Wednesday, January 14, 2009

Malaria Mosquito Lifespan Experiment

This at least is clever. It will not eradicate the disease, but if it can be made to work, it will slash the population. This then enhances and speeds the effect of other measures. It took generations to eliminate the endemic problem from Italy with the full support of the government. From that we learned that it could be done and gained an appreciation of how hard it is to drive an insect population to extinction.

Been able to enter an endemic district and initially halving the life span of the mosquito vector we surely decimate the infection rate allowing quinine to be more readily effective. This suggests that a district can be cleared much faster at a great saving of deployable resources.

The best use protocol must still be worked out and it is not the whole solution, but it smells like part of the solution. This is one thing at least that has been learned by science form the AIDs crisis. A combination of methods is very effective.

The decimation of indigenous populations in the Americas after Columbus was not caused by any one specific disease. It was caused by a succession of usually three separate infectious diseases in fairly rapid succession of a few years. The mathematics is inexorable. A serious epidemic will wipe out up to ninety percent of the population leaving a resistant residual population to rebuild. A later epidemic will hit the survivors on the same basis.

Thus a tribal population of perhaps ten villages totaling 2000 inhabitants is cut back perhaps to two villages of three hundred or so. A second infection passes through killing of the young and taking 70% of the adult population. You are now down to less than one hundred individuals, not all child bearing age and desperately looking to join another village.

A third epidemic would easily force the remnant into extinction. We have every reason to believe that this is what happened in the Americas.

Understanding this means that a protocol combination of three is likely enough to drive a biological problem to near extinction. It follows that a program of quinine, net exclusion and life span shortening will drive the mosquito to the edge of extinction which it should not recover easily.

Scientists hope to prevent malaria by cutting lifespan of mosquitoes
By Lauran Neergaard, The Associated Press

WASHINGTON - Old mosquitoes usually spread disease, so Australian researchers figured out a way to make the pests die younger - naturally, not poisoned.

Scientists have been racing to genetically engineer mosquitoes to become resistant to diseases like malaria and dengue fever that plague millions around the world, as an alternative to mass spraying of insecticides.

A new report Friday suggested a potentially less complicated approach: breeding mosquitoes to carry an insect parasite that causes earlier death.

Once a mosquito encounters dengue or malaria, it takes roughly two weeks of incubation before the insect can spread that pathogen by biting someone, meaning older mosquitoes are the more dangerous ones.

The Australian scientists knew that one type of fruit fly often is infected with a strain of bacterial parasite that cuts its lifespan in half.

So they infected the mosquito species that spreads dengue fever - called Aedes aegypti - with that fruit-fly parasite, breeding several generations in a tightly controlled laboratory.

Mosquitoes born with the parasite lived only 21 days - even in cosy lab conditions - compared with 50 days for regular mosquitoes, University of Queensland biologist Scott O'Neill reported in the journal Science.

Mosquitoes tend to die sooner in the wild than in a lab. So if the parasite could spread widely enough among these mosquitoes, it "may provide an inexpensive approach to dengue control," O'Neill concluded.

Theoretically, it could spread: This bacterium, called Wolbachia, is quite common among arthropod species, including some mosquito types - just not the specific types that spread dengue and malaria, the researchers noted. And Wolbachia strains are inherited only through infected mothers, with an evolutionary quirk that can help them quickly gain a foothold in a new population.

Next month, O'Neill's team begins longer studies in special North Queensland mosquito facilities that better mimic natural conditions to see how well the wMelPop strain persists as more mosquitoes are born, and what happens when they're exposed to dengue.

"By killing old mosquitoes, wMelPop could thus impact on dengue transmission," Pennsylvania State University specialists Andrew Read and Matthew Thomas concluded in an editorial accompanying the work, which they called "a major step."

It's possible that dengue viruses could evolve to incubate more rapidly if their mosquito hosts die younger, they noted, although that likely would be less of a problem than today's insecticide resistance.

Still, "determining whether it can remove enough infectious mosquitoes to be useful will be a challenge," the duo cautioned.

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