A new study, reported in the open-access journal PLoS Neglected Tropical Diseases, has shown that two bacteria – one of them genetically modified – could help reduce or even eliminate the deadly disease African trypanosomiasis, also known as sleeping sickness.
This image shows a tsetse fly. Image credit: Oregon State University.
African trypanosomiasis is caused by the parasite Trypanosoma brucei rhodesiense carried by the tsetse fly. It infects 30,000 people in sub-Saharan Africa each year and is almost always fatal without treatment.
In the new study, scientists evaluated the potential for success of a new approach to combat the disease – creating a genetically modified version of the Sodalis bacteria commonly found in the gut of the flies that carry the disease, and using different bacteria called Wolbachia to drive the genetically modified version of Sodalis into fly populations. When that’s done, the genetically modified version of Sodalis would kill the disease-causing trypanosome parasite.
According to the results, the scientists say this should work – and could offer a model system for other tropical, insect-carried diseases of even greater importance, including dengue fever and malaria.
“There are a few ‘ifs’ necessary for this to succeed, but none of them look like an obstacle that could not be overcome,” said lead author Dr Jan Medlock from Oregon State University.
“If everything goes right, and we are optimistic that it will, this could be enormously important. There’s a potential here to completely solve this disease that has killed many thousands of people, and open new approaches to dealing with even more serious diseases such as malaria.”
Some of the ‘ifs’ include: the transgenic Sodalis has to be reasonably effective at blocking the parasite, at or above a level of about 85 percent; the Wolbachia bacteria, which has some effect on the health of flies affected with it, must not kill too many of them; and the target species of fly has to be a majority of the tsetse flies in the areas being treated.
The study shows that dealing with all of those obstacles should be possible. If so, this might spell the end of a tropical disease that has plagued humans for hundreds, possibly thousands of years.
African trypanosomiasis causes serious mental and physical deterioration – including the altered sleep patterns that give the disease its name – and is fatal without treatment. It’s still difficult to treat, and neurologic damage is permanent. Past efforts to control the disease, including insect traps, insecticide spraying, and use of sterile insects have been of some value, but only in limited areas and the effects were not permanent.
“The strength of the new approach is that once the process begins it should spread and be self-sustaining – it should not be necessary to repeatedly take action in the huge geographic areas of Africa. Due to some genetic manipulation, the flies carrying the Wolbachia bacteria should naturally increase their populations and have an inherent survival advantage over conventional tsetse flies,” the scientists said.
“As the flies carrying transgenic bacteria continue to dominate and their populations spread, trypanosomiasis should fairly rapidly disappear. Whether the mechanism of control could wane in effectiveness over time is an issue that requires further study.”
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Bibliographic information: Medlock J et al. 2013. Evaluating Paratransgenesis as a Potential Control Strategy for African Trypanosomiasis. PLoS Negl Trop Dis 7 (8): e2374; doi: 10.1371/journal.pntd.0002374
