Contagious pathogens spread and evolve in those with suppressed immune systems.
Nguyen Huy Kham/Reuters
Salmonella, which we typically contract from tainted food and experience as unpleasant but not extraordinarily threatening, poses a much greater risk to people with HIV. Their suppressed immune systems allow a specific strain, Salmonella typhimurium, to infect their blood and cause
invasive, non-typhoidal salmonella (iNTS), a far more serious disease with a death risk of up to 45 percent. In sub-Saharan Africa, a highly invasive form
of iNTS has developed; researchers are attempting to understand how and why the epidemic is spreading.
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METHODOLOGY: Researchers in the UK sequenced the DNA of Salmonella typhimurium from populations with iNTS in Africa, and compared this information to global populations, using "family trees" to trace the bacteria's evolution.
RESULTS: Almost every sample of the bacteria from all over Africa was found to belong to one of two closely related lineages. One form appears to have emerged 52 years ago. The other, which replaced it, is 35 years old. Chronologically and location-wise, both are associated with the HIV's spread across the continent. The second likely emerged after becoming resistant to the drugs used to treat the first.