Washington, U.S.A. — Given the number of Wile Nile virus (WNv) cases, including 26 deaths, it is important to focus attention on mosquito management methods that are the most effective and do not introduce additional short- and long-term public health hazards with the use of toxic pesticides, public health advocates say.

It is understandable that local, state, and federal officials want to act decisively, but that does not mean that the widespread use of hazardous pesticides is the best course of action, according to Beyond Pesticides, a national information and advocacy organization on pesticides and alternatives based in Washington, DC.

According to Beyond Pesticides’ executive director, Jay Feldman, “Communities that are most successful and smart about mosquito control engage in aggressive efforts to reduce and eliminate mosquito breeding areas in standing water around homes and buildings and throughout the community.”

Mosquito breeding can take place in stagnant water, from very small to larger pools –bottle caps, discarded automobile tires, planters, containers, rain gutters, drains, or under piles of leaves.

The widespread spraying of toxic pesticides (typically chemicals known as synthetic pyrethroids, organophosphates, or other nervous system poisons) does not provide a long-term sustainable solution to mosquito control.

“It has been shown that spraying pesticides that target adult mosquitoes is the least effective strategy, as well as the most risky response, since the pesticides used are linked to numerous adverse health effects, including respiratory inflammation, headaches, nausea, cancer, endocrine disruption, and other serious chronic diseases,” said Nichelle Harriott, staff scientist at Beyond Pesticides.

According to experts, the threat of WNv is best managed through an integrated program that does not expose vulnerable populations to pesticides, including children, pregnant women, the elderly and people with compromised immune or nervous systems.

The most effective program to protect the public from WNv focuses on removing breeding areas, stopping mosquitoes at the larval stage, and mass public education on prevention and precaution.

Beyond Pesticides advises communities to adopt a preventive, health-based mosquito management plan and has several resource publications on the issue, including the Public Health Mosquito Management Strategy: For Decision Makers and Communities, found online at www.beyondpesticides.org/mosquito.

What people can do

Clean up – ensure waterways are clear of debris; eliminate pooled or stagnant waters from debris, containers, drains, and pools.
Natural Predators – Use indigenous fish populations, like bluegills or minnows, to eat mosquito larvae in shallow waters and ornamental pools. Copepod crustaceans can also be used to eat mosquito larvae in ditches, pools and other areas of stagnant water.

Least-toxic Pesticide Options

Use Bacillus thuringiensis israelensis (Bt), a biological larvicide that prevents mosquitoes from developing into breeding, biting adults, in standing waters that cannot be drained.

Behavior Modification – wear long sleeves and long pants/skirts, and use least-toxic mosquito repellent when outdoors. Avoid being outside at dusk when mosquitoes are most active.

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Oxford, England — Oxitec scientists have reported the creation of a new flightless strain of the Asian tiger mosquito, Aedes albopictus. The breakthrough, reported in the journal PLoS Neglected Tropical Diseases, could help stop the spread of this dangerous and invasive pest.

The Asian tiger mosquito is a serious nuisance biter, but is also capable of transmitting dengue fever, Chikungunya, West Nile Virus and a host of other diseases. In the last few decades it has spread throughout the world and is now established in many regions, including Europe and the US, where it is becoming both an extremely bothersome pest and an increasing health concern.

Dr. Randy Gaugler, Director of the Center for Vector Biology at Rutgers University in New Brunswick, USA explains the threat. “The Asian tiger mosquito is an extremely aggressive biter prominent in the global surge in new and emerging vector-borne diseases. The public health threat from this mosquito, particularly with regard to transmission of dengue and chikungunya, is of concern to health professionals because there are no vaccines or chemo-prophylaxis to treat infection. Suppressing the mosquitoes that transmit the viruses is the only available approach. Conventional control strategies against this species have been moderately effective at best. A new paradigm is needed.”

The Asian tiger mosquito is an extremely difficult pest to control: conventional methods rely on chemical pesticides which not only harm other insects but are increasingly ineffective as mosquitoes develop resistance.

Now, an Oxitec team led by Dr Genevieve Labbe has pioneered a new approach. The team has genetically modified the mosquitoes with a ‘flightless’ gene so that the females are unable to fly. Oxitec releases male mosquitoes carrying the flightless gene: male mosquitoes can’t bite or spread diseases, and when Oxitec males mate with wild females, their flightless daughters are unable to feed or reproduce, and soon die. Successive releases will lead to a rapid reduction in the overall population of these mosquitoes in an area.

Commenting on the breakthrough, Oxitec Chief Scientific Officer Dr Luke Alphey said:

“We believe this is an intelligent response to this invasive pest. These mosquitoes and their breeding sites are hard for humans to find, which limits the effectiveness of conventional control methods. So instead we are harnessing the natural drive of a male mosquito to seek out a female. It’s not only an effective strategy but an environmentally sound one too: the mosquitoes only mate with their own species so, in contrast to pesticides, non-target insects are not harmed. Removing this mosquito would cause minimal environmental disruption, not least because it is a very recent invasive species in most areas.

The flightless mosquito strain is an adaptation of Oxitec’s genetically ‘sterile’ mosquitoes, which have already been successfully demonstrated in Grand Cayman and Brazil, reducing target populations of the dengue mosquito, Aedes aegypti.

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A new study from Senegal has experts worried about the spread of malaria through mosquitoes. The study has shown that mosquitoes can form a resistance to the insecticide used in mosquito nets.

Researchers studied the Senegalese village of Dielmo, over a span of years from 2007 to 2010. This documented the Malaria morbidity both before and after the 2008 distribution of long-lasting insecticide bed nets, a leading method in preventing malaria. Though some experts say the study was too small to draw conclusions, but the findings are troubling.

The study shows that mosquitoes may be forming a resistance to the insecticide. While just three weeks after the net introduction, there was a short-term decline in malaria attacks, the proportion of mosquitoes genetically resistant to a type of pesticide rose from 8 percent to 48 percent.

In 2010, the pesticide Deltamethrin, which is recommended by the World Health Organization for bed nets, was genetically resisted by 37 percent of Anopheles gambiae mosquitoes, the principal vectors for malaria in Africa.

This led to a raise in malaria attacks back to high levels, for the last few months of the 2010 study period. In fact, the rate of attacks was even higher amongst older children and adults than it was before the bed net introduction. According to the study, this is possibly related to a reduced immunity among these age groups.

According to the Center for Disease Control, in 2008 there were an estimated 190 to 311 million cases of malaria worldwide, causing 708,000 to 1,003,000 deaths. Most of these deaths occurred in young children from sub-Saharan Africa.

“Strategies to address the problem of insecticide resistance and to mitigate its effects must be urgently defined and implemented,” said the researchers in study.

Image Courtesy of  http://www.flickr.com/photos/gatesfoundation/

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