A news story by Michael Price in Science: “Sleeping sickness hides in human skin”.
[Annette MacLeod] examined the samples for the sleeping sickness parasites and found them in a handful of people, even though they showed no symptoms of the disease at the time. Further testing revealed that mice with parasites in their skin, but undetectable levels of the parasite in their blood, can easily transmit the disease to tsetse flies. Taken together, these results indicate that human skin is likely an “unappreciated reservoir of infection,” MacLeod and colleagues report this week in eLife. People who display no symptoms and have virtually no parasites in their bloodstream can still carry the disease and transmit it to others if they’re bitten by tsetse flies, she says. Skin-to-skin transmission between humans is technically possible, she adds, but is likely rare because it would have to get into broken skin.
The upshot is that if health agencies only test people’s blood for African sleeping sickness—the most common practice—they’re going to miss remnants of the disease that prevent it from being completely eradicated. “These asymptomatic people are the secret reservoirs that keep the disease going,” MacLeod says.
This makes a lot of sense. A reservoir in asymptomatic individuals, with long-term possibility of infecting new hosts, is an essential for human pathogens of the Pleistocene.