Study identifies pathogen epidemic in sub-Saharan Africa

A research team has identified the emergence and spread of rapidly evolving non-Typhoidal Salmonella, an invasive intestinal disease, in sub-Saharan Africa.

The spread of the new form of Salmonella Typhimurium bacteria resulted from hubs in South and Central Africa and appears to have been potentiated by the African HIV epidemic. The disease, also known as iNTS, has acquired several genes that provide resistance to several front line treatment drugs.

The blood-borne infection kills approximately one in four people in sub-Saharan Africa. In the rest of the world, iNTS is self-limiting, causes acute inflammatory diarrhea and it is fatal in less than one percent of people infected.

"The immune system susceptibility provided by HIV, malaria and malnutrition at a young age, may provide a population in sub-Saharan Africa that is large enough for this detrimental pathogen to enter, adapt, circulate and thrive," Chinyere Okoro, a joint first author from the Wellcome Trust Sanger Institute, said. "We used whole genome sequencing to define a novel lineage of Salmonella Typhimurium that is causing a previously unrecognized epidemic across the region. Its genetic makeup is evolving into a more typhoid like bacteria, able to efficiently spread around the human body."

The team created a phylogenetic, or family tree, to depict how the pathogen evolved. The researchers determined that the first wave came from a southeastern hub approximately 52 years ago, while a second wave originated approximately 35 years ago, potentially from the Congo Basin.

"The HIV epidemic in sub-Saharan Africa is thought to have begun in a central region and underwent expansion eastwards, a strikingly similar dynamic to that observed for second iNTS wave," Robert Kingsley, a joint first author from the Wellcome Trust Sanger Institute, said. "Our findings suggest the current epidemic of iNTS and its transmission across sub-Saharan Africa may have been potentiated by an increase in the critical population of susceptible, immune-compromised people."

The researchers showed that the next step is to determine how iNTS is transmitted in sub-Saharan Africa so that an effective intervention strategy can be implemented.