Scientists have discovered a deadly new genetically mutated strain of Salmonella is killing 25% of infected people in Africa.
Salmonella enterica Typhimurium is a sometimes nasty foodborne pathogen that causes diarrhea and intestinal problems but the strain is typically non-fatal. Like most foodborne pathogens, Salmonella enterica Typhimurium was thought to only pose a lethal threat to children, the elderly and those with immune systems weakened by disease. Similarly, the strain recently discovered in Africa was believed to kill only people with compromised immune systems.
But now collaboration between African and UK scientists to genetically sequence the strain (called ST313) has shown that it has mutated to become resistant to many commonly used drugs.
The bacterium is thought to have emerged in the last decade and has since infected people in West, East and Central Africa. In 2002 the mutated, drug resistant Salmonella Typhimurium ST313 represented 95% of Salmonella Typhimurium found in Africa.
People unfortunate enough to ingest the foodborne pathogen usually develop a high fever and often seek medical treatment having already contracted septicemia, often referred to as blood poisoning. By the time septicemia sets in, it is often a sad prognosis for the victim. The drug resistant Salmonella kills one in four people, even when the Salmonella is treated with drugs that the bacterium has a known sensitivity to.
The collaboration teams analyzed 50 samples of bacterial DNA from the blood of patients with severe symptoms of salmonellosis, a Salmonella infection, and who were also suffering from an immune compromising illness such as HIV, malaria, malnutrition or anemia. The scientists then compared the genetic sequence of the mutated Salmonella Typhimurium with those of Salmonella strains typically associated with milder illness. What the researchers found was that Salmonella Typhimurium ST313 had mutated and acquired a set of genes that makes it resistant to most antibiotics.
“Salmonella is a bacteria which we know is passed on to humans from eggs, meat or milk, but we think this bacteria could be coming off cutlery and crockery. It’s in the home and everyone, especially small children, is vulnerable,” said Robert Heyderman, director of the Malawi-Liverpool-Wellcome Trust program, one of the research collaboration teams.
South Africa’s National Institute for Communicable Diseases (SANICD) is working to establish an international database of Salmonella DNA fingerprints that will help health officials to protect people. But surveillance for such diseases is poor outside South Africa, so no one knows how many people have been infected or died.
Richard J. Arsenault, 2010
