Virus May Act as "Evolution-Proof" Biopesticide Against Malaria

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A naturally occurring virus in mosquitoes may serve as a "late-life-acting" insecticide by killing older adult mosquitoes that are responsible for the bulk of malaria transmission. The researchers from Johns Hopkins University and the Johns Hopkins Malaria Research Institute in Baltimore detail their findings in the August 2010 issue of the Journal of Virology.

Malaria infects hundreds of thousands of people each year and is the cause of over a million deaths worldwide. Insecticides are one of the main strategies currently used to control malaria transmission, however, evolving resistance to such therapies continues to impact such efforts. "Late-life-acting" insecticides (LLAIs) are now being examined as a new approach for controlling malaria as they selectively kill older mosquitoes that spread the disease, while younger mosquitoes survive just long enough to reproduce.

"Reproduction allows for relaxation of evolutionary pressures that select for resistance to the agent," say the researchers. "If resistance alleles exert fitness costs, there are theoretical scenarios under which resistance is not expected to evolve, leading some to provocatively term LLAIs as 'evolution-proof'."

Densonucleosis viruses (or densoviruses [DNVs]) are naturally occurring parvoviruses that have been identified in multiple mosquito species. Some DNVs typically infect during the larval stage and are lethal, however, in this study researchers suggest that the Anopheles gambiae densovirus (AgDNV) may infect at low levels during early life and replicate to lethal levels at adult age. Analysis following infection showed that although AgDNV levels increased modestly during larval development they still replicated slower resulting in significantly decreased virus levels during this stage. Additionally, virus levels greatly increased in 7-to-10-day-old adults.

"Ultimately, we expect that a properly engineered LLAI AgDNV can be deployed in the field to significantly modulate malaria transmission," say the researchers.

Reference: X. Ren, J.L. Rasgon. 2010. Potential for the Anopheles gambiae densonucleosis virus to act as an "evolution-proof" biopesticide. Journal of Virology, 84. 15: 7726-7729.

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