Housefly genome offers clue to human sickness

The fly can carry some 100 illnesses, including one that can blind. By comparing its DNA with that of a fruit fly, the US team at Cornell University pinpointed the genes that make houseflies immune to the pathogens they harbour.

They also found unique code that helps the fly to dissolve waste, such as faeces. Information about these genes could help us to handle human waste and improve the environment, Dr Jeff Scott and colleagues told the journal Genome Biology.

Shoo-fly Houseflies are ideally suited to spreading disease. They have regular contact with carcasses, rubbish and other septic matter containing bacteria, viruses and other "nasties" such as tapeworms. They enjoy some of the same food that we do, and because they are very good at evading our detection, they get plenty of opportunities to land on it (as well as on us).

It is believed that they carry so many pathogens because they feed on liquid or semi-liquid matter - often faeces. Their constant food intake, in turn, means that they need to evacuate large amounts of faeces - along with any pathogens they are carrying - whenever they land for more than a few seconds. Unlike us, they don't get sick from this dirty lifestyle. Dr Scott and his team were intrigued to find out why and to see if it might be possible to utilize this skill for mankind's benefit.

They sequenced the genomes of six female houseflies, creating a 691 Mb long sequence. They then compared it with the 123 Mb genome of the fruit fly, Drosophila melanogaster, to find which parts of DNA were unique to housefly, and could be candidates for further study.

The housefly had many more immune genes than Drosophila. Its immune genes were also more diverse - presumably to offer it protection against the numerous pathogens it carries.

Prof David Conway of the London School of Hygiene & Tropical Medicine said: "Although we often think of houseflies as just a nuisance, they can transmit many pathogenic bacteria to people and contribute significantly to disease in poor communities where sanitation is limited.

"It is great to see this analysis of the genome sequence, in particular its comparison with the genomes of fruit flies which have been more intensively studied until now.

"Many other flies transmit important human diseases and hopefully this work will encourage further genome analyses of these disease vectors, and comparisons between them.

The genome of the tsetse fly, which transmits sleeping sickness in Africa, was published a few months ago - although it feeds on blood it is more closely related to the housefly than it is to mosquitoes. There are many other vectors of neglected diseases that could be better understood if we had more comparisons of their genomes", Dr. David said.