A decade long effort by Yale scientists has unlocked the genetic code of the deadly tsetse fly and provides clues to eradicating this African scourge.
The tsetse fly’s bite transmits sleeping sickness, a parasitic disease that drives victims to insanity before they sink into a coma and ultimately die. While there are currently fewer than 10,000 confirmed cases per year, the disease tends to run in epidemics as evidenced as recently as 1998 when there were an estimated 300,000 cases of sleeping sickness reported. Treatment for the disease is lengthy and difficult for the victim, but without treatment death rates are 100%. In addition to the cost in human life, tsetse flies also carry nagana, a disease that weakens and kills cattle and has left entire regions of Africa bereft of livestock.
Decoding the genome of the Glossina morsitans, one of many tsetse species, was especially challenging due to a number of reasons, not the least of which is the unusual biology of the tsetse fly. They are the only insects that nurse their young, and give birth to a single larva. “Tsetse biology is just freaky,” said Leslie B. Vosshall, an insect neurobiologist at Rockefeller University. Most fly species lay hundreds of eggs in rotting fruit or carcasses relying on sheer numbers for larval survival. Tsetse females give birth to a single larva that weighs nearly as much as she does. While gestating, the larva nurses on a milk gland that blends fats with water, creating proteins, passing on hormones and making it possible to digest iron. “It’s an example of convergent evolution,” said Geoffrey Attardo, a member of the Yale team and co-author of the study.
Researchers found several spots on the genome they hope will lead to better insecticides or repellants. In fact, a gene call ladybird late, controls milk production in the fly. When researchers disabled it, the larvae starved. Chemicals with the same properties, once discovered, could be sprayed on cattle and picked up by the feeding flies causing them to die out. Other possible defenses could include tweaking genes to make the fly reject the parasites that cause sleeping sickness, or developing chemicals that block the fly’s ability to smell humans.