News / Science & Technology

Sex Matters for Sleeping Sickness Microbes

Dead tsetse flies are seen in a laboratory run by the International Livestock Research Institute in Ghibe Valley, 115 miles southwest of Addis Ababa, Ethiopia, June 1, 2002. (AP Photo/Sayyid Azim)
Dead tsetse flies are seen in a laboratory run by the International Livestock Research Institute in Ghibe Valley, 115 miles southwest of Addis Ababa, Ethiopia, June 1, 2002. (AP Photo/Sayyid Azim)

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Joe DeCapua
Scientists are keeping a close eye on the mating habits of microscopic organisms, including those that cause African sleeping sickness. They say what happens between two parasites can have major consequences for humans


Researcher Wendy Gibson said when it comes to single-cell parasites known as trypanosomes, sex matters. They had once been thought to reproduce by splitting in half. But scientists say they have a sex life. 

“This is important because if they can mate, it means that they can swap genes around. For example, if you’ve got a strain of parasite that’s resistant to a drug and it mates with one that isn’t, then it can swap that gene into the one that’s sensitive to the drug. And then, of course, you’ve got a new parasite, effectively, that is also resistant to the drug. That’s dangerous,” she said.

Gibson is professor of protozoology at the University of Bristol.

“Sleeping sickness is a very nasty disease. It’s carried by tsetse flies in tropical Africa. And now, fortunately, the numbers, as recorded by the World Health Organization, have dropped to less than 10,000 recorded cases. But years ago it used to really devastate large populations,” she said.

She explained how the illness got its name.

“It’s called sleeping sickness because the parasite gets into the brain and causes people to go into a sort of semi-comatose state. So that they just appear to be sleeping all the time. And that stage of the disease you can only treat with some very unpleasant drugs. One of them is based on arsenic. So you can imagine that that doesn’t do you any good”

Sleeping sickness has been on the decline due to early diagnosis, thorough treatment and better control of the tsetse fly population. That’s good news. But Gibson said that a resurgence is always possible.

“A colleague once described sleeping sickness to me as the sleeping dragon. It never goes away because the problem is that there are animal reservoirs of the disease. So even if you haven’t got humans with the disease in an area, it may still be circulating in animals, for example, cattle or wild animals. And of course the tsetse fly is feeding on those in keeping that cycle of transmission going. And it may then, if you’re unlucky, transfer back into the human population,” she said.

Gibson said it’s important to understand sexual reproduction in microbes.

“It’s one of the reasons why we’re worried about the next influenza outbreak because influenza is caused by viruses, but they also recombine. OK, it’s not the same sexual reproduction process as we get in these parasites, but it’s the same intrinsic mechanism that you’ve got recombination of genes. And, of course, with flu, you get new recombinant strains. We don’t know how virulent they are and what kind of disease they’ll cause and how quickly they’ll spread.”

The study of mating microbes helps explain how diseases spread and how new strains are formed. That’s why what’s happening in Uganda is being closely watched.

“You’ve got in the north of the country the West African form of the disease and in the southeast you’ve got the East African form. The East African form has been spreading northwards. And one of the worries is that it will overlap with the West African form of the disease. Now, if those two parasites then mate together, obviously, we’re worried that they’ll create some sort of superbug that maybe cause more serious disease,” said Gibson.

Trypanosomes are part of a group of organisms known as protozoa. They also include microbes that cause such illnesses as leishmaniasis, which affects internal organs – giardiasis, an intestinal disorder – and trichomoniasis, which is a sexually transmitted disease.

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