The next generation of insect repellents could be in the pipeline with research from the U.S. suggesting seven possibilities.
Researchers from a government mosquito and fly research unit in Florida say they have identified seven likely candidates for the next mosquito repellents and some of them promise to provide longer protection.
Repellents currently available which are effective often contain DEET (N,N-diethyl-meta-toluamide), which was also originally developed for military use in 1946.
DEET has a good safety record, but some people are concerned about its use with children and pregnant women and the Environmental Protection Agency (EPA) says that DEET has been implicated in seizures among children, but there is not enough information to confirm it as the cause of the incidents.
According to the EPA one-third of the U.S. population uses products containing DEET every year to repel biting insects such as ticks and mosquitoes.
Ticks and mosquitoes, which are becoming an increasing problem in many parts of the world, can cause and spread a range of diseases - among them encephalitis, Lyme disease, Rocky Mountain spotted fever, malaria, Dengue Fever, yellow fever, Rift Valley fever, Ross River Fever, St. Louis encephalitis, West Nile virus, Japanese encephalitis, La Crosse encephalitis, Chikungunya and Eastern equine encephalitis and Western equine encephalitis.
The researchers say though DEET repellents offer broad-based protection from a variety of insects, mosquitoes continue to spread diseases such as malaria and some mosquitoes can bite through an application of DEET.
While tests of the new chemicals have produced "phenomenal" results, research chemist Dr. Ulrich R. Bernier says the new repellents are unlikely to be available commercially for a few years.
Dr. Bernier says early tests were promising, with some chemicals repelling mosquitoes for as long as 73 days and many working for 40 to 50 days, compared to an average of 17.5 days with DEET.
The research focused on a type of chemical known as N-acylpiperidines and of the initial 34 candidates a process of elimination left seven which satisfied concerns about toxicity and production costs.
The tests were carried out on cloth treated with the chemicals and then placed on the arms of volunteers - now tests will be carried out using the seven most promising compounds directly on the skin.
The research was funded by the Defense Department and aimed to discover why repellents work and to find more effective ways to discourage disease-carrying insects.
It is published in the current edition of the Proceedings of the National Academy of Sciences.