The rise of antibiotic-resistant typhoid is driven by a single clade or “family” of the bacteria that cause the disease known as H58, new research has shown.
Multi-drug resistant H58 is responsible for a previously unreported wave of infections in eastern and southern Africa that may represent an ongoing epidemic, said the scientists.
Dr Kathryn Holt, one of the researchers from the University of Melbourne, said: “Multi-drug resistant typhoid has been coming and going since the 1970s and is caused by the bacteria picking up novel antimicrobial resistance genes, which are usually lost when we switch to a new drug.
“In H58, these genes are becoming a stable part of the genome, which means multiple antibiotic-resistant typhoid is here to stay.”
The scientists mapped the genetic codes of 1,832 samples of the typhoid bug Salmonella Typhi collected from 63 countries between 1992 and 2013.
The microbe is an especially nasty form of the S. enterica bacteria that commonly cause food poisoning.
It is chiefly spread by swallowing contaminated water.
The lead researcher was Dr Vanessa Wong, from the Wellcome Trust Sanger Institute in Hinxton, Cambridgeshire.
She said: “The data were produced by a consortium of 74 collaborators from the leading laboratories working on typhoid and describes one of the most comprehensive sets of genome data on a single human infectious agent.
“Typhoid affects around 30 million people each year and global surveillance at this scale is critical to address the ever-increasing public health threat caused by multi-drug resistant typhoid in many developing countries around the world.”
Vaccination against typhoid is not widely available in these countries, which rely on antimicrobial drugs to control the disease, said the experts.
The research, reported in the journal Nature Genetics, showed 47 per cent of the samples analysed belonged to the resistant H58 clade.
The strain emerged in South Asia 25 to 30 years ago and spread to south-east Asia, western Asia, east and South Africa, and Fiji, the scientists found.
Professor Gordon Dougan, another member of the Sanger Institute team, said: “H58 is an example of an emerging multiple drug resistant pathogen which is rapidly spreading around the world.
“In this study we have been able to provide a framework for future surveillance of this bacterium, which will enable us to understand how antimicrobial resistance emerges and spreads intercontinentally, with the aim to facilitate prevention and control of typhoid through the use of effective antimicrobials, introduction of vaccines, and water and sanitation programmes.”
The study was coo-authored by Dr Stephen Baker, from the Hospital for Tropical Diseases, an Oxford University clinical research unit in Ho Chi Minh City, Vietnam.
He said: “These results reinforce the message that bacteria do not obey international borders and any efforts to contain the spread of antimicrobial resistance must be globally co-ordinated.”