Electronic mosquito repellents just don't do it!

Scientists in Iran have found that electronic mosquito repellents which are marketed as being able to drive insects away with high-pitched sounds do not work.

A team led by Dr Ahmadali Enayati, from the Mazandaran University of Medical Sciences in Iran, analyzed 10 studies conducted in North America, Russia and Africa.

All were field-based studies which occurred in a natural setting rather than a laboratory.

Malaria which is contracted from mosquito bites affects more than 250 million people worldwide and results in over a million deaths each year; it is particularly prevalent in sub-Saharan Africa.

No vaccine against malaria is available.

Electronic mosquito repellents (EMRs) are battery-powered hand-held devices that emit a high frequency buzz almost inaudible to the human ear which claim to repel mosquitoes within a range of up to 2.5 metres, both indoors and outdoors.

Mobile phone companies too also market a ring tone that is said to deter mosquitoes.

The devices target female mosquitoes, because they are the ones which bite and are supposed to mimic the flight sound of males; it is thought as they mate only once in their lives, this may repel the female insects once they have mated.

The noise is also said to sound like bats, which prey on mosquitoes.

The ten trials assessed the number of mosquitoes landing on the bodies of human volunteers and the scientists found in all ten there was no difference in the number of mosquitoes found on the bare body parts of the human participants with or without an EMR.

The scientists say EMRs have no effect on preventing mosquito bites and there is no evidence to justify them being marketed to prevent malaria infection.

According to the authors despite 30 years of scientific skepticism and a successful prosecution in the 1980s of EMR marketers under the UK Trade Description Act, worldwide marketing of the devices has not been dented.

This say the researchers is a concern, because consumers do not use other protective methods that are proven to work.

They suggest other available options should be used such as mosquito repellents formulated as pills, ointments, lotions and sprays, and insecticide-soaked bed nets which kill female mosquitoes on contact or repel them from the house during the biting hours, from dusk to dawn.

The paper was published by the Cochrane Library, part of the Cochrane Collaboration, a UK-registered charity which specialises in research reviews.