A silent epidemic of typhoid that is resistant to multiple antibiotics is spreading across Africa, posing a fresh threat to public health, according to a landmark genetic study of the organism.

An international team of researchers analysed the DNA of nearly 2000 typhoid pathogens from countries across Asia and Africa and found that a single multiple- drug resistant strain had swept through Asia and crossed into Africa over the past 30 years.



Nearly half of the organisms studied belonged to the resistant strain, called H58, which has steadily pushed out older strains that are susceptible to common antibiotics people buy over the counter or take to protect themselves from the disease.



Salmonella typhi, the organism that causes typhoid, infects 22 million people globally every year and kills about 200,000. The disease causes fever, headaches, constipation and chills, making it hard to distinguish from a variety of other infectious diseases.

The pathogen is spread through contaminated water or food, and by carriers who pass the bug in their faeces and urine. Though vaccines are available, they are not in widespread use in Africa and Asia. Instead, people rely on antibiotics to treat the infection.

But the broad usage of antibiotics has driven drug resistance in the organism, and as the H58 strain evolved and spread, it acquired resistance to frontline antimicrobials, and newer drugs too, such as ciprofloxacin and azithromycin. In some regions, H58 is displacing strains that have been established for hundreds of years.



“We were all amazed at what we saw. When you see the data, it’s pretty stark. It’s very convincing that it’s becoming the dominant strain,” said Gordon Dougan, a senior researcher at the Sanger Institute near Cambridge. “This is one of the first pictures we’ve had of how antimicrobial resistance is impacting on the way we treat infectitious diseases, and how we will have to tackle them.”

The consortium of 74 researchers from leading laboratories found that H58 emerged in South Asia 25 to 30 years ago and spread to Southeast Asia, Western Asia, East and South Africa and Fiji.

The strain jumped from South Asia to East Africa several times, the scientists report in the journal, Nature Genetics. Tests on 138 bugs collected in Kenya, Tanzania, Malawi and South Africa revealed evidence for an unreported wave of infections across the African states. The strain arrived in Kenya at least 10 years ago, and Malawi about 5 years ago.

“The most striking thing to me is that typhoid was previously considered a disease of Asia, not Africa. This has transformed the global epidemiology,” said Dougan. “This beast can get into a new area and it’s at an advantage, because a lot of competition is wiped out by antibiotics.



Vanessa Wong, a researcher at the Sanger Institute and first author on the study said that global surveillance was critical to address “the ever-increasing public health threat caused by multidrug-resistant typhoid in many developing countries around the world.”



The global spread of the strain requires “urgent international attention,” the scientists write in the report. “This is killing 200,000 people a year and no one is really noticing,” said Nick Feasey, a co-author on the study at Liverpool Tropical School of Tropical Diseases.

The H58 strain is found in Katmandu, and researchers anticipate a wave of infections from the drug-resistant strain in the aftermath of the devastating earthquake that killed more than 8,000 people in Nepal.



Improved surveillance for the drug-resistant bug should help public health officials work out which antibiotics will treat local typhoid infections, and which drugs will be wasted on patients. In some regions, it may make sense to place strict controls on antibiotic prescribing, or withdraw certain antibiotics completely, though the more effective drugs may be too expensive for some countries to afford.

