Tracing the Evolution of a Deadly Microbe Salmonella bacteria are human and animal pathogens that are found everywhere. When this bacterium infects a person, it causes an illness called salmonellosis, which affects millions of people around the world every year. These illnesses typically cause gastrointestinal problems but if the infection progresses to the bloodstream, it can become a serious disease that needs to be treated with antibiotics, and may result in death. Scientists have now learned more about how one strain of Salmonella bacteria found in Africa evolved to become deadly. The strain, called Salmonella Typhimurium ST313, has killed hundreds of thousands of people in Africa who are immunocompromised. It’s thought to be responsible for the deaths of about 50,000 people in Africa every year.