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Mosquitoes begin to get wise to anti-malaria nets

By Catholic Online (NEWS CONSORTIUM)
September 20th, 2012
Catholic Online (www.catholic.org)

Insects are a highly adaptive form of organism, displaying at times an almost human-like intelligence. This is especially true if there is a chain in their food chain. Two African villages using mosquito nets began to notice a marked difference in the mosquitoes' biting habits in order to avoid the barriers.

LOS ANGELES, CA (Catholic Online) - In a French study, mosquito behavior before and after was gauged in all households in two villages in Benin were given insecticide-treated nets.

The report, appearing in the Journal of Infectious Diseases, French researchers found that mosquitoes seemed to change their hours of "peak aggression" from 2 a.m. or 3 a.m. to around 5 a.m., three years after nets were put up.

In one village, the proportion of mosquito bites inflicted outdoors rose.
 
Insecticide-treated bed nets are a vital weapon in the global fight against malaria. The disease is borne by parasite-carrying mosquitoes and kills more than 650,000 people a year, according to the World Health Organization.

Outdoor bites accounted for 45 percent of all bites at the outset, but rose to 68 percent one year later and 61 percent after three years.

This trend is "worrying since villagers usually wake up before dawn to work in crops, and as such they are not protected by mosquito nets," senior researcher Vincent Corbel, of the Montpellier said in an email.

Scientist stress that the report is limited in scope. The results, after all come from just two villages in one country. "We cannot extrapolate to a wider geographical area and/or a different entomological context," Corbel warned.

A malaria researcher not involved in the study said the results of the study should be interpreted with caution due to the difficulty in getting reliable measures of mosquito "biting behavior" over time.

In Corbel's study, the team used the standard way of gauging mosquito activity, the "human landing catch" meaning that a mosquito collector lets the pest land on his skin and then catches it.

Mosquito nets have been credited with spurring big drops in malaria deaths. For every 1,000 children protected by an insecticide-treated net, five to six lives would be saved every year, according to a report for the Cochrane Collaboration.

Malaria cases have started to climb again in certain African countries in recent years, Corbel said. Experts have mainly been concerned about mosquitoes' growing resistance to the insecticides used in bed nets and for indoor spraying.

"Long-lasting insecticidal nets were developed to protect people at night when they are sleeping," Corbel says, noting that if mosquitoes shift to early morning and outdoor biting, the nets might not be enough to keep malaria under control.

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