Tuesday, November 4, 2008

Big Mosquitoes are Safer Mosquitoes

mosquito on human arm
photo from the Michigan DNR
from a news release of University of Illinois at Urbana-Champaign , "Smaller mosquitoes are more likey to be infected with viruses causing human diseases," Nov 3, 2008

An entomologist at the Illinois Natural History Survey says smaller mosquitoes are more likely to be infected with viruses that cause diseases in humans.

Barry Alto, Ph.D., Director of the Medical Entomology Program at the Illinois Natural History Survey, and several colleagues, fed mosquitoes blood with dengue virus and later tested them for infection. The researchers painstakingly took into account the size of each mosquito by measuring the length of their wings. Smaller-sized mosquitoes had higher infection and potential to transmit dengue virus than larger individuals. Other components, such as adult longevity, host preference, and feeding frequency, that determine a mosquito's vectoring ability still need to be taken into account in future studies.

The Asian tiger and yellow fever mosquitoes are the two main transmitters of dengue virus, the mosquito-borne virus of greatest importance to human health. Both of these mosquitoes are found throughout the world including the U.S. The ferocious tiger mosquito invaded Illinois in the 1990s. Now researchers have shown that only slight differences in the body sizes of these mosquitoes drastically alter their potential to transmit viruses causing human disease.

What's more surprising is that the effects were consistent for the two mosquito species.

Results of this study have important implications for mosquito control strategies and evaluation of disease risk for dengue. Competition among the larvae of container-breeding mosquitoes results in smaller sized adults. However, control strategies (e.g., larvacides) release surviving larvae from competition, resulting in the production of larger adult mosquitoes. Thus, a benefit of control strategies may be the production of larger, less competent adult mosquitoes in terms of infection. These results have the potential to provide information on disease risk and aid in control efforts of the diseases that mosquitoes transmit.

The Medical Entomology Program of the Illinois Natural History Survey originated out of concern for container mosquitoes. In recent times the program has invested much of its efforts towards addressing West Nile virus in Illinois as well as a program on encephalitis prevention.

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