other biting insects.

5. The fungi are natural pathogens of insects. The spores germinate on contact with an insect and penetrate into it before proliferating throughout the insect. After insect death, the corpse sporulates (goes moldy or furry) and insects which contact such a corpse in turn become infected. Secondary transmission between adult mosquitoes is extremely unlikely because adults rarely spend time on the ground where corpses are.

6. Fungal control of mosquitoes has been previously attempted against mosquito larvae; what is new here is that this is targeted at adult mosquitoes. Other insect pathogens, such as some bacteria and viruses, could also be used as biocontrol agents against adults, but they need to be eaten by the insect and no reliable delivery system has been developed. In contrast, fungal spores just require contact, and they can be applied to surfaces such as bednets and walls where mosquitoes are known to rest.

7. It has been known for almost a century that malaria rates are far more sensitive to changes in adult mosquito survival than changes in larval survival, which is why residual indoor spraying proved so effective in the past.

8. The principal challenges for this approach are (i) attracting more funding, and (ii) long-term persistence of the biopesticide after application, and (iii) making the technology affordable and practical.

9. Malaria kills more than 1 million people/year in Sub-Saharan Africa, and causes 300-660 million clinical attacks/year globally.

10. Malaria is caused by protozoan parasites (single celled animals) and is transmitted between humans by mosquitoes. After mosquitoes have fed on people, they rest on walls and ceilings for some hours to digest their blood meals. This is where they were targeted with the fungus in the field trial in Tanzania.

11. There is a perception that there are health and environmental risks associated with chemical insecticides such as DDT. There is little evidence of such risks when chemical insecticides are used on bednets or indoor house spraying for malaria control.