Frog 'key to mosquito repellents'
[BBC 2006-02-22]

[Photo] The malaria parasite is spread by mosquitoes

A bottle-green Australian frog may hold the key to future mosquito repellents, a study says.

A University of Adelaide team found the secretions of the dumpy tree frog are effective at warding off mosquitoes.

Researchers found mice given the secretions remained bite-free for four times longer than those not, the Biology Letters journal reported.

But experts said such repellents would only have a limited effect in fighting malaria, which is spread by mosquitoes.

Researchers chose to investigate frogs because previous research had uncovered that their secretions can act as powerful painkillers and hallucinogens.

The team also found two other Australian species - the desert tree frog and Mjoberg's toadlet - released mosquito repellent odour from their skin, although their secretions were not tested on mice.

In the study, mice given the secretions from the dumpy tree frog remained bite-free for around 50 minutes compared to 12 minutes for an untreated group.

However, mice given Deet, the chemical that is typically used in commercial mosquito repellents, were protected for up to two hours.

The researchers said the frog secretions should not yet be considered as an alternative to Deet, which was originally formulated for the US army after WWII.

But they said: "The discovery highlights the potential of the unsung properties of amphibian skin.

"Many aspects of frog chemical ecology remain unexplored."

However, a leading expert suggested the impact on fighting malaria, which is responsible for one million deaths a year, would be limited.

Dr Nigel Hill, a disease control expert at the London School of Hygiene and Tropical Medicine, said repellents had "limited, but interesting" uses for controlling malaria.

"Afghan refugee camps have found the use of repellent soap to reduce malaria to some degree."

But he said some of the plant-based repellents which had been tried were more practical than frog-based ones because the plants were more readily available.