(left) Creative Commons; (Right) The collaboration of Wiegandt and Bigelow
The researchers genetically engineered a fungus that attacks the malaria parasite in the mosquito. They hope the fungus spores, applied to the walls of houses or traps mosquitoes could help stop the spread of the disease in a manner respectful of the environment.
The fungi that attack insects are present in soils around the world and are used in gardens, greenhouses and open fields to control agricultural pests. In 05, scientists showed that stem from two different fungi, Beauveria bassiana and Metarhizium anisopliae could attack the mosquitoes that spread malaria. When fungal spores come in contact with the exoskeleton of the mosquito, they bore their way into the equivalent of the hemolymph of the insect-Blood, where they grow, eventually killing the mosquito.
But fungi take about 2 weeks to kill insects. "They want to kill slowly, extracting as much nutrients as possible so they can produce more spores," says Raymond St. Leger, an entomologist at the University of Maryland, College Park. Because it takes only 12 to 14 days for the malaria parasite to mature into its infectious form in the mosquito, an insect often has time to spread the parasite before fungal infection has killed everything, especially if the mosquito is exposed to the fungus several days after he picks up parasite.
St. Leger and his colleagues originally created a genetically modified version of the fungus M. anisopliae that through the insertion of a specific neurotoxin to insects, kills mosquitoes quickly but a quick death is also a disadvantage. it can lead to mosquitoes that are resistant to the fungus, because the resistant insects are the only surviving long enough to reproduce
strains. now St. Leger and his colleagues designed M. anisopliae to block the malaria parasite from developing inside the infected mosquito. online today Science They describe the insertion of different combinations of three different genes in the fungus to block the malaria parasite from entering the salivary glands of the mosquito. (Parasites from the salivary glands to infect new hosts when an infected mosquito bites a new victim.) A gene codes for a peptide of a short piece of a protein called SM1 that resembles the parasite parasite protein used to penetrate the salivary glands. Copies of SM1 produced by the fungus block the path of the parasite in. Another gene code added to a portion of a human antibody that binds to parasites and causes them to regroup. A third is an antimicrobial protein called scorpine, it has been found in scorpions that kills the malaria parasite.
When the researchers sprayed the strains of fungi spores genetically modified mosquitoes in the lab, the spores will not kill insects faster than the normal fungus has. But they will significantly reduce the number of parasites in the salivary glands of mosquitoes: Six days after receiving the spores of genetically modified strains, mosquitoes had 98% fewer parasites in their salivary glands than for those treated with the normal fungus .
And genetically modified fungus acts quickly. After giving mosquitoes a blood meal infected with malaria, the researchers waited 11 days before spraying some with normal fungal spores and other improved with spores. Two days later, 86% of fungus without mosquitoes could transmit malaria, could 72% of insects infected with the normal fungus, but only 20% of mosquitoes exposed to transgenic fungus could.
The results are impressive, says Marit Farenhorst who studies fungi insect attacking In2Care, a start-up in Wageningen, The Netherlands. "If you're a little late to get the infected mosquito in the field, you can still be in time to influence the transmission of malaria," she said. "It's like the vaccination of the mosquito." The main drawback of the approach, said Farenhorst, is that fungal spores survive only a few months when applied on walls or other surfaces. It is currently impractical and expensive to have to keep reapplying spores. But several teams are working on better ways to apply the spores and keep them alive, she said.
Although St. Leger acknowledges that the widespread suspicion of genetically modified organisms could make it harder to persuade people to apply the fungus in their homes, he said the approach is extremely low risk: The strain of fungus modified scientists only infects mosquitoes, genes that they recognize human malaria inserted, and the genes are only activated once the fungus is within the mosquito. None of the genes give the fungus a survival advantage on wild strains that are common in soil, he said. Yet St. Leger said, the completion of the relevant safety tests take several years.
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