Patrick Guilfoile: Putting sleeping sickness to bed
Sleeping sickness has long been a human scourge. The disease is caused by a parasite called a trypanosome, which is transmitted by the bite of a tsetse fly. Sleeping sickness is endemic to Central Africa, where 70 million people are potentially at risk for infection, and an estimated 20,000 cases occur each year.
The parasite also causes disease in cattle, resulting in three million animal deaths and a billion dollars or more of economic loss each year.
Sleeping sickness is insidious. Within a few weeks after a bite, a red sore develops around the site of infection. Weeks to a year later, fever, swelling, headaches, fatigue, and weight loss occur.
Eventually, daytime sleepiness, confusion, and personality changes occur as the parasite damages the brain. Without treatment, death typically occurs within several years.
Current treatments for sleeping sickness have serious side effects, and no vaccine is available.
Therefore, methods of control are focused on eliminating the tsetse flies through trapping, insecticide spraying, and the release of sterile male flies. (This technique works because most female tsetse flies mate only once during their lifetime.)
However, current methods of control have limitations and new methods of controlling tsetse flies are needed in order to eliminate the disease.
Therefore, researchers from 81 institutions in Africa and across the globe recently sequenced the genome of the tsetse fly, in order to better understand this insect, with the hopes of developing improved methods of control.
The sequencing work identified odor and taste receptors that may facilitate the development of better traps.
For example, tsetse flies have many receptors for sensing carbon dioxide, which likely helps them find humans or cattle.
Therefore, traps that take advantage of this keen ability to detect carbon dioxide may be more effective than existing traps.
Tsetse flies are odd insects in many ways- they give birth to live young, and they produce milk for nurturing their larvae.
The milk production by tsetse flies could be another avenue for control. If milk production is eliminated in the flies, the larvae don’t develop.
Researchers found a master gene that regulates milk production in tsetse flies, and this gene could be another target for reducing their population.
Tsetse flies take in enormous blood meals- an amount of blood nearly equivalent to their weight in one sitting. Researchers identified a number of genes that produce pores which aid in the excretion of water. Because blood contains such large amounts of water, these pores are critical for efficient feeding.
Therefore, finding chemicals that target these pores could be an effective means of killing these insects.
Sleeping sickness continues to be a deadly disease in a wide swath of central Africa.
This newly reported sequence of the tsetse fly offers hope that we can someday put this malady to rest.
More information is available in the Article by the International Glossina Genome Initiative “Genome sequence of the Tsetse fly (Glossina morsitans): vector of African trypanosomiasis” in Science Vol. 344: pages 380-386, April 25, 2014.
PATRICK GUILFOILE has a doctorate in bacteriology and is the associate vice president at Bemidji State University.