Stripping Down Science by Chris Smith, Dr Christorpher Smith Page A

recording the electrical activity from the individual nerves inside the fruit fly antennae as the insects were exposed to 100 different chemicals and odours in turn, including substances known to be produced byhumans and the bacteria that live on human skin, it was possible to work out what contribution each gene makes to the smell-detecting repertoire of a mosquito.
    This means that researchers now know which classes of chemicals mosquitoes can respond to and which ones are likely to be key targets in developing novel repellents. For instance, 27 of the receptors studied responded particularly strongly to compounds found in human sweat. Now they’ve been identified, research is focusing heavily on how these receptors work, how they interact with the odour molecules they detect and how best to block them or, paradoxically, activate them.
    â€˜We’re screening for compounds that interact with these receptors,’ says John Carlson, one of the other scientists involved in the study. ‘Compounds that jam these receptors could impair the ability of mosquitoes to find us. Compounds that excite these receptors could help to lure mosquitoes into traps or repel them. The best lures or repellents may be cocktails of multiple compounds. The world desperately needs new ways of controlling these mosquitoes, ways that are effective, inexpensive, and environmentally friendly.’

    FACT BOX
    Turning mosquitoes into flying vaccinators
Nuisances as mosquitoes are, and desperate as scientists are to disable them, researchers have nonetheless also been sizing them up as mobile hypodermics capable of delivering a flying vaccination service. The work is based on the premise that, every time they take a blood meal, female mosquitoes first inject their saliva, containing anticoagulants and immune-evading agents, around the blood vessel puncture site. This is what provokes the itchy inflammatory aftermath but is also responsible for transmitting infectious agents like malaria, which the mosquito regurgitates into the wound when it feeds.
Shigeto Yoshida, from Jichi Medical University in Japan, 44 reasoned that it ought to be possible to exploit this unpleasant aspect of the insect’s behaviour in a beneficial way.He set about genetically modifying Anopheles mosquitoes to make them produce in their saliva a protein called SP-15, which is critical for the spread of another major disease-causing parasite called Leishmania . Mice bitten repeatedly by these modified mosquitoes developed antibodies to SP-15, which other researchers have shown can protect against Leishmania transmission. ‘Following bites, protective immune responses are induced, just like conventional vaccination but with no pain and no cost,’ says Yoshida. ‘What’s more, continuous exposure to bites will maintain high levels of protective immunity, through natural boosting, for a lifetime.’
The next step will be to test whether mice vaccinated by these mosquitoes really can be protected from Leishmania infection in future. The odds are that it should work, because the same SP-15 protein has been successfully tested as an experimental vaccine previously. But whether this flying vaccinator technology will take off in general and for other types of vaccines is another matter. Some may feelslightly stung by the idea of a natural and uncontrolled vaccination system delivering unmetered drug dosages and boosters indiscriminately.
This sentiment is pre-empted by Yoshida himself in his paper describing the work in the journal Insect Molecular Biology : ‘The concept of a “flying vaccinator” transgenic mosquito is not likely to be a practicable method of disease control, because “flying vaccinator” is an unacceptable way to deliver vaccine without issues of dosage and informed consent against current vaccine programs. These difficulties are more complicated by the issues of public acceptance to release of transgenic